I've got a problem with a stock 91z. It starts and runs good cold, seems to run good when up to temp, but when driving on the road at a steady cruise it has a noticable surge. It's more annoying than anything. It still idles good at normal temp but seems to have a floating idle also. I have checked all the vacuum lines and all seems good, no leaks. The tb and manifold have no leaks either. I have run Seafoam fuel injector cleaner thru it as well as running Seafoam thru the maniflod. It has new plug and the ignition system is in good condition. I'd sure appreciate any ideas as to where to look next.

 

Check you TPS for smooth changes in voltage, or in resistance when disconnected. The range most used would tend to wear out faster causing abrupt changes in voltage when maintaining the TPS in that range i.e..throttle position.

 

does it surge on level road with the Cruise Control on?

 

I will check the tps and see if there is a problem. I am also going to check the O2 sensor as well.

Yes, it is most apparent when cruising on level ground. At the moment my cruise control dosn't work.

Thanks for the replys.

Steve

 

hello, fellow vol!! i live just west on I-40 in crossville, tn. well, i'm having the exact same problem. starts and idles great. i have a 91 z28 350tpi with 138k and get a surge when crusing 40-55 mph. steady pressure on throttle. at first, i thought it maybe a/c kicking on and off, but turned it off, and it still does it. i plan on checking tps for open, o2 for running lean, and fuel pressure for being low/high. please keep me updated on any progress you have. i tried to post a pic, but it said file too big. anybody know how to reduce a pic to post? thanks, and best of luck, tom

 

well, after checking the car out, the tps tested good, no opens. o2 was also good, lean/rich during cruise/surge. fuel pressure was appx 41 psi, a little low. i think the spec's are 41-47. i unplugged the egr solenoid, and couldn't get the car to surge, but the ses light came on for a code 32...lol. anyway plugged the solenoid back in, and unplugged the egr valve. hope that may help someother folks. best of luck, tom

 

Tom, thanks for the update. I also checked the the tps and it was ok. I'll check the egr valve tomorrow and see what happens.

Steve

 

no problem. i just blocked off the vacuum line from the solenoid to the egr valve. i'll keep you updated as i'll drive it appx 60 to work tomorrow (30 each way).