1999 Rx300 Weird Codes...help!

[kovacs4816]

I have a 99 RX 300 with 145k miles. Last year I had the transmission rebuilt and it has been giving me issues since. One hour after we picked the car up from the shop, it threw a P1153 code. I didn't think much of it, I'm pretty mechanically inclined, so I would check the MAF and/or replace the 02 sensor. Before I had a chance to do this, as my wife was driving to the store, it locked itself out of overdrive and started running rough and threw these codes: P0300 Random Cyl Misfire, P0302 Cyl 2 Misfire, P0304 Cyl 4 Misfire, P0306 Cyl 6 Misfire, P0171 Fuel System Too Lean Bank 1, P1153 A/F Sensor Response Bank 2 Sensor 1, B2798 Communication Fault #2 (Keyfob). I took it back to the shop that worked on the transmission and they told me it looked like the ECM was faulty, I called the Lexus dealership in Fort Wayne, In and they are saying that it's rare to find an ECM faulty. Also, the keyfob has always given me issues, sometimes working and sometimes not, only unlocking the drivers door. It's looking like it will cost me an arm and a leg to take it to the shop, so I need some help! If i reset the ECM it will drive fine for a few hundred miles, first the P1153 codes comes on and then shortly after that the other ones follow and lock me out of overdrive.

[Filehorse]

It could be any number of things but the symptoms you describe are also caused by a failed ignition coil. I've had two coils to fail on my 2000 RX300 and both times the symptoms are exactly the same. Beware the codes you are getting. While they may be pointing to something else, occasionally you'll get codes which are - on the surface - unrelated to the root cause of the problem. Based on the two coil failures I had approximately 1 year apart, I went ahead and preemptively replaced the remaining 4 coils last summer. You really need to get the codes read by your Lexus or Toyota dealer since the generic OBDII codes may not point to the exact source of the problem.

Hope this helps.

[kovacs4816]

I do have an appointment next week at the Lexus dealership. In the mean time, I am trying to troubleshoot this as much as I can to save some money. After speaking with the very helpful people at Fort Wayne Lexus(which were on the phone with me for 30 min. helping me), they pointed out that there are seperate coils for each cylinder, and for all 3 to go bad would be surprising. He told me to clean my oil control valve and see if that helps. He did mention the MAF sensor being faulty or the timing being off. I cleaned the MAF and it looks pretty good, and as for the timing, it runs perfect until the CEL comes on, no hesitation or anything. So I'm assuming that it's not the timing. I may be wrong, but I'm shooting in the dark here.

[Filehorse]

I think this may be something that your Lexus dealer can probably troubleshoot pretty quickly with their proprietary diagnostic equipment. Otherwise, you're faced with throwing time and parts at the problem hoping something works. If this were my problem, I'd plan on the dealer service department handling this - as much as that's gonna hurt. A Toyota dealer can perform the same service so you might want to check what their hourly rates are since this will be a flat-rate hourly charge. Usually, if you let them fix the problem, they will comp the cost of the diagnostic analyzer which typically is a $75-100 charge.

Let us know what the problem eventually turns out to be. Inquiring minds want to know.

[kovacs4816]

It's not going into the shop until late next week. With a week to spare, I am determined to fix this. Any info or suggestions are greatly appreciated. I will post my findings or post the dealerships findings, whichever come first!

[lenore]

I would definetly clean the oil control valve on the camshaft...they are located on the battery end of the engine. one bolt and they come out and can be cleaned....Now the bad news....You may have engine sludge which is causing the Variable valve timing on the camshaft to fail.....This would cause missfires if the camshaft time were way off. I would pull the front valve cover which is easy and take a look....Sludge would look like big gobs of jello or worse.

[kovacs4816]

I will pull the valve cover off tonight and check it while I'm cleaning the OCV. I have always been meticulous about oil changes and maintenance, so I'm hoping that's not the case. The weird part is that it's not throwing a code for the OCV and it runs fine until all the misc codes come on. It constantly has code P0171, so I'm going to measure voltage and resistance on my O2 sensor as well. I did change the starter right before this mess started, and I had to remove some hoses to get to it, so I will investigate that as well. I will post my findings tonight!

[kovacs4816]

UPDATE: Pulled plugs, coil packs, valve cover...etc...everything looked ok other than one of the plugs being gapped 2x specifications. Put it back together and started throwing same codes....I'm stumped. Goes to the shop Friday.

[kovacs4816]

Ok, here's the deal. I kept going back to the oil control valve being the issue. I checked resistance, voltage, working order...etc. and it seems ok. When I unplug it though, all of the codes go away. Even the 02 sensor code. 400 miles with no misfires or codes, other than the one I am getting from the valve being unplugged. So I am going to order a new valve and see what happens.