Have a car at our shop that is giving us grief...

Idle surge has been present throughout all of this, the timing issues / popping out intake/exhaust is more recent. Pops just like an old distrubutor car if you advance timing too much.

Scanner shows the car is running 30* of timing at idle and over 45* just off idle. Have replaced just about everything electronic on the car - no changes - even PCM. Set base time on it several times but continues to do this each time.

Replaced MAF, IAC, EGR, Module in Dist, Cap, Rotor, Tested TPS, Fuel Pressure, Coil - all good.

Any guesses would be geat at this point.

Thanks - Mike

 

check the map vacuum line, TPS voltage, and the coolant temp sensor. the older GM computers will flip **** if any one of these 3 things reads wrong or irradically. coolant temp is the most common cause of issues like this, TPS is second.

hope this helps.

 

TPS voltage is usually the culprit if I see a buddy of mine he had this problem with his iroc also I believe raising the tps voltage was part of the sollution I will ask him if he did anything else

 

Thanks guys, but TPS tested good with scanner and reads well even with a DVOM. I'm not the one doing the service on the vehicle, but we've all been looking at it over the week here - even some GM employees have come to take a look. I am leaning to something more mechanical, pickup on the distributor? Is there a CPK on a TPI motor? Sheesh... I am almost embarrased to ask that

On occasion the car will jump from closed to open loop several times in the matter of 30 seconds or so???

 

if it is jumping open and closed I would say 02 or maf then even if they are functioning they may be screwing up

 

Changed both... lol. Changed the MAF twice even

 

90% of our work is restoration, so this kind of stuff is frustrating for us. LS1 and even LT1 cars are much easier to diagnose. I cringe when I see a TPI or a Crossfire car roll in

 

if you seea c rossfire roll in just roll it right back out and tell them to stop taking hard corners. lol

as for this TPI problem. is the car throwing a check engine light at all? and have you checked all the different sensors and the vacuum lines under the intake?

throw a post up on Thirdgen.org ill bet someoen has seen thsi before and can tell you whats wrong.

 

No Light... I had an idle surge problem on my T-Rammed Z, but it was MAP related, the timing thing is what really takes the cake. I forgot about 3rd gen.org - Thanks

 

ok talked to my buddy he said it was his 02 sensor and tps voltage he said he raised the voltage to alittle above 50 and it was alittle better but not perfect then he changed his 02 and it was all set. he does have a cam though.

 

really simple shot in dark is u sure-sure the plug wires are correct. I stared at a TBI truck that ran shitty like u describe and it was a perfectly incorrect wire. just trying to help.

 

30* is a lot of timing at idle. I'm running 22* at idle and 34* at WOT for now. I will increase the WOt timing more. TPS-.50-.55 for autos.

Is the surge just at idle in gear or in park or both?