1983 944 AFM Troubleshooting (Won't Stay Running)

[Michigan944]

Hey all! Looking for some second opinions on some troubleshooting I've done on my 1983 944 over the past couple of weeks. I was driving home from work when after about 5 miles the engine fell on it's face after shifting into second. Kept on surging like it wasn't getting fuel, put the transmission in neutral and it idled just fine. Ended up getting a tow home and tinkered with it some.

The engine would start and idle smoothly. If I gave it the slightest amount of fuel I could get it up to 2000rpm before it sputtered and died. Started looking for a vacuum leak with starting fluid but didn't seem to find one. Referenced Clark's Garage next and tested the TPS. Looked like the TPS was not reading the way that it should. Just got the new one installed today and the problem is still there.

I just got done taking apart the AFM and following Clark's instructions on testing, cleaning, and adjusting and wanted a second opinion on the results that I saw. Clark mentioned that with 9V battery he was using (9.41V) he was getting a reading of 0.46V with the barn door closed and 8.45V with it fully open. (Delta of about 9V at closed and 1 V when open).

When I tested mine with a brand new 9V battery (reading 9.7V) I got a reading of 0.16V with the barn door closed and 7.9V with it fully opened (Delta of about 9.5V at closed and 1.8V when open). I cleaned the track and adjusted the arms so it wasn't on a grooved section of the resistor array and the measurements were basically exactly the same.

Would anyone agree that the lower voltages i measured from the AFM could be an indication that it's bad? Especially considering the voltage source I was using had a higher input voltage than the battery Clark used in his guide.

Open to any thoughts or suggestions! Thanks!

[944 Ecology]

Don't overlook the electric connection at the AFM. Over the years, the terminals are subject to fretting, resulting in a loss of signal to the ECU.

[Dano944]

Vacuum leak? Get a smoke detection test done.

[Michigan944]

Thanks George. Are you talking about the terminals on the AFM itself? Or on the connector side?

Another 944 owner recommended that I check to make sure the timing belt hadn't jumped a tooth and turns out that it did. I was already planning on replacing the timing belt and had all the parts for it. Went ahead and did that yesterday but the behavior is still the same. Fires, but sputters and dies right away. I got it to run on some starting fluid shot into the throttle body, so I'm thinking it's got a fuel issue. I'm going to collect the parts to make an adaptor to get a pressure gauge on the rail so I can see if i've got a bad pump, regulator, damper or a clogged filter.

[944 Ecology]

Originally Posted by Michigan944

Thanks George. Are you talking about the terminals on the AFM itself? Or on the connector side?

On the connector side. The pins are a two sided friction fit over the single pins in the AFM and can spread apart, causing an intermittent loss of continuity.

[arabalarca]

Those numbers by themselves don’t really condemn the AFM.

The “fully open” voltage being lower is usually just the wiper not reaching the end of the track / mechanical stop differences, or meter/battery/load differences. What matters more is that the output changes smoothly with no dead spots or dropouts when you sweep the door slowly.

A quick check: backprobe the AFM signal on the car and watch it while opening the flap—if it jumps/flatlines right around the point where it starts to stumble (~2k), then the AFM is suspect.

Given your symptom (idles fine, dies with light throttle), I’d look hard at:

Fuel delivery under load (pressure/volume, clogged filter, weak pump, bad regulator/damper)

DME relay and grounds (common on 944s—can run then cut out)

AFM plug/connector pins and intake boot cracks

If you can post fuel pressure at idle + while revving (or when it starts to die), that’ll narrow it down fast.