Engine randomly cuts out, tach drops, after sitting in cold weather
 

Hello. I'm having a really irritating problem with my recently purchased '83 944 stumbling and cutting out... It starts up and seems ok at first, but I get going down the road and it will stumble or cut out, and the tach needle will rapidly drop (there's no way that the engine is really slowing down that fast). Sometimes the engine will come back alive and the tach needle will fly back up to where it should be. It's hard to say for sure, but I have a suspicion that this is related to throttle position, as it seems like it usually happens when I am slightly increasing throttle; letting off of the throttle seems like it may help it come back to life, but I'm not 100% convinced. It will sometimes die at idle too. I would normally suspect TPS, AFM and/or fuel pressure, but I don't know of a way that those would cause the tach to drop so fast.

It has been cold here in Colorado and this problem seems to be temperature related... Every time that this has happened, the car had been sitting in the cold (below freezing) for several hours. But if I try it again after it has been sitting in slightly warmer weather (40-50 F) for a few hours, it drives perfectly except for a little stumble at 2000 rpm when increasing throttle (it's fine when holding steady throttle through 2000 rpm; it just doesn't seem to like more throttle at that spot). I re-tracked the AFM the other day in hopes of fixing the 2000 rpm stumble and the 5000 RPM cut that I was experiencing... the 5000 RPM issue seems to be a lot better now (maybe not 100% cured though), but it didn't change anything else.

Any ideas?

Thanks

Check the ends of the large rubber boot that goes from the AFS to the throttle. Could have come off or loose on either end. Follow the large tubing that comes off of the bottom also. Could come loose from the brake boost or a couple of other places too.

Next is to check for voltage at the coil IF it will not start after one of these incidents. If there is no voltage at the starter then suspect the ignition switch.

had same problem
 

This is a simple fix, although somewhat expensive. My 87 944 would do the same when the weather turned cold. You could check the distribtor and/or the rotor. Also the coil. After I changed my distribtor cap/rotor, wires coil and plugs my problem stopped. I also added a throttle responce cam which increased my preformance/throttle responce.
Good luck...

Check all the above but I'd suspect the DME temp sensor. It's failing and lying to the DME. And, when was the last time the o2 sensor was changed?

I do hope you know about Clark's garage. Some of the best help ya can find. Getting yourself the FSM will also be of great use.

Good luck, and keep coming back with questions. Do your homework......it will make things MUCH easier. :)

Clark's garage

What about the speed sensor - isn't this what tells the tach how fast the engine is turning also?
Check the plugs at the back of the engine for the speed and reference sensors.

i'm with stoopid ^

oops, i mean, i'm with brad, sounds like a speed/ref sensor connection is loose. check the two connections on the top rear of the motor. they are three pronged connectors, make sure the wires are in good shape and that they are making good connections. i think this may be your problem... if it's not the wires, it may be the sensors. either way, i'm convinced that is where your problem lies.

The reference sensor that sees the single pin is what drives the tach and the ignition at start up. The speed sensor is used by the injection system to set the injector open duration. I know it doesn't sound right.