LexuBarge

Hello! I have a 1993 LS400 with ~130k miles on it.

I was driving locally when suddenly the engine went up and held 2,000 RPM. It had an unusually high idle at a red light, and when I accelerated/turned into the intersection, the engine surged and stalled. I cranked it repeatedly, and it wouldn’t start until about the fourth time. When it did start, it surged before idling high. I tried to drive it, but it drove at 3,000 RPM with low speed before it died again. This happened a couple more times before I just pulled to the side and waited 15 mins. After that, it started up and drove fine. Before this happened, the engine RPMs would surge randomly (1-2 sec.) once in a while, but nothing else. I haven’t been able to record it as it failed, but I did catch the no-start after the stall: .

As far as workup goes, the Toyota dealer (my independent mechanic was off) pulled Code 47 (sub-throttle) and Code 71 (EGR system). They found the sub-throttle position sensor failed electrical testing and replaced it. They also found the EGR valve failed resistance testing, but I declined replacement due to price. I also had the dirty throttle body cleaned and air filter replaced. The alternator and starter were okay. I then took it to my regular mechanic (it drove fine) who said the EGR valve resistance was only a bit out of range. He did find a cracked EGR valve. He was able to reproduce the Code 71 only intermittently, but the Code 47/TPS came on right away. He told me to go back to the dealer to have my TPS adjusted, but the dealer did more troubleshooting and said the Code 47 was coming from a short in my traction ECU.

I decided to take my chances without further repairs. It drove fine for a few hundred miles except for one incident of jerking at highway speed. Then the same high idle followed low-speed stalls came back, and it’s starting to happen frequently. Could it be a bad MAF sensor, IAC valve, fuel pump, ECU, or finicky TPS adjustment? I doubt it’s an EGR problem unless it’s sticking open or the pipe leak is bad. My symptoms are fairly similar to this: https://www.clublexus.com/forums/ls-...-car-dies.html, so it could be the MAF sensor.

I haven’t had major problems with this car in the past. It leaks PS fluid and I replaced the hose, but the leak came back so I refill it with ATF occasionally. Hopefully I don’t have a haywire power steering pump causing electrical problems. I also get the rear bulb failure indication on the dash intermittently (I’m aware of the trunk harness fraying in this model and will look into it). Your suggestions are appreciated!

dicer

I suspect the idle air control motor.