Idle Rough After Startup, Then Improves

[sclebo05]

I have an issue with my '81 Spider idling just after startup, and I've gone through some of the guides to no avail.

The car starts great every time, even from cold start. It idles 'high' for a few seconds, then starts to 'settle'. At this point the idle dips WAY down, stutters, and sometimes dies. If I barely give it throttle, it seems to run at about 2000 rpms.
After a few minutes when it 'warms up' while I gingerly give it gas, it seems to settle at about 1800-2000rpms, and never dips down again, but this seems a bit high to me. At this point, the car runs well and never hesitates or shows any other issues.

Things I have tried:
- Verified the Auxiliary Air valve is not stuck
- Tried pinching the Aux Air valve hose to see if that helped (didn't)
- Attempted to adjust the idle settings. Taking the idle screw out stalls it.
- Coolant temp sensor resistance is within spec at hot and cold
- Verified air flow meter is not stuck
- Checked for vaccuum leaks around brake controller, replaced brake controller hose
- Verified cold start injector is spraying fuel on startup
- Unplugged cold start injector (car wouldn't start without it, normal I guess)
- Cleaned electrical connections on 2 front pods, under dash pod, and verified trunk ground.

Any recommendations on where to go from here?

[rlux4]

Sounds like you've done a decent job of diagnostics. I had a similar issue with my 82 and it turned out to be the AFM. It would operate normally after warmed up. Replacing the AFM cured it. Before you go that far though, take the cap off the top of your AFM and see if the wiper tracks shows any visible signs of wear or breaks in the tracks. Maybe a gentle cleaning will help if it's got gunked up. Carb cleaner on a tissue will work. If nothing is visible you could try moving the wiper arm slightly up or down on the center shaft to position the pick up points on a different line of the tracks. Do you have access to a known good AFM to try?
Ron

[sclebo05]

Unfortunately I don't have a spare AFM. My 2nd car is a '75 (so not FI). I'll try to clean the AFM and see if that helps.

[GeorgeT]

Check the "Throttle Position" sensor for correct adjustment. I don't know if it could cause this but it is the only thing I noticed that you did not check.

[sclebo05]

Did a few things, and might have it licked.

- sealed brake booster vacuum hose, didn't make a difference
- Adjusted the TPM, touching the throttle produces an audible click
- removed air box to once again check AFM movement

When I replaced the air box, and started the car ... it ran consistently, at about 500 RPM, with no stalling. Then I realized I had forgotten to plug in the AFM harness. Aha! Took the cover off of the AFM and sure enough, I had two deep groves on the conductor surface, and a bit of buildup at one end. I lowered the arm in the AFM 1/16" and the car started right up, with no trouble. Took it for a quick spin, and seems to be great. It idles at 1500 - 1600 RPM, which is 500 RPM lower than before adjusting the AFM. I tried messing with the idle screw, but can't get it down too far. Should I still be searching for an air leak?

Thanks for the help, probably fixed my stalling issue when cold.

[RRoller123]

The throttle cable may be too tight, keeping the idle high. (?) Make sure there is some noticeable slack in the cable when throttle is off, then adjust with the screw.

[sclebo05]

Dah, I spoke too soon. Throttle dips terminally unless a bit of throttle is applied. Back the drawing board...

[sclebo05]

Replaced the AAV, wasn't convinced the old one was moving quite enough. Still have the issue, but I'm eliminating causes.

[RRoller123]

I have the exact same problem, and have checked many of the same things too. I am replacing the connector at the Water temp T sensor, and I also need to examine the exhaust manifold closely for any leaks along its length. When warm, it expands and might be closing a small leak (it is a little noisy) which could explain it. I would be very interested in the ultimate solution you find to this problem, because it is a bugger!

[sclebo05]

The car seemed to develop a new and scary symptom - completely dying while driving. Twice the car died, and I was able to coast to the side of the road. Suspecting that I ran out of gas, I was surprised to find that I still had plenty. After 15-20 minutes, the car started up and resumed as normal. This had me thinking in new directions.

Three things that I performed last Fall that seemed to have helped:

1) Removed the gas tank, cleaned the inside thoroughly, and repainted.
2) I replaced my fuel pump AND filter. The filter was ... filled with mud, from the tank.

And finally, the one I suspect did it ... 3) I replaced the double relay. After reading other posts, this seemed like a worthwhile replacement, as the car seemed to have an original. With these three changes, the car has never run better.

The car now starts and maintains idle when cold.