Maybe some sort of a vacuum leak, or your AFM?

I checked the AFM out per the procedure on Clark's this morning and it checked out fine.

I also tried the O2 oxygen sensor test and got mixed results. The voltage seemed to be on the low end. I could not get it to go above .5 volts.

I could only conclude one of two things:

1. IF the O2 sensor is good the engine is running lean and not getting enough fuel.

2. If the O2 sensor is bad it is not sending a rich signal to the DME.

But I didn't have a proper propane injection system, just something I rigged up using an old tabletop grill valve.

I also opened up the DME to see if I could find any obvious signs of problems and to tell you the truth it looked to be in near perfect condition, the solder joints, circuit boards, etc.

I am stumped...

Popping under acceleration generally indicates a lean condition. Despite your test results on the AFM, I would be inclined to do the procedure to relocate where the wiper arm of the AFM intersects the resistor track.
Air Flow Meter (AFM) - from "The 944 Motronic DME" by FR Wilk* ©2001 www.the944.com

Yes, I popped the cover on the AFM and made the adjustment. It doesn't seem to be helping. The idle is still very rough.

Also opening the AFM door a little forces a rich condition and showed the O2 sensor voltage going to above 0.9 volts, so the O2 sensor seems to check out.

If someone adjusted the spring tension on the AFM, it could still be bad even though it is testing properly per Clarks Garage. I had this problem, in my case it was a rich condition, but if the spring tension held the door shut too mich, it would be lean. The spring tension should never be changed, but I had a mechanic do it to me.

Also could be a vacuum leak causing it to have an intermittent rough issue. possibly on the J boot. I would recommend pressure testing the system and seeing if you find any leaks.

Good luck.

All indications point to a lean mixture based on the O2 sensor testing. It seems to me the injector pulse is too short like it is not using the fuel map. The symptom is a rough idle and no power under load. Could this be a DME problem, a fuel pressure problem?

I guess I will hook up a fuel pressure tester today. In the mean time does anyone have any thoughts on how to further diagnose a DME or do I need to get a known good one and swap it?

I have done a bunch of things to this car over the last few months chasing this problem. First it was bad spark plug wire causing a miss on one cylinder (wire went bad because of ICV hose pressing against it, my fault). Once fixed it shortly became a miss on all cylinders prompting replacement of a bunch of original items such as FPR, throttle switch, DME temp sensor, also the coil, cap, rotor. I could have done something wrong and made this problem worse, I guess. At first it would only do it occasionally, but now it seems to do it after warm-up every time.

After I put another DME in last Saturday it was still doing it. So I cruised around and stopped at a couple of shops for advice. Mostly the advice was to take it to a european place and to get it on an engine analyzer. What the heck, so I took it to this european specialty place about a mile from the house (the porsche specialty place is 12 miles and I was afraid to drive it that far)

When I dropped it off it was doing it (running like crap) and the mechanic noted this. He said he had to hear it running cold to rule out a few things (remember it only does it when it is warned up) The last 3-4 time I had driven it the thing did it within 2 miles of cold startup. The mechanic takes it out 4 times and runs it in 2nd gear and still can't get the car to do it. We did get a cold snap so the weather was in the 20's, so do I have to wait for the spring thaw? But to boot, this place doesn't even have an engine analyzer and the best he could offer me was to do a smoke test to check for air leaks in the intake manifold if/when he could get it to do it.

At least he does offer the advice it is not likely a fuel system problem because it runs OK cold. And this is with a swapped out DME I got from my buddy Just Joshin Porsche 944 Parts in Boonesboro, MD.

Suggestions accepted.