I have an 02 GS300 with about 148k on it. The car isn't raced, it drives me around town and is very well maintained. About six months ago it started running really rough. Autozone said it had multiple misfires so I took it to my shop and they said it needed a tune up. Changed, plugs, wires, coil packs. Put good stuff back in. Reset codes and disconnected and reconnected battery. Ran like a CHAMP.

Fast forward to about 3 weeks ago. Car started running rough, same scenario. VSC lights, check engine light, idle all jacked up. Took it to get codes checked and it was multiple misfire again. Took it to the shop and they did a compression test (passed), swapped plugs around, wires around, coil packs around. It SEEMED to follow the coil swap. Changed the coil (new) AGAIN... still runs terribly. Checked the injectors, swapped them around... no change. It went from cylinder 3 (before coil moved) landed on cylinder 1 (added NEW coil pack). Now it says multiple when previously it was narrowed down to one. After new coil replaced it began to run fine and then when put in gear and under load started up again.

I have done everything I have read in all of the other posts (MAF clean, compression test, swap injectors, replace parts, disconnect battery, tighten battery connectors, etc etc) and I'm STILL at square one with a horribly running GS. I LOVE my car but I'm at my wits end! Does anyone have ANY ideas?

My car does have 20's on it and it also has a sound system (professionally installed). I don't know if that has anything to do with it, but I thought I would add it, especially since it seems electrical. I hate writing new posts when there is already SO much information on here, but I can't find anything else that comes after what I have already done. I really don't know what to do and don't want to get ripped off at the dealer for them to run tests and come up empty handed too. Has anyone seen anything like this before, a misfire problem so in depth?

Please help, even if it is off the wall ideas that you have heard in the past. I REALLY appreciate any and all guidance. Thank you, thank you in advance!!!

Alex

 

hmm. how are the grounds?

seems kind of odd since it ran fine for a while and now its acting up again.

 

idle air control valve? maybe.... any other codes?

 

The only codes are the multiple misfire codes. Someone else mentioned the OCV but other guys said they changed theirs and it wasn't fixed. I'm at a loss right now!!

 

Could be a throttle body issue. Throttle control motor maybe? Is it going into limp mode?

 

I would still change the OCV. I had the same problem you're describing.

Only about $100 bucks on ebay(OEM Part)
(I got mine from the dealership since friend works there)

Resolved my issue, but I had also changed out the plugs and wires too.

 

Don't know if you ever got this issue resolved but I had a similar problem when I performed maintenance on my 2000 GS300. The problem was the plug wires. I used some non-OEM wires that I got off eBay, trying to save a few bucks. The connection was not good on plug 3 and I kept getting the 0300 and 0303 misfire codes. I am changing to OEM wires TODAY!