I have had a similar issue hit my car:
Quote: My 944 has bee quite dependable as of late. It is a good job really since it became a daily driver with me putting on more miles in 6 months than the car covered over 5 years.
However it seems it may have taken its toll. A short while ago now and again on rare occasions (it used to do it more when cold ) the car will idle OK (if I am honest, it would stumble a bit more, and hunt slightly the longer it was left to idle), yet when it came to revving the car it would not rev beyond 2krpm. This would soon clear itself with business returning to normal (idle is generally very steady on this car, and it pulls well), although sometimes it would idle at closer to 2000rpm for a short period of time before settling back to its normal idle within 15 seconds or so.
Today this problem came back to haunt me twice, but regardless of engine temperature. This time the car was barely idling, with revving it causing no change in RPM but for it to attempt to cut out, and at one point it did just stumble and die. I restarted it and within seconds the issue went away. When it was close to dying with no throttle I noticed that the boost gauge went close to 1 bar, indicating that very little vacuum was present (at idle it tends to set at or lower than 0.4 IIRC).
It even did it today on the motorway. From what I can tell, the one consistent thing with this issue is that it occurs when I got from no throttle to throttle (be it pulling away slowly, or accelerating on the motorway).
I was thinking along the lines of AFM or TPS, but I cannot see how it would tie in with a change in vacuum.
It has been suggested either the AFM or Fuel Pressure Regulator is at fault.
A new AFM is £400+. There are firms who recondition your current item including FrazerPart (£220 delivered to your door) although they take 5 working days to refurbish your existing item. Alternatively, Design911 also sell refurbs off the shelf, for the same price, but they can get them from their supplier within a day. Of course, there is a surcharge to pay with Design911 until your old unit is returned.
Depending on what is causing my issue (It's now gone to behaving itself again!) I shall let you know if I do go for a recon AFM and what changes it make. My thinking is whilst a MAF would be great, I would rather sort a couple of other small issues with the car to get it to the standard I want, and that a fresh AFM should still be alot better than something which is worn and now over 20 years old. Saying that, I may be keeping my eyes open for a MAF going by how many people are impressed by the changes.
How I do love intermittent faults.
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