Hey Guys,

I'm hoping someone here can help me out. I have a 1991 z28 5.7tpi that I just bought a couple weeks ago. Ran fine when I bought it. Had to pedal it once to get it to start, but that was it.

Took it to O'Reilly's to have the codes ran. I went to leave and it just started running like total crap. Got it home barely.

NOW, it won't start unless I give it gas and won't stay running unless I keep giving it gas. Once I take my foot off the pedal, it basically idles for 2 secs and then dies. I'm totally stumped. I've never had a car run great one minute, then go to crap 2 minutes later.

Here's what I've replaced so far:
Coolant Temp. Sensor
TPS Sensor
Battery & Alternator (not really related, but needed to be changed)

Only things I can figure are the injectors. I know these cars are known for having crappy injectors.

Please help... I'm just about to my boiling point with this car. Thanks in advance for the help

 

When you replaced the TPS did you adjust the settings accordingly?
Plenty of write ups explaining how here

 

Will not having it adjusted properly make it run that bad? It sounds aweful. Like its only running on half the cylinders.

Will the TPS cause it to not start without giving it gas?

Thanks for the reply

 

It surely won't help none. I didn't realize the tps had or needed to be set when I had my intake off and apart and just took the tps off and stuck it back on. But it did help a lot with idle.
When you had the codes ran, did it throw any codes? Or still have any? These tpi engines are mighty touchy with all the sensors, they all need to be in harmony to run correct.
A bad maf will cause it to run horrible, stuck iac valve, are common culprits also.

I'm personally more of a carb guy myself, but have been learning the tpi stuff as I've been restoring an 89 iroc. No expert by no means, but a lot of helpful threads here and members willing to help. I've got the manuals and still have access to gm the gm service/specs etc info anytime. If need any info i can pull it up

Sorry just noticed you have 91 model, so no maf for you

 

It actually threw quite a few codes. Codes for the VSS, TPS, & Coolant Temp. Sensor... Changed all of them. No More Codes, but now it won't run.

Gonna adjust the TPS tonight to see if that helps. Appreciate the help guys. I'll get on here once I'm done and let you know if it worked.

 

Yep, I was in the same boat also, had a few diff codes, including the CTS sensor that I had already changed. But the driver side fan would come on as soon as the engine started running. Had the code 14 CTS, thought wtf its a new sensor. Anyhow i put another new one and and no more CTS light and fan dont come on now until its suppose to.
Theres a ton of things make it not idle right. Id start with the tps settings. I noticed when you set it right it opens up the butterflies just a touch in the throttle body.

 

https://www.thirdgen.org/tpimod2

 

Have you ensured your vacuum is hooked up correctly? Ran into a guy last week with a Trans am with butchered vacuum that has the same issue...

Also egr could be malfunctioning and sticking open at idle.

 

just dealt with a leaking throttle body AKA vacuum leak and had almost the exact same symptoms

 

EGR was removed by the previous owner when he installed the headers.

Does anyone have a diagram of the vacuum lines that way I can check those also? Thanks

 

Iac will cause this. Check first if you somehow disconnected the wires under tb. If not replace it. When iac is bad it wont idle without gas and wont start without giving gas. Check it out let us know.

 

It's FIXED!!

Cleaned the IAC and adjusted the TPS.... Fires right up on the first try. Can't believe that the TPS being out of whack can cause that much trouble.

Just want to say thanks for everyone that posted for the help. I'm excited to have a third gen again. I was starting to lose my excitement for the car. Hearing that car fire up again brought it back. Thanks again guys

 

Cool, i have found these tpi engines are mighty sensitive with all the dam sensors. 1 gets out of whack, can be a pain in the old cod sack.
I would never known the tps needs adjustment if not for this website. I just pulled mine off and put back on never thinking about it and it wouldn't run hardly either.

 

If you ever get into tuning, you will see why the TPS has so much to do with how the car runs.

Glad to hear you got it sorted out.

 

Well, Unfortunately, I'm back!!! Car ran great for a couple of days. Started it up to move it out of the garage. Ran fine. Cleaned out the garage, hopped back in it to pull it back into the garage and it stalled.

Went right back to what it was doing before. Won't start or stay running without giving it gas. Checked the TPS signal. Right on where it needed to be.

The only thing I can think of is that maybe the IAC valve really is bad. That's why it will run great for a bit and then out of nowhere, start running like total crap.

Please help me with this... I'm frustrated beyond belief!! And now the wife is too cause it has to stay in the garage because it wont run.

Thanks for the help, guys

 

Take any car and unplug the iac and start it up. It will die without giving it gas. I would remove iac housing and carb clean all the carbon out of it so the new iac you buy, the pintle has a new seat to seal against. Seems like the iac is suspect.

 

Where are u located? If your close by I think I have a few spares in my garage. If not when you do swap it , thread sealer on threads and new iac gasket, make sure connectors are clean and contacting also.

 

No codes on the computer?

 

I'm located in Tulsa, OK... Not sure how close that is to you.


Hopefully, I'll have time this weekend to pull the Throttle Body, clean everything again, and replace the IAC. I'm running out of option as to what could be causing this.

The one thing I did notice when it was running is that it seemed to be idling pretty high and running pretty rich. I have the typical "broken tachometer" so I can't tell exactly what rpm I'm at, but i know it's higher than it should be.

 

Is the car completly stock? Did you remove anything manifold wise? Vacume hose condition? Did you try to adjust the throttle plates at all? Tps sensor can be adjusted. If off this tells the ecu the car is reving or accelerating if open more than idle. When you set the tps you adjusted it by way of turning it and seeing voltage not by turning idle plate screws? Running rich could be fp set to high and on cold start car is still in open loop and never gets into closed loop because it cant idle long enough. How new is o2 sensor? You can bench test these if its suspect with a torch. If you are getting a iac get a well known brand. I stay away from autozone or advance electronics. How soon you going to fix this? I can mail you one out to try as I know a good name brand one is almost a 100. Take care.

 

Car isn't completely stock. Has Hooker Headers. The EGR has been removed. It has a Chrome Timing Cover so I'm gonna assume that the cam has been changed at some point. If not, that's a lot of work just to have a shiny timing cover.

I turned the TPS to adjust it to .54V

I haven't checked the Fuel Pressure yet. That's definitely on my list though

I'll take a look at the O2 Sensor.

I'm planning on fixing this over the weekend. That would be great if you could send me one to test it. How much do I owe you for that, man?

Thanks for the help. Can't wait to have this thing up and running good so I can actually enjoy it.

 

You dont owe me anything. Consider it help. Just pass it along. Ill see what I have at home after work. Egr wont affect anything. Cam maybe was changed. Factory chip in the car? Its blue.If you have an adjustable regulator someone may have adjusted it wrong. But if everything was running fine then the car crapped out most likley its a sensor. Did you do the paper clip test on port?

 

Pm me your address Ill mail one out tm.

 

PM Sent.

 

Old thread, but everyone still has the same problem. At one time my Camaro would not run unless I had my foot on the throttle. Sometimes it would stay running after I lifted my foot, sometimes not. Another day I would have no problems at all. Iac valve had what looked like sealant on the end of the pintle. Cleaned it off and the problem was fixed. Other problems arouse later down the road, but not because of the Iac.