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Idle issues...

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crash_out:
Hey all, I'm having some idle issues with my 86 GT. It runs great, just idles erratically.

I've replaced/eliminated every vacuum line, and blocked every open port. The PCV system is removed, replaced by plug in breathers. EGR is removed, and I burned a chip to eliminate it from the ECU. Cold start injector is removed as well. It has a fresh tune up. I've done multiple different vacuum tests, and there are no leaks I can find. Fuel pressure usually hangs around 37-40 psi, and it holds it for a few minutes after cutting it off. Injectors are new as well.

When I crank the car, it'll surge up to 2500-3000, then drop down and quit. If I can hold the throttle for a little while as it is surging up and down, it'll eventually settle down and idle on its own. It'll usually start about 2000, then over a few minutes gradually move down to around 1100. From there it may idle for a few minutes, but will eventually work itself down to 800 or so, when it usually will just quit. Most of this time, there is a lot of popping and gurgling from the exhaust, that will go away under throttle and while driving. I have no cat, and a Borla exhaust. It honestly sounds a lot like my Focus turbo that also has no cat and Borla muffler, and also pops and gurgle, just not as badly or noticeable as the Fiero.

Driving, it runs fine, but will sometimes either quit, or surge back up to 1100-1500 if I engage the clutch at a stop or take it out of gear.

Thanks!

Fierofool:
I'm watching this. I have the exact same symptoms on my 86.  Once it warms up it idles correctly but with the gurgle and pop.  I have to hold the throttle at about 2500-3000 when it's cold until it settles down.

crash_out:
I messed with it today, performing the IAC reset, and the surging settled down a bit. It really tries to idle at 900 after its up to temp, but just stalls out.

It did throw a code for VSS, even though it's on jack stands and not moving. The manual says to ignore it if the it throws that code and is not moving. But, I've read on Pennocks that of the VSS is bad it will affect the idle. I'm hoping I can get the brakes done tomorrow and wheels back on so I can drive it and try to get it all sorted out.

Fierofool:
I replaced my IAC with a new one and there was no change.  Never heard of the VSS affecting idle.  I know it doesn't run worth a darn going down the road if you drop the gear because the TPS and VSS and all the other sensors don't match the tables in the ECM. 

Check the voltage on the TPS.  I found that helped a little when I got mine down to 0.5 volts. 

My car idles at about 900 after it's warm but unlike yours, it doesn't stall out. 

In case you aren't aware, when the car is on a floor jack or jack stands, never put it in gear and run it unless it's supported underneath the control arms.  Due to the sharp angle of the tripot at the transmission, it can bind and destroy the joint, especially on the driver's side but not so much so on the passenger side unless it's an automatic.

crash_out:
Yeah I haven't actually put it in gear while it's been on stands. Just idling if I started it all.  I will connect the laptop to it tomorrow. I think the diagnostic software I have will read out the TPS voltage. I think I had cleaned it already, but I plan on pulling the IAC to clean the passage again just in case.

Later this year I'm planning on starting the 3800 swap, so I'm hesitant to really put anymore money/effort into the 2.8. I'd just like it to be functional in the meantime...

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