'86 Idling issues - mine of it's own

[NOH20]

So I did a search on this and found many threads however, no solutions to my particular problem. My car runs fine when first started however once it begins to warm up the idle will increase to 2000 - 2250 RPMS on it's own. I can get the idle to drop back to normal by simply opening the throttle and realeasing it. I can also be driving and engage the clutch and the RPMS will stay around 2000, as soon as I hit the throttle the RPMS increase then decrease down to a normal idle.

My microswitch seems to be OK. I can hear it click, the throttle linkage is not bound. This only happens after the car starts to warm up. Any suggestions?? Kurt V, sounds like you had the same problem back in March. Did you root cause the problem?

Brad
Michigan
'86 Carrera
SSI's
Steve Wong Chip

[North Coast Cab]

Check the idle control valve. While it's running high tap it with a wrench. If it fixes it remove and clean. It may be all you need.

John

[Rot 911]

Brad, sorry I didn't get back to you by PM. My problem had to do with a poorly adjusted idle that was compensating for other engine problems. After I rebuilt the engine my problem was solved by adjusting the idle screw way down.

[Steve W]

Brad, I am certain your idle microswitch is activating intermittently. It is either caused by a bad microswitch, or too tight of a linkage between the throttle body and the pivot at the tranny. If you snap the throttle and it goes to normal, the switch was not closed previously. If the switch does not close, you will remain in part throttle operation, and my chip will idle around 2000 rpm unless the switch activates, telling the DME to access the idle maps and parameters.

[NOH20]

Steve,

What's involved in changing the microswitch? Is this something I can do or is it better to take to the dealer? Any idea on what I should expect to pay for this part??

Thanks,

Brad

[Lorenfb]

You need to check a number of things:

1. Hopefully you don't have a performance chip, if so replace with the stock Porsche
chip. You have the DME selector switch set to the base position (fully CCW).
2. You've checked the fuel pressure, (36 to 40 psi)
and MONITORED it while driving.
3. You've checked the CO at 2000 and the problem point,
S/B about 1.5% before the CAT w/o the O2 sensor.
4. You've disconnected the O2 sensor and tested the car.
5. You've checked for no binding areas in the AFM, i.e.
the flapper is not sticking.
6. You've checked the temp sensor for proper values,
visit www.systemsc.com on the Diagnostics page for values.
You can bypass the temp sensor with a jumper once the engine is hot.
7. You've checked for an adequate spark, at least 20-25 mm from
coil wire. Also check the distributor cap & rotor.
8. You've checked for proper voltage to the DME unit when
the problem occurs.
9. You've cleaned the speed and reference sensors.
10 You've cleaned & tightened all ground connections related to
the fuel injection and ignition systems.
11. Using an ohmmeter, check between pins 2 & 5 on the DME connector.
It shoud read about zero ohms with the throttle at rest. This checks
the idle switch. You can adjust the switch for proper closure.
12. Clean the idle valve and check the resistance between the center
and outer pins, i.e. about 20 ohms.

None: Not all the above may apply, but it's always good to check the
basics.

[Steve W]

Brad, if it's the idle microswitch, it the one pointed to by the pen in this pic, the activating arm stop you can see just above it:

[NOH20]

Sometimes it's as simple as turning a screw. The root cause was a very tight cruise control cable that at times would not allow the throttle linkage to move far enough to hit the idle microswitch. I loosened the cable and the problem disappeared. Only thing is I created another idle issue by making this adjustment. The idle needs to be readjusted since it now reads around 600 RPM. I'll adjust that up to 800-850 this weekend and see if the problem disappears.

Thanks Steve and KurtV for all your help. By the way, my car took second place in a local concours event. I lost first place by 0.2 points!

Brad