Need advice on Odd Engine Idle Problem

[RRoller123]

I am wondering if someone can point me in the right (obvious?) direction:

My 80FI starts fine, idles smoothly and at higher speed (maybe 1500 rpm) for about 10 seconds as is expected, but then it idles/runs rough and stumbles until it has warmed up for a couple of minutes, when it starts to idle and run fine again. Any obvious things to look for?

Another thing it does after being fully warmed up is that when I come to a red light, the idle drops back to maybe 500 rpm, and then slowly over a few seconds climbs back up to a smooth 1000 rpm, which is where I have it set.

Odd. Any ideas appreciated.

Pete

[narfire]

I had similar idling issues. I found I had a pooched brake booster that allowed non metered air into the intake and I adjusted the AFM arm to a clean section of the track. I set the TPS to just off the full closed position and then set the idle.
Now the car idles at 850-950 rpm and no burbling/ fluctuations/hesitation.

Check for non metered air getting in, aux air valve working properly?
Chris

[RRoller123]

Thanks Narfire. I have done the AFM adjustment, and I am sure the TPS is set correctly (but I will recheck of course), but I am not sure how to check the AAV for proper operation?

And I hope the brake booster isn't bad, is there an easy way to determine that, and is it a PITA to replace?

Pete

[narfire]

but I am not sure how to check the AAV for proper operation?

When the engine is cool/cold, the aav should have a small opening if you look through it. When warm the hole should get smaller to almost a pin hole (mine does) I believe you can check buy sticking the thing in the fridge or freezer for a bit and see if it opens up...should. Then heat and see if it closes. The connection should be snug as well.
I realized my booster was pooched when I had real hard brake application to get the car to stop and a hissing sound down around the pedal. The vacuum hose from the intake to booster would pull outside air in from a probable tear in the diaphragm...note the hissing.

A slight PITA to change... undo the clutch cable at the tranny and I removed the alternator and bracket to make room. I found there is a top and bottom as the fork on the pushrod has to line up with the hole on the brake pedal. I did not undo an brake lines as I could pull the MC out of the way enough. Careful when putting the booster back on as the brake lines could get caught behind the booster.
Hope you get it sorted
Chris

[RRoller123]

Thanks again, that is a great help.

[RRoller123]

The AAV seems to work ok, it looks like this at room temperature (~65degF):



And I put it in our convection oven at 170DegF (the lowest the oven temp would go) and it completely closed after about 10 minutes. No light at all visible through it.

I guess I need to check to make sure the electrical input is speeding this process up. But at least I know that it is opening and closing. It may be that it is closing too slowly, which might explain why the car runs roughly until it has fully warmed up?

Pete

[RRoller123]

So I don't think the problem with the rough running while warming up is due to the AAV. The AAV electrical connector shows 13.15 volts constantly when the engine is running. I think this is correct. Is it supposed to run continuously or does it shut off after a period of time? You fellows have any other thoughts as to what could cause the rough idle until it fully warms up?

[focodave]

Pete,
There is an idle adjust screw right near the TPS.
It points up at an angle toward the passenger side of the car, and it is located just to the rear side of the car next to the TPS.
You could try adjusting that until she idles properly.
Not 100% sure if it will help but is very simple to try and it doesn't cost anything.
Dave

[RRoller123]

Yeah I had set that according to the procedure in the manual, but it was a long time ago. The issue is that the car starts fine, runs well until the CSI stops after about 8-10 seconds, then runs roughly until it is fully warmed up, when it then runs fine. The TPS is set correctly, the AAV seems fine, I had all the injectors serviced, no apparent air leaks, everything seems tight, so I am stumped. But I will go back and readjust the idle as you suggest, it can't hurt! Thanks!

[focodave]

I had very similar symptoms when I installed my new engine.
By adjusting that idle screw out, counterclockwise, it forces the ECU to control the injectors to give the engine a little more fuel.
It sounds like when your CSI stops, the fuel mixture is too lean.
Again, not guaranteeing it will work on yours, but it fixed mine instantly and I just went for my emissions test and it passed with flying colors!
They emission-tested mine at 1000 RPM and 2500 RPM.

[RRoller123]

Excellent! I will give that a shot!

[sclebo05]

Excellent! I will give that a shot!

What was the culprit? I'm having a similar issue.

[RRoller123]

Hasn't been solved yet, but I suspect bad connectors at the water temp sensor and/or the CSI. I am going to replace the connectors by splicing in new ones, but I haven't found them at the various vendors yet. I think they are Bosch. If anyone knows the Bosch part numbers or source for these connectors please sing out! The AAV module tested out fine, and I have replaced cap, rotor, wires and plugs, timed it, and the spark is fine. No apparent air leaks, "rebuilt" the AFM. Had all the injectors sent out and cleaned. New fuel and air filters, new fuel lines. Running out of things to check. Eventually it will make itself apparent.

Runs with really smooth, strong torque and power at all speeds except this damned rough idle.