2.8 idle speed when cold too high (Page 1/2)
Kitskaboodle JAN 06, 07:56 PM
What is the “normal/average” idle speed for the 2.8 when cold? I have an 85 GT and an 86 GT (both are auto’s) and the idle speed is vastly different between them. My 86 idles around 1200-1300 at fast idle but the 85 fast idles at 2500. 🙁
2500 is just too high. I don’t recall it doing this until recently. One culprit (and this is something that I did) is that I had a terrible time with the egr solenoid not behaving right (Nox was very high and the egr was not opening very much or at all) So, in order for it to pass emissions, I plugged the vacuum line going from the air cleaner box to the input side of the egr solenoid. It passed awesomely! In fact, the Nox was practically zero!! Anyways, I decided to leave it plugged and see how it ran plugged all the time. It runs just fine except for the slightest bit of hesitation accelerating from a stop. Otherwise, it drives just fine. I mention all this in case this is what is causing my high idle when cold. Once its warm, it goes down to about 1000-1100 or so.

Is there any way to lower the fast idle when cold?
Kit

[This message has been edited by Kitskaboodle (edited 01-06-2024).]

Stingray92 JAN 06, 08:07 PM
It's been a really long time since I had been in a V6 Fiero, if memory serves me right I would have thought it would be around 1400-1500. When it got ice cold it would be up a little higher for a few minutes. I suspect you might have a vacuum leak.
Raydar JAN 06, 08:47 PM
As you may have figured out, the line from the EGR solenoid to the air filter is a "bypass" line. When the EGR isn't being commanded "on" by the ECM, the ported vacuum from the throttle body is diverted to the "outside" by the solenoid. This ported vacuum is connected to that line, instead of being directed to the EGR valve.
By plugging that line, you have ensured that any time there is ported vacuum at the throttle body, the EGR valve will open. I might be inclined to just unplug the vacuum line from the EGR valve, and cap it off - the line, not the valve, although you could do both.

With all of that said, I really doubt that it's going to make a big difference. But it will take it out of the equation for troubleshooting purposes.

Edit - If you can lay hands on a scan tool, look at the Intake air temp and the coolant temp. If they're drastically different (colder) than what they should be, it can cause your idle to be high, as well as making it run rich.

[This message has been edited by Raydar (edited 01-06-2024).]

Patrick JAN 06, 08:48 PM

quote
Originally posted by Kitskaboodle:

Once its warm, it goes down to about 1000-1100 or so.



Warm idle should be 900 RPM. If your tachometer is correct, I suspect you have vacuum leak(s).

[This message has been edited by Patrick (edited 01-06-2024).]

1985 Fiero GT JAN 06, 11:04 PM
Likely the EGR tube, that commonly cracks, which causes an idle increase anywhere between 1000-3000rpm or more, especially when cold, my Fiero has a cracked EGR tube, Cooke idle was 2500, which very slowly went down to 1000, never thew the idle speed code except for once in 12,000 km of driving, because as the EGR tube heats up, it will seal itself slightly more, and there is just enough overhead in the idle air control to dial the idle down to 1000 or so, but that is with the computer pretty much turning the idle air entirely off, with all air coming in through the EGR tube. The common place that they break is at the very top directly underneath the intake manifold, when I removed mine, it ended up coming off in 2 pieces, I had done wrap over it that was just enough to keep the idle speed ok.

If it isn't the EGR tube, there are not many things that can cause a high idle like that, brake booster line is another that could potentially cause high idle like that, most other vacuum ports are to small to do that much, but most common failure is EGR tube
Patrick JAN 06, 11:40 PM

Lots of good info in this thread... High idle problem, unable to solve
Kitskaboodle JAN 07, 11:00 PM
Thanks for all the replies.
I’m kinda thinking the high idle is indeed from the egr being open fully when cold. I know I don’t have vacuum leaks because the idle
settles down to acceptable levels.

At any rate, it comes down to two choices: remove the blockage from the air cleaner to egr in let port hose (but in consequence knowing that I’m spewing out very high Nox into the atmosphere) or disconnect the vacuum hose to the egr valve for the first two minutes of start up when cold, then plug it back in. Yes, this would get old kinda fast.
Kit

[This message has been edited by Kitskaboodle (edited 01-07-2024).]

Kitskaboodle JAN 07, 11:05 PM
Thanks for all the replies.
I’m kinda thinking the high idle is indeed from the egr being open fully when cold. I know I don’t have vacuum leaks because the idle
settles down to acceptable levels.

At any rate, it comes down to two choices: remove the blockage from the air cleaner to egr in let port hose (but in consequence know that I’m spewing out very high Nox into the atmosphere) or disconnect the vacuum hose to the egr valve for the first two minutes of start up when cold, then plug it back in. Yes, this would get old kinda fast.
Patrick JAN 08, 03:19 AM

quote
Originally posted by Kitskaboodle:

I’m kinda thinking the high idle is indeed from the egr being open fully when cold.



No, it's not that. Your engine would run like crap when you started it. This is my experience with a wide open EGR valve.
Kitskaboodle JAN 08, 10:03 AM
After work today, I’m going to remove the egr valve vacuum hose before I start it and I will report back this evening if it changed the fast idle or not.
Kit