Idle issues...

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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.

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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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I guess as a way to help others, I can share what HASNT corrected the issue. Of course barring a new component that was bad from the beginning. Also, the car did idle properly initially. I parked it in the garage while I worked on the interior-about 6 months without running. That's when it started surging and stalling.

The car has fresh plugs, wires, dist cap and rotor button. New IAC, fresh fuel, fuel filter, O2 sensor. New injectors. New high pressure pump for my 3800 swap.
I never messed with the timing from when it was running OK.

Fuel system wise, the only not new component is the regulator, and it seems to be functioning. Sensor wise, the the only ones I haven't replaced are coolant, TPS, and MAP. They all SEEM to be functioning. Ignition wise, I can only think of the pick up coil, ignition coil,  and IC module. The exhaust fumes will burn your eyes if you stand back there long enough, but I kind of attributed that to lack of cat and the aftermarket exhaust. I haven't messed with the screw on the throttle body. From everything I've read, there's no reason to unless someone else has messed with it. And I'm not inclined to think that would be an issue since it was fine when I got it.

This kind of leaves only the ECM module. I'm honestly not willing to throw any more parts at it since I'll start the swap in November. If I knew exactly what I needed, I would but that one part. But not randomly throwing any more at it hoping it will fix it.

[Fierofool]

You can check the TPS for correct voltage setting before swinging for a new one.  0.5 Volts at idle position and approximately 5 volts at wide open throttle.  The engine doesn't need to be running.  If it's not at the required voltage, you can carefully bend the tab to get it at the 0.5 volts idle. 

The other thing that I believe could cause the problem, since you say it's running rich enough to burn your eyes and nose, is the coolant temperature sensor.  It can fail without throwing a code.  It can cause the other sensors to try to correct the rich burn by trimming fuel.  Also check the vacuum connections underneath the MAP sensor. 

I think I replaced my CTS.  I did replace the IAC but that doesn't mean that one of them wasn't bad from the get-go.  I think our problem is on the fuel side and not on the ignition side. 

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I checked the tps voltage, and came up with 0.63. That's well within tolerances.  I have a new CTS ,not installed,  but seemed to be getting proper readings through the data port for it. I have gotten the car to go into closed loop as well, which should mean it's getting up to temp. At that point, it really tries to idle at 900, just stalls out at anything less than a rough 1200.

[Fierofool]

If Idle voltage is at 0.63 it's telling the ECM that the throttle is open and thus it's adding fuel.  Could be the reason for the rich burn.  Mine didn't run right at 0.53V.  Adjusting it down so that it bounced between 0.49 and 0.50V did smooth it out when it warmed up.  My fluctuation is while it's in open loop. 

[Raydar]

Sorry. But have to ask... have you verified timing, after using the "short the pins" method to adjust?
 
Whenever I had mysterious idling issues, I removed the throttle body, and removed the IAC and TPS, and everything else I could, and cleaned and brushed everything in the throttle body that I could. I did not remove the throttle plate, but I did clean the bore of the throttle body. Lots of build up behind the plate.
Think I used brake-kleen (red can) and a brush. Also sprayed through all the hose fittings and such. Be careful, Some of those internal passages just loop around. Easy to squirt brake-kleen in your eye. Don't ask me how I know that.

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I haven't checked the timing because I've not messed with it. The car idled fine for the first month or so, then after sitting for several months, it started the issue. I've not loosened the distributor hold down or attempted to move it.

I've cleaned the throttle body thoroughly.

[scottb]

Bad ground?

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I noticed that when the fuel pump primes after you turn the key on, the pressure rises to 45psi, then over the course of about 30 seconds, drops to 20 and sits there. I'm not sure if that's normal. While it's running, it maintains 35-42 psi.
I didn't replace the pulsator in the sender with a pieice of fuel line, I'm kind of kicking myself for that now.
The injectors are all new, and I'm not finding any leaks. I have a regulator rebuild kit. I'm not sure if I'll have time to do it before the RFTH, between a coolant flush, oil change, and shakedown run. I also have a new coolant sensor and oil pressure sender since the original has started to get flaky and will randomly max out and jump around.

[Fierofool]

It should hold the pressure and not leak down.  It's possible that your cold start injector is failing.  Try unplugging it.  It's the injector type connector at the right front of the lower intake manifold, A two wire plug.  Right beside the single wire fan switch. 

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Cold start injector is removed. The holes in the intake and fuel rail have been plugged.