gmgod

I am experiencing this with the 92. I have replaced the plugs, wires, cap and rotor. The car only does this at 500 to 1200 rpms with just a hair of throttle. If your moving up in traffic from a stand still (slowly) and let back off the throttle completley it will try to die and then surge back a little. The car is a LB9 auto. I am going back out to check the timing and if that does'nt solve it I guess I will break down and buy a volt/ohm meter for the TPS and jack with the IAC. Oh, the car runs great otherwise - does'nt miss, pulls strong, etc.

gmgod

The timing was 2 degrees retarded, set it back to 6 degrees BTC. Runs better but still has the dead spot.

ERICCAMARO

doesnt sound like a tps problem. Possibly a dirty Iac could cause this. When is the last time you took your throttle body off and gave it a good cleaning?? If you havent it is definantly time. I had a similar problem before on an 87 Iroc that I traced back to a bad EGR valve. I would check the egr valve and the egr solinoid. plug up the vaccum line that comes off the bottom of the throttle body and see if that helps any.

gmgod

Thanks for the reply, do you still think it could be the iac if the car idles good and smooth? The hesitation is only there after you get in the gas ever so slightly just off idle. I just bought the car, so I hav'nt done much yet but I will take the throttle body off and check.

ERICCAMARO

Sounds like a fuel problem to me. If it doesnt happen at idle then its not the IAC, I doubt it is an ignition problem if it doesnt happen through the rpm range but when is the last time you changed your fuel filter?(these should be changed every 10k) these can cause problems like this, but you have to make sure that the problem is only right off idle and is not happening at higher rpms. it will be alot harder to notice when its revving higher. IN your first post you said that the problem is happening at 500 rpm? your car should idle at around 750 I would clean your throttle body and set your minimum Idle air. if you dont know how theres a tech article about it on this site. sounds like its about time, may want to set your tps too but I dont think there adjustable in 92 I have a 92 and mine isnt but I drilled the wholes out bigger so I could adjust it down to .54 volts. good luck

gmgod

Ahh, good call on the non-adjustable iac. I've never owned one this new. It is definatley only happening just off idle and only when you get in the gas very lightly. If you give it a little or a lot more throttle it will not hesitate and at wot it runs suprisingly well all the way to 5000 rpms. Do you think it could still be the fuel filter if it runs that well at wot? Also, it does idle at around 750 when warm and in park. In gear it idles at aroud 500-600 rpm.

ERICCAMARO

doubt its the fuel filter if its only effecting it through a few hundred rpms. first of all how many miles are on the engine and what ALL has been replaced. When is the last time you replaced the O2 sensor? if you havent within the last 20k Id throw one on there, If it doesnt fix the problem it sure wont mess it up any, sounds like you may be running a little rich right off, possibly the ecm thinks everything is allright but if you have a old O2 sensor theres just no way of it telling whats goin on. You may also want to try disconnecting the negitive terminal of the battery for about 30 min. to reset the ecm, should be done after every tuneup or modification. good luck have you made any progress yet?

gmgod

Well, no progress yet but I have now observed that it only happens in open loop mode. I'd say the o2 sensor is a good idea since the plug wires, cap and rotor looked to be originals. With it only happening in open loop I am leaning toward a sensor, but there are no codes stored so I don't really know. I'll replace the o2 and if that does not cure it I'll try a new map sensor. As far as what all has been replaced, just the plugs, wires, cap and rotor so far. I just bought the car a little less than a week ago. It has 145,000 miles on it

gmgod

Replaced o2 sensor, still no dice. I'm gonna swap the map for a known good one today.

ERICCAMARO

145k on original engine :hail: . Might just be time for a new timing chain. I have 130k on mine and its starting to go, my problem is very similar to yours too, exept for mine stumbles a little at idle too. see if that map helps. how do you know it only happens in open loop??

Steve89GTA

Dude.
Don't swap any more parts.
Disconnect the vac line that goes under the plenum to the EGR and try again. It bet that's the problem.

ERICCAMARO

Just so you know i already suggested that :lala: :lala: .

but it does make sense and if it is the problem its free to fix and you dont have to spend anymore money. but if you want to fix it right and not just plug up the line you will have to replace the egr solinoid probably. I think I have a bad solenoid but I havent done anything about it yet. there like 50 bucks. what a rip.

gmgod

So if I disconnect the line that goes to the plenum from the egr solenoid will that make the egr stay closed? What if its so carboned up it won't close all the way? I'm gonna try it and see what happens. I know it only happens in open loop because if I fire it up stone cold and drive it during the first few minutes before the computers minimum temp for open loop mode is reached it won't do it.

gmgod

Well I'll be a mother-jammer, I disconnected the line and it quit. Many thanks Eric and steve, Now is it the valve or the solenoid? This is the 3rd 3rd gen I have owned and will be the third egr valve/solenoid I have replaced.

ERICCAMARO

probably just the solinoid needs to be replaced, Hopefully anyways, good luck

V8Steve

I've had a similar problem for too long to admit (3 yrs). My throttle body shaft is worn in the housing so much I can feel the lateral play. It's worn in the range used the most and that's just off the throttle stop. I think a momentary vacuum leak happens just at that point. Last year I installed a new BBK 52 mm and the stumble went away. There were other problems with the BBK so I returned it. Of course, my stumble came back when I put the old '85 IROC TB back on the ZZ4.

I still need to find a way to rebush the body so this annoying problem will go away.

Steve Anderson