RX&ES300

Just to update, I finally got my RX to run great (knock on wood - Knock! Knock!). Initially, which started this whole project, I had a P0303 error and ended up replacing the #3 cylinder coil with a new one from Autozone (and later verified that indeed the original one was faulty). After replacing it and 6 new spark plugs, things went from bad to worse as I ended up with P0300, P0303, & P0304 codes. I went back and totally cleaned out the throttle body and the IACV (already did the MAF/IAT sensors before) and took the opportunity to recheck that all the plugs were gapped properly (which they were) and that the coils were firing. While all coils were firing properly, because of the P0303 & P0304 codes, I decided to swap the new coil which was on the #3 cylinder with the one on #2, and swapped #4 with #6 thinking that if there were more errors and by chance were P0302 or P0306, I had isolated my problem to the coils. The car started and while it idled much much better, it was still rough and misfired during acceleration. Within minutes, I got a CEL and went to Autozone to read it...sure enough it was P0302, the newly replaced coil. I pulled the coil out in their parking lot, and upon close inspection, saw a some small amount of carbon deposit (from arcing) and traced it to a hair line fracture in the tube. Luckly enough, Autozone had another one in their stock, and replaced it free of charge, and LO and BEHOLD, this time it was the original Denso part number and not the replacement one. Dropped it in, screwed it down and now have driven 30+ miles without even a studder. Hopefully, this has solved my problem. Two notes: 1) Prior to going back to Autozone to read the codes, I checked out the fuel injectors and they all were "clicking" with the exception of #3 which I couldn't get to. Given this, I have decided not to run the BG44K as who knows what internal damage it may do to the fuel system while cleaning it. Everything seems to be good so I'm leaving it "status quo". 2) I'm still not sure if my IAT sensor is OK or malfunctioning, depending on which pins should be used for the resistance testing. But I tend to lean towards the "OK" given that I'm not seeing the CEL and the car is running smooth. But I will change out the MAF if I get some fuel/air related error codes, just to be on the safe side. Thanks all for your insight and help.

Sounds similar to what I was having with the exception that I did not get a P1133, but I did want to check out if the MAF was working correctly. Actually, there are two sensors housed together - the MAF sensor and the IAT (intake air temp) sensor. To the test the IAT sensor, you are looking for a specific ohm (resistance) readings across two pins on the MAF at given temperatures while for the MAF sensor, you are looking for a fluctuation of voltage across two other pins. As you may see from the above threads, the issue has been around the accuracy of the Lexus factory service manual when it comes to which pins to use for the IAT test which artbuc pointed out. Actually, I hope he's right which would mean that my MAF is good but for the sake of your testing, I'll share the pins that I used and the ones the FSM specifies. For purposes of these tests, let's first identify the pins by position in the MAF housing. Looking at the MAF's connector in it's normal orientation ("plunger" down), I'll refer to the left most pin as #1 with the right most pin being #5. You will need a VOM meter and compressed air (in a can will do). I had done my testing after I had cleaned the MAF and IAT sensors. IAT Sensor Resistance Test Using a VOM meter - place it into OHM mode: the FSM's instructions for the RX300 place the positive (red) leads on the 4th pin and the negative lead (black) on the 5th pin. For the ES300, the FSM places the positive lead on pin 2 and the negative on pin 1. (Once again, the reason why I give you both configurations is because I found that when using the RX pins, my readings were out of this world and artbuc pointed out that I should be using the ES pins...but you may want to test both for yourself). Note the resistance reading at your room temp. For my testing, I went a bit further by placing the MAF into my freezer for 15 min, did another reading, and then placed it outside in the sun and did another reading when it heated up (it's been in the mid 90's in Denver lately). This gave me enough of a swing to see if the values are changing/tracking which would most likley indicate a properly functioning IAT sensor. If you want to take the guessing out, measure the temps in the freezer and the outside and keep the meter attached as it warms up. The resistance readings should fall within the following ranges...you may need to do some interpolating based on your temps (for instance, at 72 deg, you'll be closer to 2000 ohms than at 68 deg): Ambient Temp in F..........Ohms ....-4.......................13,600 - 18,400 ....68.........................2210 - 2690 ...140..........................493 - 667 If your readings don't fall close at the temp ranges, chances are that your IAT sensor is malfunctioning. MAF Sensor Test Attach the MAF sensor connector back on to the MAF but keep it out of the air filter housing. Using the VOM, place it into DC voltage mode: for the RX300 - use pin 1 for the negative (black) lead and pin 3 for the positive (red). For the ES - use pin 3 for the negative and pin 4 for the positive. I gently slid my probe in between the rubber around the wire and the actual connector housing until it made contact (bottomed out). Make sure that you don't push too hard as you don't want to damage the connector. Turn ignition ON (but don't start the car). You should see a voltage reading. Now apply compressed air into the MAF chamber and you should see the voltage fluctuate. If it doesn't, replace the MAF sensor. Let me know what your findings are if you chose to do the tests.

artbuc - thanks for the insight...it's not very comforting to hear that the FSM can have such fundamental errors for their own product. Any suggestions on which 3rd party manual to get?

I may have found the problem and it may be with the Intake Air Temp (IAT) sensor housed on the MAF. To test it, the manual says that you can read the resistance but to use different terminals/pins depending whether its for a RX300 or ES300. The reason why I ask is because the readings using the ES terminals (left most two when looking directly at the connector) are correctly measuring 2100 ohms at 72deg F while the RX terminals (right most two) are reading over 17 million ohms. FYI - the readings in both the ES and RX configurations changed when I changed the temperatures (I placed it the freezer and then outside it the sun, and the resistance changed as the MAF warmed up and cooled down) and the ES terminal tracked correctly while the RX terminals continued to be way off. What I would like to confirm is whether the manual is correct that the RX300 uses the right most two terminals/pins for the sensor?

Smooth1 - appreciate all your help and suggestions. I'm off to check things out and will keep you updated on how things go.

So you're cool with using rebuilt ones? But I think I'll run a tank with BG44K through first before I go down the route of changing injectors. I think I figured out little black canister - it's the vacuum surge tank feeding off the VSV assembly.

Boy - I really missed the boat on where the filter is. So what the heck is that small black (filter-looking) canister that feeds the fuel into the injection rack? Also, where can I get the 6 Denso injectors for $150? Every where I looked, $150 is the price for 1.

Thanks for the feedback. I checked the gap on the even cylindered plugs and all three were slightly greater than .040" which leads me to believe that the other bad boys will be too. So buying them from Lexus may have saved me the effort of having to go pull and regap the 1-3-5's. I'm heading out to the parts store to pick up the filter but for the sake of not sounding too dumb, I'm assuming that it's the little black canister hanging just prior to the fuel injector manifold on the driver's side, more or less between the oil filler cap and the throttle body? And to change all 6 injectors, it appears that I'll need to remove the air intake manifold unless there's another way. This looks somewhat ugly. Thanks

Smooth 1 - thanks for your reply. Good questions and to answer especially 1 & 2, I went out and tested it: 1. The CEL came on after 4 mins, once the engine warmed up (it hasn't been run today) and RPM dropped from ~1300 to ~ 1000. 2. I reset the CEL and drove the car keeping the RPM's under 2k. The CEL came on within 1 min. FYI - When I was driving aroung yesterday, it seemed to be running smoother/less misfires at higher RPM's (3k & over when the O/D did not engage) than at lower ones but then again, it may it's just less noticeable at higher RPMs. 3. I didn't touch the gap -- the dealer told me that they were all preset and each plug was secured in a collar. But in retrospect, I should have double checked to ensure that each was correctly gapped. DUH! 4. I triple checked them before "closing shop" on the project on Friday but haven't check them since. I'll have to pull the cover off and wait until the engine cools off before attempting to snake my hand in under the intake manifold 5. Nope - the coolant has been at steady state for well over a year and the car has never overheated (we're the original owners). However, when my wife initially mentioned it was running rough, I did the typical checks and found the oil to be two quarts down (well, two quarts brought it to mid-point between the two "bumps" on the dipstick so maybe it was a little more). I hope that being low didn't suck more "crud" of the bottom of the oil pan than usual especially since it's overdue for an oil change by 1k miles. 6. Fuel Pressure & Pump - nope, haven't look at that. Any suggestions on how best to do that and the recommended PSI range? The guy at Autozone mentioned checking the fuel injectors but also recommended to first run BG44K on a full tank of gas to clean out the intake and injectors. That was one the next things I was planning on doing before changing out a bunch more sensors or coils. But I'm game to try anything else that you may suggest. Thanks for your insight and help.

I seem to be having similar problems to blk-on-blk's. My '99 RX300 AWD with 110k miles started idling rough and misfiring last week resulting in the CEL light to come on. I dug through the various posting (many thanks goes to LOC for such a super forum) and cleaned out the MAF, psuedo cleaned out the IACV (meaning that I only took off the black IACV magnet cover on the throttle body and found that it moved freely enough so I only sprayed the cleaner into to it vs take off and clean the whole TB) and cleared the CEL by removing the EFI fuse. While this made the car idle and run better, the idle still was rough and misfiring and the CEL came on but this time only blinking. So off to Autozone where they read a P0303 code - UGH!!! I bought the coil from them which actually was an OE (Denso) part at almost half the cost ($59) of all other parts shops which were selling 3rd party coils. Since I figured I was already going to be tearing apart the back side of the engine, I hopped over to Lexus and bought a set of Denso Iridium plugs from them (got a deal for $11 each). Installing the replacement coil became somewhat of a challenge. I found that the original part (90919-02234) was superceded with a 90080-19016 (which is what I bought from A/Z) according to some of the postings. However, it appears that it is not a 100% replacement as the "rings" on the tube of the coil are more "pronounced" than the original allowing it to only slide part way in (up to the 1st ring). From postings, it appears others have also run into this same problem and explained that supposedly Toyota made "minor" engine changes mid model year but that most parts stores don't know anything about. From everything I read on the web, it sounded like electronically the parts were interchangeable but that the "rings" prevented them from fitting. So I lightly sanded down the rings with extra fine sand paper and made it fit perfectly. The car ran great for 10 or so miles on a couple of short trips around town: no CEL's, no misfires, no rough idle, great acceleration. Then it started again...same rough idle, etc. Went to Autozone and read the codes...this time: P0300, P0302 and P0303. On the way back home, the transmission wouldn't kick-in to O/D even though it changed properly on the way to A/Z. Turned the engine on and off which didn't help any. So I reset the CEL (pulled out EFI fuse) and low and behold, the O/D worked again!!! I got home and verified that all the vacuum hose, connections, etc were all connected and seated properly (which they were). So I'm back to dealing with the P0300, P0302 & P0303 codes -- ANY ONE HAVE ANY SUGGESTIONS? (Sorry for the long posting but thought that something that I did might be important and trigger a solution). Thanks in advance for your help.