Isuzu Trooper help

[Subfixer]

I have a 91 Isuzu Trooper, 2.8 TBI, 4X4, 5spd.
Two problems:

It will turn over and start but stalls in about 1 second.
It takes about 10 tries to get the truck to start. I have to keep my foot to the floor or it won't start.

Once it starts, I still have to keep my foot to the floor as it runs real rich (black exhaust) until the revs get up to 3-4K rpm. Then it clears up.

It does this every time I try to start it, warm or cold, even if I turn it off and immediately try to restart.

Problem 2:
Once it starts, it idles at around 2K rpm.

If I block the air feed to the IAC valve, I can get the idle down to around 850 rpm. I replaced the IAC valve, but there was no change. TPS is correctly set to 5.0 vdc (key on, engine off) also.

I've checked all the vacuum lines and sprayed WD40 around the base of the TBI without finding any problems. I checked the brake booster also.... no change.

Intake manifold gaskets were replaced last summer.

This problem started two nights ago after the truck sat for a month. Made the 60 mile trip home, high idle and all.

The check engine light does not come on and there are no codes stored in the ECM.

The high idle still sounds like it could be a vacuum leak, but I have yet to find it. Don't know if the hard starting is related, but I assume it is.

Help!!!.

[Subfixer]

OK, Here's the update....
Rebuilt the TBI and Fuel pressure regulator.... no change.

Replaced both fuel injectors..... no change.

Pulled the intake manifold, replaced the gaskets..... no change.

While the engine was running, I individually disconnected each of the sensors. After each disconnection, the check engine light came on and indicated a bad sensor (low voltage). At least it looks like the computer is keeping track of things.

On a cold start (overnight), the engine idles as it should around 800 rpm. I am able to turn it off and start it up again without any problems. After it's running for about 5-7 minutes, the idle kicks up to 1800-2000 rpm and I can't get it to come down.

No trouble codes are pointing to any problems.

Once warm, it still exhibits the problems noted in my first post.

I used an exhaust gas analyser on it, and after the initial rich startup (once it starts), it is running very lean at that high idle.

Now I'm really lost........ cracked head maybe???

[G Winter]

Have you checked the cat or cats? Does it run warmer,that would be an indicator of plugged cat. Checked the vacuum? I assume you have checked the aircleaner. Have you changed the plugs? If so are you sure they are gapped right? I don't know if this engine uses a dist. if so is the timing correct.Are you sure the gasket between the TB and the intake is correct?
(no vacuum ports covered etc.)
Just a little brain storming with you. Maybe get lucky and hit on something.

Glenn

[bradfordsvettes]

Have you scanned for codes ? I think the next thing to check may be the coolant sensor if the sensor is telling the computer it is 40 degrees below zero you would have issues like this .I have seen more than my share of them out of spec just a thought Steve

[Subfixer]

All the basics have been covered. Engine temps are normal, no overheating of anything like that. Have good exhaust flow. New plugs, correct timing, etc....

No codes are at the ecm except the correct code 12 indicating the ecm is working.

If I disconnect any of the sensors, the ecm sets the appropriate trouble code.

As far as I can tell, the engine appears to have the charactaristics of a massive vacuum leak. When attempting to start after warming up, it takes about 8-10 tries to get it started. I think that gas is just pouring in to compensate for too much air.

Once it starts, and I clear out the excess fuel, it is running extremely lean at a high idle of around 1800-2000 rpm.

Next step I am thinking about is replacing the MAP sensor, as this may be telling the idle air solenoid (IAS) to stay open. If I block the air intake to the IAS, I can get the idle back to normal. The IAS is new and the wiring between it and the ECM is good.

[bradfordsvettes]

the temp sensor for the ecm and the cooanlt gage are seperate units on most cars. it would be worth a scan to double check to see if it is in spec . the computer may not set a code for the coolant sensor as long as it is not totally out of wack Steve

[Subfixer]

Thanks Steve. There are 2 coolant sensors. I've got the correct one feeding the ECM. New temp sensor and MAP sensor on the way. I'll keep you posted.

[samsmith]

i recently purchased a used isuzu trooper and i found this similar problem. i don't know if this is my fault or it was sold to me with this kind of error. i am just a newbie in car and doesn't have any technical ideas about isuzu repair. but when i read the comments, i followed all the suggestions. now i have seen that there was a problem on the coolant.