Porsche Repair: 86 928S runs sometimes, sometimes not!, air flow meter, combustion chambers

Question
I have a 1986 928S 5 speed,32 valve. I have owned the car for approx. 6 months most of which the car ran great. The problem is that at times the car will die and immediately restart, and others it will die and hours later it will restart. 1 incident stranded me at work and by the time the car was towed to the shop it fired right up. The mechanic that has done work before on this car is saying that the 12 volts is missing from the injector, and it "could" be the processor/computer. At 900 bucks I cant afford a could. Any help would be greatly appreciated. Thanks in advance Shawn  

Answer
Hi Shawn...

Unless your mechanic is a Posrche specialist who deals with 928's all the time, I'd say it's quite a leap to jump from "it won't start sometimes" to a "$900 computer".  And what happens when the computer is changed and the same problems reoccurs?  Will you get your $900 back?

The problem could be a number of things, but the symptoms you describe are classic symptoms of a dirty greasy grimy air flow meter.  This device is called many things be many manufacturers, but it is basically a swinging doorway through which intake air is drawn into the combustion chambers.  The computer measures how much air is being sucked in by how wide the door is open.  It then takes many other factors into account and squirts just the right amount of fuel into the combustion chamber to get the perfect air to fuel ratio.

Let's say you are driving along and the computer is happy and then you change speeds but the doorway sticks because of crud in the way.  The computer cannot match the door position with all those other factors so it defaults to shutdown instead of wasting fuel.

Most times simply cleaning the accumulated crud will correct the problem, sometimes the unit has to be changed...it's a bit expensive.

Good luck.

Dave