shawscove928s

I just replaced my transmission vacuum modulator and it cured my harsh shifts. But now the idle is at 1100 rpms. The only thing I touched was the vacuum modulator and it's related mountig hardware. Yes I did hook the vacuum line back up to the modulator. I confirmed that there were no vacuum leaks when tracking down the harsh shifts. If I turn on the a/c the idle drops to 1000 rpm. The idle on the car has been 850 rpms for the 12 years I have owned the car.
I searched and searched but this time " search was not my friend"

Any thoughts?

Thanks
Ray

John Speake

A high idle at 1100rpm is usually due to a slight intake airleak. Or could be a stuck ISV or fault LH ECU.

To confirm a vac leak, conenct a vac gauge to the fuel damper at the front of the engine, with car at idle speed, should be about 21" Hg . If it is significantly lower than this, then you have the problem isolated to an intake leak or a leak in one of the vac actuated aux units e.g. heater flaps. You can isolate those at the vac splitter which is under the engine air filter lower housing.

shawscove928s

Thanks for getting back to me John. I have checked vacuum from the trans vacuum modulator and found over 21 lbs there. Also checked under the air box and corrected a leak at the thermal switch. The vacuum splitter and connecting lines all checked out.
Today I will Mityvac check all the lines again just be sure. The high idle only showed up after the replacement of the trans vacuum modulator. So it's probably someting that I disturbed.
I am plannig on testing the ISV today as well. I will have to learn how to check the ECU. (Any shotcuts to check the ECU you may know would sure be appreciated).
This problem falls into that dreaded "928 syndrom". You know "Fix one thing and the 928 will develope another". The 928s are not happy unless their owner has a wrench in their hand.
Thanks again
Ray

John Speake

It may be that having fixed the original problem that going through the WSM CO adjust and idle speed setting proceedure is all that is required....

WallyP

Check the throttle cables to ensure that the throttle is closing completely, and that none of the cables are maladjusted or sticking.

Hanging from the crossbar on a bracket should be a three-pin electrical jack. Two of the pins are close together, with the third separated. Going clockwise, call the two close pins A and B, with the third pin being C. Place a temporary jumper between B and C - this kills the idle speed control. Go down between the first and second intake runners and adjust the idle speed control screw (bypass) on the throttle housing to get an idle speed of 660 - 700 RPM. Remove the jumper. (Page 24-205 in the manual)

If you have the capability to adjust the CO, it should be 0.6 - 0.8%.

shawscove928s

Thank you John and Wally.
As per your suggestions I did try to reset the idle using the work shop manual proceedure. I adjusted the idle scwew all the way to the stop with very little effect only bringing the idle down to 950 rpm. Jumping the B to C terminals on the test port had no effect on the idle speed at all.
Ray

Cosmo Kramer

Either the ISV is stuck open or you have a large vacuum leak. The ISV is there to modulate the idle speed. Jumping B + C disables it, so if it is stuck nothing will happen.