Sporadic Misfires - Any Insight?

[blk_on_blk]

Replaced all the spark plugs with NGK Iridium factory-spec plugs last night, rotated the coil packs, and it seemed to run smooth as silk last night before closing up for the night. Although, this morning on the way to work there was the sputtering and CEL again. Two codes this time, right back to the P0300 and P0303. The symptoms of sputtering and much, much less now, and seem to be getting less as times goes by, but it's not resolved.

So, I've replaced the OCV, so it's not that. I've cleaned the MAF, and it's not that. I've replaced and rotated the coil packs, so it's not that, and I just put in fresh properly gapped plugs, so it's not that. I guess I'm down to it's the fuel injector on the #3 cylinder.

Any other insight or suggestions?

[blk_on_blk]

An update on this weird issue I'm having -

I brought the vehicle to my trusted mechanic/shop. Driving it in that morning it drove smooth as silk until about mile 18, then it started to sputter a little and throw a code/CEL. I checked the code when I got to the shop, and it was the repeated P0300 and P0303. I had written an overview of the symptoms, what had been done on the vehicle (replaced spark plugs, replaced #3 coil pack, cleaned MAF, replaced OCV, etc.) to give the tech a head start.

They had the vehicle about two days and finally called and said it was ready to pick up. The owner wanted to talk with me, but I missed his call, so he left a voice mail. He sounded a bit frustrated and said they couldn't pinpoint the problem. They took it out for a drive and after about 20 minutes they got the CEL again (I had cleared the code before I dropped off the keys with them). Again, the P0300 and P0303. The owner said the P0300 is so generic there isn't much info that can be taken from that, so they looked more to the P0303. They first went right for the coil pack and exchanged it with the #2 pack. From there, they drove it randomly throughout the day for about an hour total and couldn't get any codes or any sputtering... so they handed it back to me.

I picked it up the next day and it drove nicely nearly to work, but then started to give the little studders with a flashing CEL as I got close to work. I checked the code when I stopped, and it was a lone P0303 code. The owner of my shop said he knew there was something going on, but it wasn't revealing itself enough for them to find it. He suggested in may be a fuel injector issue.

Anyhow, I drove the vehicle home in the evening, and it drove very well... a little bit of studdering at about half way home, but then went away and drove smooth. The strange thing is that the problem seems to be getting progressively less and less. I tried filling up with plus grade fuel to see if it had any effect. We drove it down to the Salem area this afternoon and it ran beautifully for about 50 miles, but then had some notable studdering in the last 10 miles. I checked the code when we arrived, and it was again the P0300 and P0303.

The info I did get from the shop wasn't too enlightening. Here's the report from the analysis:

STFT: both banks normal

LTFT: bank 1% lean, bank 2 6% rich (the owner said this isn't ideal, but not way off either)

MAF readings low: 4.2 gps @ idle

cylinder balance, 50 rpm deviation

I had cleaned the MAF, but the readings are still a bit low... yet the STFT (short term fuel trim) readings are normal... but the LTFT (long term fuel trim) readings are off, although a 5% deviation is considered normal. I'm wondering how much impact can a wacko MAF have on performance.

I've been following the performance issues and as the issue falls into a sporadic random pattern, the sensation of the fault is as if a 'choke' is being kicked in sporadically and really quickly while I'm driving, but then it suddenly drives smooth again. It's never really an on/off effect, but rather like little tiny quick repeated spurts of a choke coming on... what I'm getting at is that it feels like it's being "controlled"... like it's a sensor going wacky and freakin' out for a bit, then going back to controlling properly, not like an issue of a dirty injector or clogged fuel filter or other physical component failure. Who knows, maybe I'm the wacky one at this point... but with that sensation, I've ordered a new MAF.

Now that the shop can't find it, I don't feel so dumb, but I'm also at the point of starting to just replace parts and see what fixes it. I think it's a gremlin, which often stems from electronics. I'm thinking the MAF... maybe something sporadically shorting out somewhere, maybe the ECM. But then again I don't know exactly all the symptoms a faulty fuel injector would cause. Why would the code repeatly be on the #3 cylinder? I've changed the coil pack, changed the spark plug... the only thing left is the fuel injector. The old plug I pulled out looked good... not fouled, not scored... just looked like a nicely worn plug.

(heavy sigh) So, I'll report in later next week after I change my MAF and let everyone know what the result is. Hopefully when I find the culprit it may help someone else diagnose a problem like this. The $100 at the shop to run a diagnostic didn't tell much, but at least it's more than I knew before.

Do any of the readings on rich/lean and/or the MAF trigger any red flags for anyone regarding diagnosis?

As always, thanks again for the input/help!

One last thing, I came across this website: http://www.aa1car.com/library/2003/ic30336.htm and here's the symptoms they give for dirty injectors:

"The fuel feedback control system will compensate for the leaning effect once it is in closed loop, but it can't correct the underlying condition that is causing the problem. The injectors need to be cleaned, if an engine is experiencing any of the classic symptoms of dirty injectors, such as lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power, and higher hydrocarbon (HC) and carbon monoxide (CO) emissions. Lean misfire may also trigger a misfire code and turn on the Check Engine light on 1996 and newer vehicles with OBD II systems. The code often will be a P0300 random misfire code, or you may find one or more misfire codes for individual cylinders, depending on which injectors are most affected."

Sounds like the problems I'm having... if the MAF doesn't do the trick, new injectors are going in.

[jimP]

Stop, dont buy those injectors yet! I just got my2005 RX back from a 2.5 weekstay at local Lexus dealer. It was flashing cel & vsc.I dont Know what codes it sent but dealer said it was consistantly showing "cyl 5 missfire" They replaced the injector,coil,sparkplug,removed valve cover to check for broken spring,did compression check.No luck,contacted japan. I recieved call to pick up car it was BAD GAS. I suspect vandalism because I also filled containers for my boat and they are good Think back as to your activities and maybe your problem has a simple solution. Good luck.

[2005lexusrx330]

I have a 1999 Rx300. @ about 100,000 mine started doing the same thing. It was the coils. I would replace the spark plugs and coils from all of the 3 back spark plugs. They are hard to get to.

The front ones are easy to replace, and can be done as needed.

That fixed my problem.

I've got a '99 RX300 with ~134K on the odo and it has recently started to have random sporadic misfires. It first showed up on an hour long trip back from the Salem area last week. The CEL light would flash, then the engine would smooth out and the CEL would turn off, then do it again. When I got home I pulled the codes. It was P0300 (random misfire) and P0303 (misfire in cylinder #3)... I went straight to a faulty coil pack because of the miles and the known failure of the coil packs. I changed out the #3 coil pack and pulled the battery cable to let the ECU reset. Once done, I took it out for a test drive and it ran smooth... for a while.

The next day the engine ran smooth half way in on the drive to work (about 11 miles), but then it started to misfire again... again, I got a flashing CEL... then the CEL stayed on. I thought I might have gotten some bad gas, so I filled up at a trusted station, threw in some injector cleaner, and it drove smoothly... for a while. Later in the day the CEL started flashing again. When I pulled the code, I again got the P0300, P0303, but also the P171 (bank 1 lean). So, I've done some searching and it seems it could be one of a few things (assuming the new coil pack isn't also faulty):

Faulty fuel injector

MAF

Oil Control Valve (but this seems to trigger a whole side of misfire codes, not just one)

Bad Spark Plug

I went to the easiest first (seeing that the #3 spark-plug is a buggar to get to) and got some spray automotive electrical cleaner and cleaned the MAF. It was dirty, but cleaned up nicely. I put it back in and started the engine... it started smoothly, and as I took it out for a drive, I could feel a faint misfire sporadically... it would run smooth, then the faint misfire, then run smooth. It wasn't enough to trigger the CEL, but it probably will if I drive it more.

Here's what I'm thinking on some of this. I don't think it's the Oil Control Valve, since it would show up as a full side of the engine with misfires (to my understanding). It could be a bad MAF, and cleaning it just reduced the problem. It could be a faulty fuel injector, but how to test for that? It could be a bad sparkplug, but why would cleaning the MAF help reduce the misfire if it was a spark plug... if it truly has reduced it.

So, at this point I'm not sure what I should go after next... any suggestions? I guess it's to where I should just start replacing things, since it's not even enough to trigger the CEL, but it's still misfiring.

Here's an overview on misfires that I pulled off the web: "A random misfire code can be set on newer vehicles with OBD II onboard diagnostics when multiple misfires occur randomly in multiple cylinders. The cause is typically a vacuum leak in the intake manifold, throttle body or vacuum plumbing, a defective Exhaust Gas Recirculation (EGR) valve that is leaking exhasut into the intake manifold, or even bad gasoline. Less common causes include bad spark plug wires, worn or fouled spark plugs, a weak ignition coil, dirty fuel injectors, low fuel pressure, or weak valve springs. If a misfire is occuring in only one or two cylinders, you will usually find a misfire code for that specific cylinder rather than a random misfire code."

Any input/suggestions are welcome... thanks in advance.

[blk_on_blk]

Thanks for the input guys. I have replaced all 6 spark plugs and a couple of the coil packs, then rotated the coil packs to see if the trouble code follows. It doesn't.

At first I thought this problem might be bad gas, too, but I've been watching it and it's so sporadic... enough so that I keep driving the vehcile to try and toubleshoot it. I've gone througha about 5 tanks of gas now, and one I ran all the way down to nearly empty. I then ran a full tank of premium (coworkers said fuel manufactures are starting to run higher percentages of ethanol in the low grades of fuel, so it should run cleaner with premium). I also ran one tank with fuel injector cleaner in it. All resulted in the same freakin' thing happening.

We got back last night from the Salem area and the CEL was flashing at me nearly the whole trip home. When we got home, I popped out the MAF and cleaned it again. Upon starting it up again, it ran better... hmm. Then, this morning on the drive in I started to get the flashing CEL again, but right towards the last part of the commute the light went off and the vehicle drove smoothly. There was one point while sitting at a light that I could feel slight little surges and stumbles of the engine... very slight, but they were noticable... but not enough to trip the CEL. Then, while sitting in Drive at a light, as if someone flipped a switch, the engine went whisper smooth, RPMS dropped a little, and it drove great for the last few miles.

When I pulled the codes as I got to work, I had a handfull of them: P0300, P0302, P0305, P0171, P0100, P0110. The last codes refer to the MAF, and this is the first time I've ever got a code for the MAF.

What I know now is that what ever is causing the problem is sporadic, and when it acts up, it sometimes trips the CEL and sometimes not. That tells me what ever is the culprit is 'working' within the limits for the most part, but just not working correctly... then it drifts out of the limits, trips the CEL, but then drifts back into the limits and CEL shuts off... but all the time it's still crappin' out. It seems like what ever is failing is triggering other related codes, but not the primary code for the component that's failing. Since I've changed coil packs and all the plugs, and I've replaced the OCV, it now down to either the MAF or the injectors.... my money is on the MAF, but I'm still not sure why it has been giving a consistent P0300 and P0303. Perhaps the P0303 (#3 cylinder misfire) is the most affected by a spasmatic MAF.

I read somewhere that if you are having symptoms like these, a way to check and see if it's the MAF is to have the engine running and idling and to disconnect the MAF and see if it runs a little better. If so, then it's probably the MAF. Now, I have no idea how influencing the MAF is on the system and whether or not it directly controls the primary functions of combustion or if it's more of a 'trim' and refinement sensor. Well, after getting home yesterday I had the engine idling and it was a touch rough, so I pulled the plug from the MAF and the whole engine totally died instantly. I'd say the MAF has quite a bit more effect on engine performance than just a trim or refinement feature... seems it's a pretty primary component to get it to run at all. If that's the case, then a freaky MAF could be the culprit. I've got a new one on the way and will let everyone know as soon as it gets installed.

Thanks again for helping try and trouble shoot this problem.

[smooth1]

Well, heck, I sure don't feel bad now for not being able to help, you took it in, and they had it in front of them and coudn't fix it! LOL!!

It is starting to sound more and more like a sensor issue. Have you checked the 02 sensors and made sure they were working and resistance was good?

When the engine is first started when it is cold, the engine will briefly run for 1 or 2 minutes in open loop operation based on the "basic" idle mixture setting in the CIS Fuel Distributor/Air Flow Meter assembly and by the duty cycle programmed into the ECU, which may explain why when you first staart the car everything seems good again.

Normally the basic idle mixture is set to be 0.6% to 1.2% Carbon Monoxide (CO) when the exhaust gas is measured up stream of the catalytic converter. Once the Oxygen (O2) Sensor warms up (Heated O2 sensor), the system will switch over to closed loop operation.

This sensor is used to monitor oxygen levels in the exhaust and acts as a voltage supply that transitions high to low when the oxygen level is high (slightly lean above 14:7 to 1 air fuel ratio) and transitions low to high when the Oxygen level is low (slightly rich air fuel mixture below 14:7 to 1 air fuel ratio).

The ECU uses this oxygen sensor signal to tweak the air fuel mixture back and forth close to the ideal 14.7 to 1 Air Fuel Ratio. With the fuel system in closed loop operation after the O2 sensor warms up, the O2 sensor voltage cycles up and down between ~0.1V and ~0.9V.

At idle, the O2 voltage should cycle back and forth 1 to 2 times per second and when cruising, it should cycle back and forth ~4 to 5 times per second. This cycling occurs because the engine computer senses the O2 voltage and then changes the duty cycle going to the CIS Frequency valve (Mixture solenoid).

If the O2 sensor wire is disconnected with the engine running, the ECU normally has a 0.450 V (+/- 0.050V) reference voltage on the ECU wire connecting to the O2 sensor.

The ECU will switch over to a basic idle mixture setting (frequency valve duty cycle set to 50%) with the O2 sensor disconnected. You can temporarily disconnect the sensor and drive the car to see if the problem still exists. Or if you have the ability to test the sensors, then just do that.

[blk_on_blk]

So, ya’ll want to know what the culprit was? Here it is (see picture)… somehow, and I have no idea how this could have happened, the electrical snap-fit housing on my #3 injector was broken. I’m guessing it’s been like that for years, but just recently either it started to vibrate loose, or just the movement/exposure was causing a poor connection. Either way, I couldn’t see this failure for the injector is buried under the intake plenum. I had initially thought it might be the MAF, but I replaced it the other day and it had the same symptoms… no change. I knew the injectors could stand being replaced, so I pulled the trigger and replaced them all. I went through Motor Man and got all newly reconditioned injectors for $230 delivered over-night (I was torn between Motor Man http://www.fuelinjector.citymaker.com/nipp..._injectors.html and Injector Whse http://www.injectorwhse.com/servlet/StoreFront …Injector Whse had free shipping on all orders over $99, but I had read many good review for Motor Man, and they would ship them out over night for just $18, so I went with them).

I spent Saturday replacing the injectors, and the front rail is cake… so easy. But the back rail makes up for that. I couldn’t get anything under that plenum, so off came the plenum. To do that meant removing nearly my entire intake system. I had to pull the intake air hoses, the butterfly assembly, and then I could access the plenum. What I struggled with is that there are three support mounts behind the plenum and butterfly assembly that one can’t see (see other picture), and they are a serious buggar to get to (two go to metal support posts, and one is a tie in on the pressurized A/C refrigerant line. It’s a job that makes replacing spark plugs or coil packs look easy.

Anyhow, I’m back on the road, no codes, and running fairly well. It’s been a little ‘hiccupy’ for the first few instances of WOT with the new injectors, but after a nice hour long road trip, the computer seems to be readjusting to the new flow of the injectors. The drive in to work today was nice and smooth and uneventful… that was definitely the root of the problem. I don’t know how the injector got broken, or stayed connected that long… in fact, I don’t even know if the connection was the problem (even though the housing was broken) or if the injector was just going bad. Either way, this seems to have done the trick.

I took a lot of pictures of the repair job, so I think I’ll write a DIY for replacing injectors for the RX300. I’ll see if I can get some down-time and write up a tutorial (since I couldn’t find a single thing online of how to replace injectors on our vehicles… I couldn’t even find a picture of the engine with the plenum removed (or any other component for that matter).

Thanks again for everyone’s input and brainpower on this issue… seems to be a weird failure that just wasn’t diagnosable from the symptoms… one had to get their hands dirty to find the root of it.

[smooth1]

Wow, I'm glad you got it fixed! In my first post, (#3), I thought for sure it was the fuel injector, and in my next post I asked you if you had inspected the injector seal. So I was on the correct issue to begin with. But this isn't about being right or wrong, it was a good lesson. Thanks.

[blk_on_blk]

Yep, Smooth, you were right on the money. I didn't initially inspect the fuel injectors because the number three injector (where the fault was) was waaaaaay back under the plenum, and if I was going to do the work to get back to that injector to inspect it, I was going to just replace them all (since with 135K on the ticker it was time for new injectors). The codes and symptoms were not directly isolating an injector, so I was trying to eliminate any possiblity of it being something else before replacing the injectors. I was dreading the job, and for good reason, but now that it's done, it wasn't too horrible... just takes a lot of patience and manipulation of tools in tight areas that one can't see. All new (well, reconditioned) injectors installed for about $225 isn't too bad.

Thanks again for all your help on diagnosing this issue (and to all others who gave their input, too). Your insight really helped me narrow it down to the injectors.

[tmastres]

Glad you solved it man, that was a tough one!

[lsangmook]

Yep, Smooth, you were right on the money. I didn't initially inspect the fuel injectors because the number three injector (where the fault was) was waaaaaay back under the plenum, and if I was going to do the work to get back to that injector to inspect it, I was going to just replace them all (since with 135K on the ticker it was time for new injectors). The codes and symptoms were not directly isolating an injector, so I was trying to eliminate any possiblity of it being something else before replacing the injectors. I was dreading the job, and for good reason, but now that it's done, it wasn't too horrible... just takes a lot of patience and manipulation of tools in tight areas that one can't see. All new (well, reconditioned) injectors installed for about $225 isn't too bad.

Thanks again for all your help on diagnosing this issue (and to all others who gave their input, too). Your insight really helped me narrow it down to the injectors.

Thanks for your extensive posting. I'm sure it's been pain for you. I have 2000 RX 300 with 140k and it started having very similar issues. My trusted mechanic replaced O2 sensor but CEL came right back. After getting some maintenace jobs; new belts, battery, etc., CEL still appeared after 5 to 20 miles of driving. One thing I noticed is that when I drove locally (low speed), CEL came on around 5 miles of driving. When I drove high ways, CEL didn't come on until I slowed down to local driving.

I tried this after resetting CEL, because after reading yours and others' postings, I suspected an issue with fuel injector.

I wanted to try fuel injector cleaner before I try to get a new set of fuel injectors. One review site recommended 'Lucasoil' and 'Techron' brand. I bought Lucasoil at Autozone for $10 and started using it. What a surprise, on the first day, CEL disappeared. It came back on second day and I added more cleaner and on third day, that dreadful CEL disappeared again. It's been only few days and I've driven 50+ miles with highways/local mix. So far so good.

When CEL came on first, it gave me a whole set of code, 0300, 0303, 0171 and others. I believe there were like 6 of them at that time. In any case, I think I was in luck to get CEL out with fuel injector cleaner but for those who don't have much skills in mechanic division like me, it wouldn't hurt to try fuel injector cleaner first to see if that takes care of the problem.

I'm getting ready to tackle that intake valve cleaning thingy for low idling issue but I hope I can help few to save time/money/agony to go thru this CEL problem.

Thanks,

[truhaart]

I realize this thread might be too old for a reply but here goes...I've been driving my 99 rx300 for one month. I purchased it in Houston and drove back to central Texas with no problems, smooth as silk. It is a clean car with only 91K. Yesterday, I had to accelerate hard and quick to avoid an accident. About five miles later, I stopped at a store and when I started the car to leave, the cel began flashing and I got the sputtering and missing thing. O'Reilly printed out codes P0300, P0303, and P0304. I also noted that the trac control off light comes on after startup. Is this going to be the same problem I see in this thread? Which replacement should I start with? Any suggestions would be greatly appreciated.