993 fast idle problem persists...
 

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

did you clean the idle valve from dirt??

Yes
 

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

EPS

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.

Thanks
 

Thanks Bill. Will do.

EPS

Test completed
 

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

Bill is impressive about knowledge(thanks)

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

Solved
 

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

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"IT USED TO BE A BUICK..."