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1991 trooper start/idle problem


Subfixer
12-17-2006, 10:33 AM
I have a 91 Isuzu Trooper, 2.8 TBI, 4X4, 5spd.
Two problems:

Problem 1:

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 the exhaust 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, so I don't believe the fuel pump or filter are the problem areas.

The check engine light does not come on and there are no trouble codes. All I get is the initial code "12".

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.

Subfixer
12-31-2006, 02:07 PM
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???

atfdmike
01-02-2007, 10:07 AM
Hi, sounds like you have covered the basics. I found little about this in the manual, but if you have not looked at this valve, maybe you should? It is the auxiliary air valve. Good luck.





1991 Isuzu Truck Trooper II V6-2827cc 2.8L

Vehicle Level (http://library.alldatapro.com/alldata/LIB~C23949~R0~OD~N/0/34870051/56622313/56623608/56623610/34853741) http://library.alldatapro.com/images/a_003366.gif Powertrain Management (http://library.alldatapro.com/alldata/LIB~C23949~R0~OD~N/0/34870051/56622313/56623608/56623610/34853741/34857029) http://library.alldatapro.com/images/a_003366.gif Computers and Control Systems (http://library.alldatapro.com/alldata/LIB~C23949~R0~OD~N/0/34870051/56622313/56623608/56623610/34853741/34857029/34857030) http://library.alldatapro.com/images/a_003366.gif Auxiliary Air Valve (Idle Speed) (http://library.alldatapro.com/alldata/LIB~C23949~R0~OD~N/0/34870051/56622313/56623608/56623610/34853741/34857029/34857030/34857074) http://library.alldatapro.com/images/arrow1.gif Locations (http://library.alldatapro.com/alldata/LIB~C23949~R0~OD~N/0/34870051/56622313/56623608/56623610/34853741/34857029/34857030/34857074/34857086) http://library.alldatapro.com/images/arrow2.gifhttp://library.alldatapro.com/images/blnk_spc.gifLocationsLower RH Side Of Engine, Ahead Of Starter Assembly

Subfixer
01-04-2007, 04:37 AM
atfdmike, Thanks for the lookup. I'll check it out this weekend. I didn't know it was there.

Subfixer
01-07-2007, 11:47 AM
Well, I looked all over the place for that aux air valve, but I could not find it. Actually, the starter on my 91 2.8 V6 is on the left (drivers side) of the engine. There wasn't any air source on the pass side either.

trooperbc
01-07-2007, 02:08 PM
Well, I looked all over the place for that aux air valve, but I could not find it. ....
do you know that it looks like this...
http://www.paragon-products.com/photos/PP-0.280.140.100-2.jpg
...like this more or less

see the two hose connection points? not small vacuum type hose.
one hose should go to the throttle valve (?i think). one hose should go to the common chamber.

hth

//bc

Subfixer
01-08-2007, 06:25 PM
Hmmmm,,, nope, nothing like that on my 91. Maybe that's only used for automatic transmission setups. I've got nothing that large on either side of the engine. The only large hose I have that pulls vacuum is the power brake booster hose.

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