944 Engine Revs Problem

[markyboy944]

Guys , I have a 1989 944 S2 (cab)

The car has developed an intermittent problem, (which is now so common,it's un-driveable).

Basically , when you put your foot on the gas , the revs climb very erratically, and often fall virtually to 1000 rpm (even though foot is hard on the gas).

It is erratic, and picture if you will , rev counter jerking from 1000 to 7000 in several "flicks" (i.e. not smooth), then when it reaches the top it falls off .

Actually, when its at 1000 , it's not smooth .. the car occasionally will flick back up to high (or high ish) revs, and also misfires , so the behaviour is kind of random (but certainloy, as mentioned, car not drive-able).

Interestingly, when the problem first started, it was there when I started the car, but then after it warmed up the problem became less and less, then dissappeared(in the first few days anyway).

Now warming up has no effect.

I'm thinking, therefore, that the problem is something to do with some sort of sensor or something ? (I guess I'm pretty convinced that it isn't a physically "blown" engine or anything like that, simply because during those first few days, after warm up, it was 100% healthy, responsive, and revvy.

So - Guys, - any ideas on where I might start to look ?

Many thanks in anticipation

Mark

[S4hounddog]

I'd first check the ignition system, specifically the coil. If that checks out test the throttle position sensor

[markyboy944]

Hi S4hounddog - thanks for the reply.

I think I know where the coil is. Question is - how do I "test" it (!)

Also - where is the Throttle Position Sensor ?

Thanks very much in anticipation

Mark

[Icey1174]

Sounds like it could be a problem with the Mass Air Flow Sensor. Clark's Garage Home Page has a write up to check it and there are a couple posts on here and a youtube video on rebuilding the MAF yourself. It looks like a pretty simple process. As described in the video, the needle that rides on the resistor strip in the MAF wears out the resistor strip. The video shows how to readjust the needle to a new part of the resistor strip that has not been used. Other that have used this method have reported great success.

I am guessing the "Throttle Position Sensor" to be the same thing as the MAF. The MAF is between your air box and the intake manifold. Your throttle cable turns the cam that turns the needle within the sensor.

[Grandad#3]

Hi Mark, Here is the AFM Fix from ytube. I hope it helps out.

YouTube - Rejuvenating a Bosch Motronic Air Flow Meter

Cheers,
Larry