arfghan

Looong story, but want to give you as much detail/progression as possible ...
1995 GS300, 167,000 miles.
First if all, the CEL light had been on for 2+ years. I thought I had to go to Lexus to check it and the car was running great, so we ignored that. Last June or so, we had driven about 45 minutes then parked for around 45. It started up and ran normally. Drove 1/2 mile to the freeway, then after about a 1/2 mile ON the freeway, it died. It did not want to start but finally did, roughly. Drove few miles then exited and parked. Came back in a half hour and it would not start. It would turn over, but would not catch. Smelled gassy. Had it towed home .Btw, checked and there was no gas spill on the flatbed after he unloaded the Lex. It still would not start when we reached home. That was the start of all this.
..As we went on, the car would start normally, seemed to run normally for about 6 to 9 minutes, then would slowly tach down and die. Rev-ing when it tached down would not keep it running. After it died, it would not start again until the next day. (Would turn over but not catch.)
..After I figured out how to read the codes, I replaced both O2 sensors as directed. No change.
..Evidently this model/year does not have the MAF that you clean with the spray can cleaner. Whatever that part is called, I cleaned it properly with compressed air. No change.
..Mobile Mechanic decided the car did not know when it was warmed up and continued to dump gas into the engine instead of choking down. Replaced the engine coolant sensor. Wow! it started and ran 25 minutes no problem. Drove it out the next day. 5 miles to town. Had the oil & filter changed. (lotsa gas in there so mechanic said get it done right away.) Was driving over to get a car wash and fill up when it died again. Would not start same as before. Towed home. Again. This time it would not start even the next day. Same mechanic was out to tune our remaining daily driver and looked again at the Lex. He said it was dumping gas into the engine. Was able to start it by disconnecting the fuel pump.<That mechanic was to come back to work on it, and elected not to return.> Now car doesn't start at all.
..Next Mobile Mechanic hooked fuel pump back up, did a complete tune up and replaced the valve cover gasket.. And, it would not start. <That mechanic also was to come back to work on it, and elected not to return.>
No change..Car does not start.
..Third Mobile Mechanic came out to do a diagnostic. Said the timing was good, the spark was perfect, but it had way too much fuel.
++At this point, in addition to those 3, I had also conferred with 3 other mechanics who had no useful ideas.++
..I then removed, had rebuilt, and yesterday replaced the ECU. OK. Now, the car is back to starting, but again dies after a few minutes. Then won't start until later/the next day.. Starts now, dies.
Addendum. After all this, post ecu, now when it starts, it runs very roughly. Had white smoke exhaust today but I'm sure one of the mechanics said head gasket ok and no water where it didn't belong. Did not run rough before when it did run for those few minutes each time.
Today, when I started it, the tach was different. Very low, around 1000. Running rough, as I said. After a minute the tach started bouncing from 1000 to 1250, another minute or so it worked up to 1250 to 1500 bounces, then 1250 to 1750 bounces then rev-ed up to a 2000 bounce and back down. Almost like I was hitting the gas, but I was touching nothing, just watching it. Tached down and died after 7 minutes. Wouldn't start again.
So pretty much same-o, same-o with variations.
Now, a note. Some of you have seen my previous posts about this and know, I am NOT a mechanic. I'm a grandma who loves this Lexus and doesn't think it should be dead. So, yah, I'm stubborn. The most I have done myself before this was add fluids when needed! So, please, when you give me ideas, be very specific and speak for a non-mechanic. I'm fairly capable, I just don't know this stuff innately like many of you do. I am a determined Mechanic-in-Training.

twojayzee

Anyone done a compression and leak down test on the engine for you ?

Jostar

I has a similar issue with a 93 SC300, It was the fuel ecu, I did bypass is/12V mod, But your issue might be your engine ECU, Try another one over the one you just rebuilt.

What I am seeing in the post, your new rebuilt ecu starts the car but the fuel pump ECU might be overheating & kills the car hence the RPMs just dropping little by little, that is due the lost of fuel pressure when the fuel ecu shuts down..