Hello every body. Say i got a 92 Z28 TPI 5.7 and i got a problem with the idle and on start up . When i crank the car up it rev a little high and comes down even when the car is warmed up and sometimes it idle a little high now i have replaced IAC and TPS as well looked for any vacuum leaks and can't find any so far. So i was wondering if anyone else has had this problem and am i over looking anything.

 

How did you test for vacuum leaks? Carb cleaner trick? Propane? Smoke test? The only one that I've found to be very effective on a TPI is a smoke test. Highly recommend getting or making a simple one to test with. That, coupled with capping off lines etc while it's running and seeing if the problem goes away, is the most effective on a manifold that can hide leaks underneath itself.

 

Well i used the carb cleaner i don't have a smoke tester i wish i did. I have been wondering if it could be the brake booster going bad and could be causing a vacuum leak.

 

You can block off the booster and see if the problem goes away. I don't suggest driving anywhere with it that way though
Making or buying a simple smoke tester with a small paint can is pretty cheap. Google them and you should find a few different ones. The only 'expensive' part is if you don't have or have access to an air compressor. The professional units are very expensive though.
The carb cleaner test is nearly useless on a tpi.

 

Thanks for the info. I'm going to try that on the booster this weekend and i do have a small compressor so i'll check in to a home made smoker. Thanks again for the help.

 

We’re you able to solve this? Having similar with mine @79Daytona

 

Hey calidude. Well I'm not 100% sure it's fixed but after not finding a vacuum leak and the brake booster seem ok but not 100% sure on that so i plan on replacing it sometime down the road. This car had setup for sometime in it past history and i think it was a stolen car one time in it's history as well. So i when back and replaced the IAC and the TPS even thow there only about a year to a year and half old i was thinking the way the after market part that you order online are now a day maybe one was acting funny. Now the TPS i had on the car was for a earlier Z28 which was adjustable so which made it easy to set it at the .054 which i understand is where it should be but my car being a 92 Z28 had the non adjustable TPS . So when i put the new one on i had to adjust the base idel screw down to get it to .054 but even then it was still idling a little high so i turn down the base idle screw a little more which seem to help so I'm guessing TPS set around .050 to .053 so the car is doing ok right now . I'm still not sure what the problem is and what i did I'm sure was not the right thing to do but like i said the car is doing ok for now so I'll keep plugging away at it until one day i figure it out.

 

The tps voltage is fine to not be .54v on the 90-92 tpi. The computer just works with whatever voltage is there for a baseline on startup.
So your throttle was part way open from the idle screw? Is it completely closed now and what's your idle currently at?
If you have a way to scan it then you could see what the computer is commanding for the iac steps.

 

Hey aliceempire. No the base idle screw is not completely close i just turned it down just a little maybe one full turn. As for idle well when it's warmed up and in drive it seems to idle between 600 to close to maybe 700 the tac is a little funny some times if you tap it it will drop a little bit. Now when it's in park it seem to idle around 800 sometime a little bit higher. Man i wish i could get a scanner or knew someone who had one it would make thing alot easier . I know there's still a issue because in the pass the car can be running ok and then out of the blue the engine will surge and idle high and if i kill the engine and crank it back up it seem to be back to it's old self.

 

https://www.aldldroid.com/
is an option. I have not used it myself, I run ebl on my efi car.

 

Cool !! Thanks for the info I'll check it out.