88 gt wont idle, stay running (Page 1/2)
Tallguy68 DEC 28, 05:46 PM
I have an 88 GT I purchased this summer and am going through to get ready for spring driving.

I recently did a bunch of maintenance, improvement stuff under the hood. It only has 80k on it (supposedly) and I have been checking things that I thought would need cleaning or replacing from just deterioration. So here’s a list of engine stuff I’ve done:

-replaced vacuum lines with steel ones from Fiero store
- replaced Egr valve
- replaced pvc valve

The issue I’m having is it starts great, but won’t stay running unless I keep it above 2k rpm’s or so. Otherwise it sputters and pops, then dies, if I try and just let it idle.

Since it ran and idled fine before I started the work I assume I did something. But I’ve checked as best I could to make sure all the vacuum lines are properly connected (using mirror and flashlight) to make sure all the vacuum lines are connected and still having issue. It’s possible something happened putting the plenum on, but can’t seem to see what. I’m not much of a real mechanic and if it were carburetor I’d think choke, but it’s not. Duh.

I know this isn’t much to go on, just looking for a direction to try and diagnose. Hoping I need to turn the thingamajig by the whatchamacallit, but probably a little more complicated than that.

Oh, I also added cruise cable that was missing when I bought the car. Can’t imagine that would mean anything here, but….

[This message has been edited by Tallguy68 (edited 12-28-2022).]

Patrick DEC 28, 08:09 PM

Welcome to the forum, Stretch.

Did the distributor get rotated a bit? That would throw off the ignition timing.

What's the fuel pressure? Knowing that would help a lot to diagnose the issue.
Tallguy68 DEC 28, 11:41 PM
We’ll, I shouldn’t have bumped the dist, but I’ll check it against the pic I took before I started. Though I did label and remove the front 3 spark cables to get the plenum off. I’ll definetly go through and double check all that.

I’ll have to figure out how to get the fuel pressure reading if that doesn’t work. I’ll probably take the plenum off and double check my work and make sure my new vacuum lines are all hooked up/not leaking too.
Patrick DEC 29, 12:03 AM

quote
Originally posted by Tallguy68:

I did label and remove the front 3 spark cables to get the plenum off. I’ll definetly go through and double check all that.



It wouldn't be the first time here that someone got the plug wires mixed up.


quote
Originally posted by Tallguy68:

I’ll have to figure out how to get the fuel pressure reading if that doesn’t work.



There's a schrader valve on the fuel rail for attaching the gauge.


quote
Originally posted by Tallguy68:

...if that doesn’t work. I’ll probably take the plenum off and double check my work and make sure my new vacuum lines are all hooked up/not leaking too.



If a vacuum line is leaking, the idle speed will usually be higher.
sdgdf DEC 29, 03:07 AM
The timing being off from shifting the dizzy slightly shouldn’t make it idle that bad. There’s a huge EGR line that goes up under the intake that likes to break and create a huge vacuum leak, have you tried replacing that? Either that or get a timing light and see what happens timing it. It idled fine before and that’s all you changed?
Eliredandblack DEC 29, 03:38 AM
You probably should purchase a 1988 Pontiac FIERO Service Manual. Take a Look at the TPS ( throttle position sensor) on the throttle body, are the wires/connectors going to all the various engine components clean are they plugged on tight? I will assume you are not getting a check engine light?
Tallguy68 DEC 29, 09:50 AM
Thank you guys! Pretty good at finding and replacing parts, not much at diagnostics yet so arrows pointing are a great help

1) going to go through distributor/ cable check first. I’ll take the big “L” fingers on the forehead in exchange for simplicity.
2) will check the throttle body
3) I did change all vac lines with Fiero store kit, so I’m thinking I replaced the big long one. If there a vac leak it’s either at connections or some new place.

Thanks everyone!
Tallguy68 DEC 29, 09:51 AM
Oh - and no check engine light.
ArthurPeale DEC 29, 10:14 AM

quote
Originally posted by Tallguy68:

3) I did change all vac lines with Fiero store kit, so I’m thinking I replaced the big long one. If there a vac leak it’s either at connections or some new place.




they're talking about the EGR tube, it wouldn't be included with the Fiero Store vacuum line kit.

It goes from your EGR valve, right under the plenum.

If it's cracked (and, the originals are likely cracked) it'll cause a VERY high idle.
Tallguy68 DEC 29, 11:04 AM
Actually, the pipe that hooks to the EGR valve did come with the kit. In fact, the fiero store had to send me an extension because, of course, the 88 is a little different.

I have both Chilton manual and Pontiac service manual. I checked the spark plug cables and they’re all hooked up right as well as a quick check of the electrical connectors and they seem ok.

With the low miles and it sitting for awhile, is it possible the fuel filter is clogged? I haven’t even run a full tank through it since I bought it, and I filled it up with premium unleaded and a bottle of aqua foam fuel stabilizer. Again the symptoms are it starts with no problem, but won’t stay running at idle speed. I have to give it more RPMs. There’s a lot of sputtering and popping. so if it’s a vacuum line leak that will make it idle faster, that probably isn’t the problem?

I’ll try starting it again. Once everyone in the house gets up and I don’t disrupt, anybody’s sleeping, see what happens after I jiggle them and pressed in the wires.