Off Idle Hesitation

[WBB]

1992 Typhoon

Recently bought truck has been sitting 2 yrs. and would crank but not start. Replaced plugs, rotor, cap, leads, and fuel filter. Will only start with shot of brake cleaner, after warm will start on own. Afterwards it will idle although fluctuating 800-1200 rpm. It has a severe off idle stumble and is not drivable, but by feathering gas it will rev high and smooth, above 2000 rpm (with no load) it does not have this hesitation problem ??? Scanner shows no codes but timing advance is 24 deg. at idle??? When throttle is opened quickly off idle engine stumbles, advance dips breifly (fraction of a second) to 10 deg. and then up to about 34 deg. full advance and engine revs high. Throttle body and plenum cleaned. Vacuum lines inspected and replaced. Compression 150-160 psi all cyl. Removed exhaust to test but same. Any ideas ???

Update:

When engine is cold and started it will rev easily from idle but as soon as it starts to warm this hesitation problem returns. Faulty ECM, EST ???

 

[bezerk]

Re: Off Idle Hesitation

have you checked you O2 sensor, and try to disconnect the O2 sensor, see if it helpes it will throw a code but will go in open loop

 

[WBB]

Re: Off Idle Hesitation

Thanks........ Waiting for fuel pressure tester to test that. Does the Typhoon use a special hi-volume fuel pump? Any recommendations GM or aftermarket? If I pull O2 sensor when warm will ECM still lean mixture because of ECT input or would this temp. sensor be by-passed? Is 24 deg. advance timing at idle normal for this engine ???

 

[bezerk]

Re: Off Idle Hesitation

you can unplug your O2 sensor and it will go into a safe mode for running, you don't have to worry about it going rich or lean, just try it. buy a walbro feulpump if you want to replace it

 

[WBB]

Re: Off Idle Hesitation

Update:

No difference with O² sensor disconnected, still waiting to check fuel pressure.........

 

[gkrcr882]

Re: Off Idle Hesitation

Verify that you are getting the correct fuel pressure and volume first, then go from there. You will also need to remove all the old gas from the system so that there is one less variable.

 

[Rexxenexx]

Re: Off Idle Hesitation

Did you solve this WBB? I have a similar problem. Mine starts up first shot with the coolant temp sensor disconnected. If connected it has a hard time starting.