Bernett1

I have seen many threads on this topic. I just wanted to share something with the Lexus/Toyota community. I recently purchased a 2000 Lexus RX300 with 158,000 miles on it. I like working on cars so I checked my spark plugs and realized they were the original iridium plugs. I decided to change my plugs and remove the intake manifold. That was a tough job only because of that darm 14mm bolt on the back of the plenum. Shortly after replacing the plugs I noticed my transmission was shifting roughly between 1st and 2nd gear and 2nd and 3rd gear. I searched the forums and it seemed to be a common problem. I thought it was funny that this happened after I removed the intake manifold. I then got a check engine light and it was the bank 2 oil control valve codes. I read all the forums and was about to remove and clean the valve but one of the forums mentioned a bad ground. I thought about my recent intake manifold replacement and realized that I probably didn't tighten the 10mm bolt that hold grounds on the back of the plenum. I checked that bolt and found it was loose. I tightened it this morning and have been driving my RX300 without any of the previous symptoms. I thought this was worth mentioning because I consider myself a good mechanic and things like this add to my experience. So for those of you experiencing problems that are difficult to explain I suggest checking all the ground connections on you car. Today's electrical components don't seem to handle small variations in voltage. You see many solutions to problems by just putting in a new battery. Well if your grounds aren't good you won't get proper voltage to your sensors and they may start throwing codes. I'll check back and let our community know if this really worked or if it is only working for a short while. I hope this helps because my next steps would have been to clean the oil control valve then drop the transmission pan and change the fluid and the filter and maybe next begin changing shift solenoids. I hope this helps someone avoid a costly repair.

ukrkoz

Well, there is no need to remove plenum to do spark plugs on this car to start with. I did it twice in about 45 minutes. Remove throttle body and on the passenger side, there are some brackets that have to be unmounted to clear passage. been few years, not exactly remembering. But then, you have plenty of room on either side to slide hands through those opening, and reach ignition packs and plugs. Scraped forearms for sure but... One on the pass side is easy, as you can see it. Worst one is one in the middle, that's "by touch" job, but not really that hard. And I have BIG hands.

Bernett1

I agree that you can change those back plugs without removing the plenum but my plugs hadn't been changed in 158,000 miles. I was glad I did remove the plenum because they took a fair amount of force to get them out. I put them back with anti seize bu I don't expect to have to change them again since I put back iridium plugs. Removing the plenum wasn't difficult except for that one bolt. Now that it has been loosened I don't think it would take me long to remove it again. I'm glad you and others can remove your plugs without removing the plenum. I just wanted others to be aware of how sensitive our sensors may be to variations in voltage and getting good grounds is really important.

lexina

Bernett, Thank you for sharing your issue. I am sure it would help someone in the future when things just break and you have no clue where to start.