ES250OG

I have a 1991 es250 5 speed with a 2.5 L V6. When I'm in neutral or with the clutch engaged I can rev the engine Full Throttle half throttle doesn't matter and it's fine. However when I'm in gear and I start to release the clutch anything over about 1,500 to 2000 RPMs the power just cuts out sometimes the car will stall, but it starts right back up. This doesn't happen all the time, and temperature seems to have no effect it happens cold or warm. I know these issues can be a nightmare everyone replacing injectors mass air flow sensors Etc. I think I'm going to start with replacing the ECU but I wanted to see if anyone out there might have a better idea?

LeX2K

How many miles? Maintenance history?

ES250OG

just about to roll into 117,xxx miles and I'm the second owner the previous owner didnt say much about the maintenance but having met the guy and judging from how well taken care of the car is, i assume it was well maintained. It was a sunday car for the family and garage kept.

LeX2K

That's a tough one. I have two cars with the 2VZ-FE engine (one is a 5-speed) I've never had anything like that happen. The only real problem I had was the intake snorkel was cracked so sometimes I would hear a whistling noise on a cold start and it would sometimes cause hesitation. Some things of note:

Your car does not have a MAF it uses a electromechanical airflow meter. They don't normally go bad. Do NOT remove the screws on the connector, it is held on by a metal clip.
A bad TPS can cause inconsistent engine performance but I've never seen one cause stalling.
A bad EFI temp sensor will cause poor engine running but it usually triggers the CEL.
Poor connection to the battery can cause stalling and similar symptoms to what you describe.
Maybe a bad fuel filter?

If you can find a replacement ECU for a good price that's a good way to rule out the ECU. Assuming your car does not have California emissions there are two ECU part numbers, the first changes up to the 2nd so they should be compatible.

89661-32560 11/1989 - 09/1990)
89661-32561(10/1990 - 06/1991)

ES250OG

Ok thanks for that. The reason i suspected possibly the ecu is because even before it started doing this was, is, running a rich fuel mixture.

LeX2K

Not a bad idea to replace the O2 sensor (Denso 2344051) at the same time. By the time a bad O2 throws a code the sensor is way way past working properly.

ES250OG

come to think the car does have an exhaust leak either at the manifold or downpipe I'm not sure but it's definitely pre-cat. Could this cause these issues?

LeX2K

An engine will never run properly with a leaky exhaust especially if the leak is near the o2 sensor. Not sure it could cause the engine to stall though.

ES250OG

Im going to park it and over the next few weeks give it a full tune up + some and we'll see what happens. I'll update regularly after each replacement see if i can pinpoint the issue.

ES250OG

So i replaced the fuel filter threw some seafoam in the tank along with some new gas. Runs strong now.

LeX2K

Good to hear.