I have a very annoying hesitation that occurs when I start from idle. If I get on it hard it is fine - no hesitation, but if I drive it under part throttle (normal driving) it goes-pauses-goes.

It happens hot and cold. Injectors are all rebuilt. Wires, cap, rotors, and plugs replaced not long ago. Plugs may be fouled since replacement (that's why the injectors were rebuilt) - would that cause this problem? Any other suggestions? No codes, and I have doen the IAC/TPS adjustment several times with no changes to this problem.

Thanks for your help

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87 GTA 350 TPI, 700R4,
K & N, Accel cap/rotor/wires, SLP airfoil, ported plenum

 

check to see if your o2 sensor is clogged.

 

You are correct in thinking that the spark plugs could be fouled.
DId you perform a balance test on the injectors after the rebuild?
The MAP sensor is another potential problem area that may need to be addressed. Check for a code 33 or 34. You may e-mail me for more detailed info on the MAP.
Also check your timing and be sure that the EGR is not stuck open or operating at or just above idle.
An alternator putting out less than 9 volts will also cause drivability probs.


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"84Z28/'91 305TPI comp cam flowmaster TB coolant bypass/shutoff valve to heater core MAT relocated Ram-Air(home-made) gutted air-box IROC ground effects/wheels GY245/50's 700R4 superior shift kit/ corvette servo(excellent shift kit BTW) Rebuilt engine and transplanted it myself. Love this engine!
LOW performance people should drive low performance vehicles!

 

sounds like egr ... you can check it by lifting up on the diagram from the bottom and see if it comes back down. also, check the vacuum line and see if there are any leaks by sucking on it and see if the vacuum maintains. i had that problem a while ago and the egr valve fixed it.

[This message has been edited by Allan (edited September 11, 2000).]

 

could be a bad TPS aswell, look for a smooth sweep of the tps voltage from idle up to WOT (when you open it by hand of course)
btw JP 87's had MAF systems not MaP thats 90-92

 

Quick questions...

Did you ever clean the IAC passages and the IAC pintle?
Did you remove your MAF screens?

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.587 @ 107.97mph (1.710 60ftr) on the long runner setup.
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels. Stock Wheels. No Weight Reduction.
Gunning for NA 11's with the MiniRam II and Hooker LT Headers.
-=ICON Motorsports=-

 

Thanks for all the responses. Here is some feedback to some of them:

NO codes
Injectors cleaned and flow balanced
EGR - could be a potential problem I suppose
No detectable vacuum leaks (spray tested )
O2 - don't know if it has ever been replaced; I was going to replace it when I put headers on.
MAF screens are removed
IAC/TB all cleaned up
TPS check shows smooth voltage increase & decrease
Alternator works AOK
Timing is bang on

At this point, based on these responses, I am suspecting the plugs and likely the O2. I don't want to deal with the EGR since it is a major pain to get at under the plenum.

 

well, then, going by that I would go ahead and check the egr and definitely replace that o2 sensor. I forget how often they recommend changing it, but it's like $20 so it's not a bad idea to change it. I think they recommend every 30K miles? seems a bit low, but again, i'm not sure.

 

The condition you mention resembles a mis fire. Due to the fact that it happens under load leads me to believe that the sparkplug wires need to be checked out. Open the hood in a dark garage and look for arching plug wires and listen for the "click" of an errant spark.
You mentioned that you replaced the sparkplug wires, there are some cheap brands out there that will easily allow the spark to jump to ground, so be sure this is not happening. Also, the wires that you have to assemble(crimp the connector on after cutting to length) are very difficult to achieve a satisfactory connection so I would suspect these too.

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"84Z28/'91 305TPI comp cam flowmaster TB coolant bypass/shutoff valve to heater core MAT relocated Ram-Air(home-made) gutted air-box IROC ground effects/wheels GY245/50's 700R4 superior shift kit/ corvette servo(excellent shift kit BTW) Rebuilt engine and transplanted it myself. Love this engine!
LOW performance people should drive low performance vehicles!