Ok so i have set my iac to roughly 400 rpm(rpm gauge doesnt work so im kind of guessing) tps is set to .54 volts. When the car is in drive the idle surges and the whole care rocks forward sounds like it wants to stall then surges and stays running. Driving around its fine and i have no engine codes. I just put in a new tps sensor, i have done plugs and wires, 8 new fuel injectors, and a fuel filter. I do have a bad exhaust leak at the y pipe but i dont think it has anything to do with it surging in drive. In park the idle is much more smooth i can hear an occasional skip but that could befrom the exhaust. . At wits end with this thing and im trying not to go to a chevy dealership for idont have much faith in them finding whats wrong and i could be spending thousands and never fix the problem.

 

Bump anyone there?

 

Mine did this and the IAC was loose so I had a vacuum leak. Also could be standard service items- plugs/ wires/ cap or some of the injectors. Process of elimination I'm afraid

 

Ok update, i took out the iac and cleaned it, it looked pretty new put everything back together and the care still surges at idle in drive. I took off one of the fuel line and it seemed to bleed air for a long time. I think there maybe to much air in the fuel lines which is what cause the car to surge? At this point i feel its a fuel issue i have played with the tps and iac already. I did change the fuel injectors and fuel filter before. When you give the car gas its fine until you stop at a light and the whole car rocks back and forth surgeing. Help please im new to the third gen

 

clean your air filters

 

Will do maybe it will help, the car runs fine in park it doesnt surge unless its in drive

 

Not sure what year u have but Dirty/bad maf ?

 

Its an 89 305 tpi this is what has been done to the car. I bought the car with a bad fuel injector it would not start unless the injector was unplugged. Put new bosh injectors, plugs and wires, fuel filter, new tps, cleaned the iac and set it and the tps to .54 the car had a very high idle while driving which i have gotten down with the new tps and the iac set. The main issue when the car is started it revs very high for a little while then as it warmsnup the idle drops down. When driving ther e is no power loss or surging. At stop lights the whole car rocks and sounds like its going to stall but doesnt. In park the car idles fine with no surging. Agian i unhooked the fule line yesterday and all i could hear was air pissing out for a while not sure if thats how it should be.
I also cleaned the maf and the car has no engine lights right now
Also the car has a bad exhaust leak either at the y pipe or closer to the maifolds trying to figure out this idle issue before i put a custom exhaust on it, dint know if its related bjt im trying to give as much info as i can

 

I think you may want to try a new IAC. When you apply the brake with an auto trans the computer limits the amount of air (through the IAC) to reduce the idle speed. When you take your foot off the brake pedal the idle should jump back up. It does this very subtle and unless you really pay attention you never notice this. It sounds like this may be your issue as you say it only happens when in drive with your foot on the brake. Sounds like The IAC is searching when you are depressing the brake pedal.

 

Okay i will try a new iac and change the air filter ill update with the results im open to anyone with ideas so keep them coming thanks agian

 

Ok update put a new iac in the car seems to have stopped surging for the most part. I do have a slight skip or a miss at idle but nothing under load also i have a code 36 now any help guys i will say the exhausg leak is at the passenger mainfold and you can smell exhaust really bad and tbeare car is ticking like crazy any suggestions? Should i put hookers on it or just replace the manifold gasket