Troubble at constant speed below 3000rpm

[Magnus_944]

My 83 944 is not very nice to drive at constant speed if the rev is below 3000 rpm. It feels like the ignition is switched on and off and the car ends up in an oscillating motion. If I start to accelerate, or the road starts going uphill the problem disappears and the engine works fine.

Idle is something like 1200 rpm (not normal? how to adjust?) and the car is easy to start.

Can somebody tell me what's wrong?


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[Pilot_951S]

The idle is way high (suppose to be 900rpm) you may have a vacuum leak somewhere. Check all the hoses that run to the intake system and see if any are loose or cracked.

[Lawrence Coppari]

Once I had the idle adjustment screw completely back out of its seat. It caused the idle to be way too high.

I agree with Pilot 951S, it sounds like vacuum to me. At high load, lots of air is coming in so a leak would have a tendency to be dwarfed by the large amount of air entering where it is supposed to enter. At light load, it is more significant and screws up the mixture more.

[This message has been edited by Lawrence Coppari (edited 07-10-2000).]

[Pilot_951S]

For those who don't know, the idle screw is located on the throttle body just after the throttle plate.

As it happens mine blew completely out recently and caused a high idle and the vacuum leak caused the revs to drop more slowly than normal. Also I have a friend with a 944S and he also is missing the idle screw. I bought a new one from the local dealer for $7, don't let them try to sell you an entire throttle body, the screw is available separately.

Oh and your low RPM problem sounds like a much bigger vacuum leak than the idle screw.

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The shortest distance between two points is in my car.

[tirepro1]

Does it vibrate only at constant engine speed? If so, you might also check the balance shaft belt.