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Registered
Join Date: Aug 2020
Location: Calgary, Alberta, Canada
Posts: 3
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1984 911 - Cold Idle Issues
Hi everyone, this is my first post! I have been chasing a cold idle problem with my 84 911 for a couple of years, so I'm hoping someone may be able to help.
Here's the problem. When the car is cold (after sitting overnight), the car starts, goes to high idle, and then as it drops to normal idle the RPMs slowly drop until the car stalls. It is often difficult to restart. After about 10 minutes of driving, when the engine reaches normal operating temperature, the idle is normal (around 850 RPM). Driveability is good/normal, however occasionally when the car is at normal operating temperature, the car will stall when the clutch is disengaged after a long period of sustained driving. The car restarts without issue on these occasions. I took a video that demonstrates the behavior: https://www.youtube.com/watch?v=47ngq5EGqcc I've take the following actions which have had no effect on the issue: Air System • Idle Stabilizing Valve replaced • Oxygen sensor replaced • Throttle body inspected – butterfly clean and closes fully, general condition very clean • Air Flow Meter removed and inspected – gate clean and moves freely, general condition very clean • All vacuum lines checked, no cracks or leaks found • Ide speed adjustment screw removed and inspected – clean condition • Rubber boot between AFM and throttle body removed and inspected – clean condition, no cracks • Air-to-fuel ratio and idle speed adjusted Fuel System • Fuel filter replaced • Fuel pressure regulator replaced • DME relay replaced • Fuel pump relay replaced • DME inspected and rebuilt Ignition System • New spark plugs 8k km ago • Distributor rotor and cap replaced • Spark plug wires replaced • Ignition coil replaced Instrumentation • Cylinder head temperature sensor tested – OK • Throttle position switch tested – OK • Throttle microswitch tested – OK • AFM temperature sensor checked - OK Any thoughts/suggestions/ideas would be very welcome as the cold stalling issue makes the car very difficult to drive in the first 10 - 15 minutes of city driving. |
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08-29-2020, 07:02 AM
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Join Date: Oct 2017
Posts: 9
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I have a similar cold temp/poor running condition. Did you get any replies to your post?
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10-17-2025, 07:02 AM
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Check that the ICV is getting signals from the DME. I had a transistor burn out in the DME which caused similar problems. Test the ICV on the bench. Make sure it opens and closes easily. You can do this with a power supply. Ground is the middle connection. Touch 12v to either the left side or the right side (not both at the same time) and watch for the valve to open or close. Now apply 12v yo the other side and the operation should reverse.
Next, open the ICV, then reinstall it on the car but don't plug in the electrical connector. Start the car, then plug in the electrical connector after a few seconds. Does it stall? Now do the same experiment but start with the ICV closed. If the car stalls in either of those experiments you likely have a bad DME (the car may not run with the ICV closed, if not, you may only be able to run the open experiment). |
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10-17-2025, 07:29 AM
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You should also smoke test the intake to make sure you don't have leaks.
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10-17-2025, 07:35 AM
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Quote:
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Gilles RoW 88 Carrera coupé |
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10-17-2025, 09:38 AM
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Yeah, I tried to write this from memory. I'm old, bad idea!
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10-17-2025, 10:36 AM
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Quote:
__________________
Gilles RoW 88 Carrera coupé |
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10-18-2025, 01:31 AM
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88 Carrera coupé
