Idle trouble - Time to fess up...

[indigowhale]

Hey Alex, this is from the PCA site, Alan Caldwell:


1. With the engine warm, all electrical equipment turned off, and the oxygen sensor disconnected, first the CO emissions are tested and adjusted to spec (this is essentially the mixture control adjustment on the air box and the adjustment is 0.8% CO +/- 0.2). The oxygen sensor is then reconnected.

2. Then, with the idle positioner disconnected, the idle is adjusted to its spec value using the adjustment screw on the throttle body (800 +/-20 rpm up to 10/86 production). Then the idle positioner is reconnected and the idle speed should stay constant.


If there is still an erratic idle after the above is completed, then one of the following items may be a problem:

1. Oxygen sensor. If it is well past its replacement mileage of 60,000 miles or is not interacting correctly with the mixture control setting and/or idle speed setting, it might be part of the problem. Many oxygen sensors have gone beyond the original replacement mileage without problems, but they can eventually deteriorate. 2. Air leaks in the intake manifold or the hoses attached to the intake manifold. 3. Sticking vane in the airflow mass sensor. 4. Improper fuel pressure 5. Throttle switch 6. Fuel injectors

Of these, the first three are the most common problems. If after that, you are still getting lean running or stumbling after a cold start, I would check the cylinder head temperature sensor which provides the primary enrichment during warm up by increasing the injection pulse time until the engine comes up to full operating temperature. The cylinder head temperature sensor is on the front of the no.3 cylinder and is reached by removing a cover in the engine sheet metal behind the left rear wheel.

Allan Caldwell Website 10-24-01

[THECARREAPER]

Originally posted by indigowhale
Hey Alex, this is from the PCA site, Alan Caldwell:


1. With the engine warm, all electrical equipment turned off, and the oxygen sensor disconnected, first the CO emissions are tested and adjusted to spec (this is essentially the mixture control adjustment on the air box and the adjustment is 0.8% CO +/- 0.2). The oxygen sensor is then reconnected.

2. Then, with the idle positioner disconnected, the idle is adjusted to its spec value using the adjustment screw on the throttle body (800 +/-20 rpm up to 10/86 production). Then the idle positioner is reconnected and the idle speed should stay constant.


If there is still an erratic idle after the above is completed, then one of the following items may be a problem:

1. Oxygen sensor. If it is well past its replacement mileage of 60,000 miles or is not interacting correctly with the mixture control setting and/or idle speed setting, it might be part of the problem. Many oxygen sensors have gone beyond the original replacement mileage without problems, but they can eventually deteriorate. 2. Air leaks in the intake manifold or the hoses attached to the intake manifold. 3. Sticking vane in the airflow mass sensor. 4. Improper fuel pressure 5. Throttle switch 6. Fuel injectors

Of these, the first three are the most common problems. If after that, you are still getting lean running or stumbling after a cold start, I would check the cylinder head temperature sensor which provides the primary enrichment during warm up by increasing the injection pulse time until the engine comes up to full operating temperature. The cylinder head temperature sensor is on the front of the no.3 cylinder and is reached by removing a cover in the engine sheet metal behind the left rear wheel.

Allan Caldwell Website 10-24-01

i have been religiously searching the archives to beat a hunting idle my car developed after i added a bypass pipe and replaced all of the intake gaskets and hoses.

can someone please elaborate on what and where the "IDLE POSITIONER" is that i am supposed to disconnect to set the mixture??

thanks,

Michael

[indigowhale]

Thecarreper:

I added a test pipe recently with no effects, so maybe you frayed a wire on the O2 sensor or it is related to a leak that you cured.

Anyways, the idle positioner is the device that looks like a bid D Cell battery in front of the intake rubber elbow. It has one 1" hose coming into it and one going out of it on the right side and it has a square connector on the left side that you pull off after releasing the square metal clip. When you disconnect this valve, you may notice that your idle quits dancing around a bit--or not.

Anyways, set your base idle spped with the screw right above it, then set your mix using the AFM air/mixture screw. Then, reconnect the wire to it. You will need a digital voltimeter to read the O2 sensor voltage.

Do a search on my handle posts, I can't find it now, but I listed a procedure that I got from Steve Wong on how to set your mixture using the voltage readings from the O2 sensor. It was the only way I eliminated bucking and hesitation which seem to follow the hunting idle.


Best of luck.

[ZOA NOM]

"Idle Positioner" (actually, Idle Control Valve) = red arrow
Idle adjustment screw = yellow arrow

[THECARREAPER]

thanks to you both. the different terminology for the same part is what was confusing me! my 02 sensor has a repair in the wire, so i ordered a new one. i seem to be running a bit lean, but the plugs are old and may be lean from all the vaccum leaks. i lowered the idle to about 800 or so. i dont want to drive the car too much or fiddle with the mixture until i have a good o2 sensor signal. car would stall when cold, and had audible vaccum leaks. now it runs great when cold, but the idle hunts up and down when the car is warmed up to the normal range. from what i read in the archives here, i have a lean mixture issue......