azmi951

My 951 is surging and missing BAD. when I disconnect the vacuum line to the FPR it smoothes out at idel. I have not driven it with the FPR disconnected.
Also when it is running and I nudge the AFM door it smoothes out a little.
What says you guys? Bad FPR? Bad AFM?

The weather is really nice in Michigan right now, I was hoping I could drive it.

fast951

Check the line between FPR & Intake, make sure it's not damaged. I would not drive the car with the FPR vacuum line detached, your car will run VERY lean under boost if line is disconnected.

Check the voltage out of the AFM, pin #7 DME should be around 0.7Vdc If tapping the AFM affects the idle, open the black cover on top of the AFM and see if anything is loose, or it might be that the spring for the barn door is on its way out.

Porsche-O-Phile

Are you running stock vacc. lines or purosil ones? If they're stock, check the little "Y" connectors for cracking/splitting. I had a very small tear in one (the one going from vacc. source to FPR & dampener) on my n/a and it made the car run so rough under load I thought it'd give me whiplash. These cars are VERY sensitive to vaccum leaks and even a little one will definitely cause poor operation.

snappy

I second the "touching the afm" if the afm voltage ot idle for that mater changes when you tap it then it is "bad" most of the time you can open it up and fix it. DO NOT CHANGE THE SPRING RATE. you can do some serious damage by leaning out the car. that said, you can adjust the arms to run on a new line just incase they worn out the line they were running in. which would cause the jumping when you tap it. let us know how it goes.

azmi951

Ok, to answer a few questions.
I have silicone vacuum hoses and there are no leaks.
I "borrowed" an AFM and FPR from a buddies car, hopefuly he will not mind. I will check on things Sunday when I have time.

To get the cover off of my AFM do I just carefuly pry the black plastic off?
Also I have the AFM voltage logging on my blitz boost controler and it is about .9v at idel and when it surges/misses it is all over the place (looks like a ricter scale, you know the earthquake monitor). Would that be the cause or effect of missing/surging?

fast951

Yes you pry the bloack cover off. When you put it back, make sure to seal it..
From the AFM voltage description, this is your problem.. If the AFM signal is way off (it sounds it is based on your description) the DME thinks there is more air going in and will add the fuel. The engine is getting much more fuel than needed and will bog, miss etc...
Try the borrowed components one at a time.. I think the AFM is the problem. If you can't fix it, you can get one for $100 or less. Many people upgraded to MAF..
Or you can just upgrade to a MAF

azmi951

Joh, trust me, the MAF upgrade has been through my mind. When I do it will be one of yours. I'm a college student so a MAF is a real luxury right now.

azmi951

Ok of all things it was the O2 sensor. I unplug it and the car runs right. I have a feeling the wires got burned and are shorting.

Who would have guessed that the O2 sensor would do that.