993 fast idle problem persists...

[e p slick]

993 3.6 in 86 911 occasionally (often) is slow to drop back to 900RPM idle after "blipping" to 3000RPM at end of back road driving. I thought it had mechanical interference but does not. 3000RPM "idle" will slowly drop to and stick at 2000/1800 RPM over a one, two, three, four count. If I turn the ignition off and then immediately restart the idle will be at desired 900RPM . The procedure is rather like re-booting computer. I have checked resistance on the three spades of the Throttle Valve Positioning Sensor and the results are perfectly within tolerance. I am inclined to think that although the Throttle Valve Positioning Sensor appears to be functioning properly it is the most likely culprit at this juncture. Before I throw money at what I GUESS is the problem I am curious to know if any of you folks think I am on the right track.
Car does now have Steve Wong chip.

EP Slick - Tucson

[01coccobet]

did you clean the idle valve from dirt??

[e p slick]

Yes, I already had extensively cleaned idle valve. A small bit of residue washed out but still the problem persists.

EPS

Originally Posted by 01coccobet

did you clean the idle valve from dirt??

[Bill Verburg]

you can test the idle valve easily enough, it is a simple push pull device

there are 2 +9v and 1 gnd terminals, 1 +pulls one way the other pulls opposite. Use a 9v battery to test.

The main issue w/ these(besides vacuum leaks) is winding wear around the idle position, you can remove the epoxy from the 3 screws holding the core and rotate the core wrt to the body to have a new idle area. Then adapt the throttle by starting w/o touching the gas pedal. Let it idle for ~ 10min to do the adaption.

[e p slick]

Thanks Bill. Will do.

EPS

Originally Posted by Bill Verburg

you can test the idle valve easily enough, it is a simple push pull device

there are 2 +9v and 1 gnd terminals, 1 +pulls one way the other pulls opposite. Use a 9v battery to test.

The main issue w/ these(besides vacuum leaks) is winding wear around the idle position, you can remove the epoxy from the 3 screws holding the core and rotate the core wrt to the body to have a new idle area. Then adapt the throttle by starting w/o touching the gas pedal. Let it idle for ~ 10min to do the adaption.

[e p slick]

9v test completed. Full open is Full open. Close shows internal shaft going PAST full close and leaving 3/16" + air gap. Should full close actually and literally be "Full close"?

EPS

[01coccobet]

Bill is impressive about knowledge(thanks)

[Bill Verburg]

Originally Posted by e p slick

9v test completed. Full open is Full open. Close shows internal shaft going PAST full close and leaving 3/16" + air gap. Should full close actually and literally be "Full close"?

EPS

I can't find the specs but that does not sound right.

w/ the engine idling pull the throttle pot wire harness, what happens?

ditto, pull the MAF harness

[e p slick]

I have found that the shaft that holds the throttle bell crank on the side of my transmission had a very slight tweek that would occasionally prevent the bell crank from completely returning to a completely neutral position. Once I rectified the problem the idle position always results in proper idle RPM. Never really having had a brain controlled car I couldn't see the forest because of the trees, or snakes because of the politicians or however the saying goes. Once I got back to basics things became more evident. Thanks to everyone who pitched in suggestions and thoughts about my problem. Now if someone can please the meaning of life...


EPS - Tucson


"IT USED TO BE A BUICK..."