Porsche Repair: porsche 944 problems, vacuum hoses, airflow sensor

Question
Regarding my 1986 944. There is a backfire/popping sound when up-shifting, just as I let the clutch out and changed gears, especially if driving hard. My mechanic says the timing is OK. I try adjusting the fuel and air with an allen wrench beside the airflow sensor, no luck. The engine also seems to have little power in the lower rpms and does not rev-up smoothly when starting off through 1st and 2nd gear. When in neutral it seems to rev ok without any misses. Also, just lately with the cold weather, the engine failed to start after sitting for only 30 minutes after running warm. It would turn over strongly and consistently, just wouldn't fire. At the same time I never smelled any gas. It would turn over until the battery dies. No smell of gas, and not even a hint of firing. Could this be an electrical problem? Could the backfire/pop and the not starting all be related? Where should I be looking for problems. Thank-you, sorry for the lengthy explanation.

Answer
Hi Alberto,

Sorry this response has been delayed.  You certainly have a variety of symptoms with each one possibly having multiple causes.  This makes it very hard to proceed in a logical and methodical manner until alll the problems are eliminated.  Two issues that come to mind immediately are:
1.  The condition of the vacuum hoses and the quality of their connections.  A leak or two would certainly account for some of this trauma.
2.  I'd check or have your mechanic check the airflow meter.  Your non-start in the cold could be the reselt of this meter (actually a swinging door) getting gummed up with gunk and oily crud.  If it sends a wrong message to your computer about how far it's open (because it's stuck in the wrong position), the car will never start.

Sorry again about the delay.

Dave