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Join Date: Jun 2001
Location: Kent. UK. 944s2--'89
Posts: 354
Tickover fall & rise

Hi, sorry to bother you folks again but one issue solved, another arrives. The car ticks over ok when cold but when warm drops from 850 to virtually nil then back to 850 then down again, and repeats this. Every time I stop at a road junction it feels like the engine is going to stall, itís a worry. I have cleaned the air control valve under the manifold but the problem is still there. What other options are there please?

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Old 10-01-2020, 07:52 AM
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Replace the Digital Idle Stabilizer (air control valve). They wear out.
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Good luck, George Beuselinck
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Old 10-01-2020, 08:04 AM
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Thanks for swift reply, that surprises me, as I was under the impression the acv (under the manifold) only came into play when engine cold. However you know better than me!
Is there a test before I pay out?
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Old 10-01-2020, 08:22 AM
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On the early 944s (82 to 85/1) the air control valve was to boost the airflow (and the idle speed) when the engine was cold. Starting with the series 2 cars, the DIS is used all the time to adjust the idle speed to spec, no matter whether cold or hot.

The DME pulses the voltage to the DIS, adjusting it on the fly, based on the speed it detects and whether or not the throttle position sensor is a idle position. You can test the DIS out of the car, using battery voltage and observing the location of the rotary valve. It could just be sticking, and a good cleaning with brake cleaner might help, but you said that you already did that, hence my diagnosis.
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Good luck, George Beuselinck
www.944ecology.com
Porsche Deconstructor (tm)
We buy 944s and sell 944 parts (845-379-1944)
We rebuild torque tubes and instrument clusters for 944/968/928
Old 10-01-2020, 09:20 AM
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Thank you, thatís interesting and in view of that, Iím happy to see if a further clean out and test will do the job. When last done I noticed the rotary valve was partially open as default, I presumed this was correct. From memory the my valve has 2 electrical connections, my understanding is some had 3.
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Old 10-01-2020, 09:37 AM
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Also make sure that your TPS is "clicking" when you let off the gas pedal.

There is some programming in the DME to ensure that the engine doesn't stall when coming off throttle, and if the TPS switch doesn't engage, you can get stalls or very low idle like you described.
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Old 10-01-2020, 09:55 AM
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I have checked TPS but thank you for the thought, I’m grateful to all, for possibilities.
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Old 10-01-2020, 10:00 AM
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After an unfortunate delay, I have now cleaned the acv again and checked as suggested, it clicks and operates when flashing 12 volts across the contacts. While itís off, can I can just connect the electrical plug to see if there is the necessary 12volt pulse from the DME and see if the valve opens, and if so I presume this action should occur with just the ignition on, rather than the need to have the engine running? Thanks for your consideration.
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Old 10-15-2020, 10:56 AM
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Well Iíve answered my own question, connecting the valve prior to fitting, then turning the ignition on, nothing happens but when spinning the engine over you can see the valve open. Iím now accepting the valve is working. The TPS is switching ok when starting to move the throttle.

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Old 10-16-2020, 09:07 AM
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