Finally made some progress! Sort Of ! Also I have Question at the end!

[metr0p0lis1927]

After three weekends of attempting to repair a leaking fuel return line I finally got it stopped and while working on that I found a shoddily patched place in the other fuel line going to the engine and replaced that (I thought it'd be a good idea to use ACTUAL injection hose and some clamps too!) and when I went to the top of the tank to hook up the new return line I found a broken wire to the sending unit and repaired that as well... all of which put me back at square one. Not Progress you say? oh you are mistaken because at square one I am now able to start actually determining the cause of my BIG problem which is that the car runs fine to 1800 rpm then lays down and tries to die, obvious fuel delivery problem you say? No kidding says I, so since I now know that the car not only has fuel in it and that fuel is definitely going where it needs to be, I begin to look at the AFM/ Barn Door again. So since I know the Darned thing opens my Dad and begin to question how well it opens but the air box is installed right now and its 1 AM so I don't really want to take it off (been under her for 8+ hours I was tired) so I pull the top off and pull the filter and stick a mirror back there and shine a flash light so I can see down the throat. Dad starts the car and runs up the throttle and sure enough at 1800 rpm that door stops opening so in a moment of exhaustion driven clarity I walk to the rear of the car and pick up a leftover piece of hose go back to the front and tell dad to run it up again but this time when it hit 1800 I shoved a hose down through the door and guess what the car didn't die!! nowt only did it NOT die it took throttle normally all the way to 3000 rpm when dad let off and opened the window wanting to know what the heck I did (he couldn't see me) to which my response was "SHHH! Turn the car off! See if she'll start!" She did and this time he ran her up to 4000 and held it , then he came off the throttle suddenly and once again the car didn't die it just went back to idle , on the throttle again , this time to 5000+ and held it for a minute or so and right back to idle! So as of 2 AM this morning, my car, for the first time since I've had her, and for who knows how many years before, went for a drive of more than 150 feet, in drive not reverse, without out flooding, or laying down and never died! and the engine even reached operating temperature! She went up and down our mountain a couple of times! We actually put a couple of miles on the odometer! That my friends is progress as far as I'm concerned!

Now for the Question !
Does the fact that can only get normal behavior from the car if I run a hose down the AFM to keep the door open, indicate that my AFM is broken? or would there possibly be a factor keeping the door from opening completely? Vacuum issue maybe?

[jstobo]

I'm sorry but I do not understand your "barn door" terminology. Are you talking about the throttle plate in the throttle housing? If so, the throttle plate is mechanically opened by the throttle cable. This allows more air to pass which the AFM measures(if working) and the computer adds fuel through the injection timing. The AFM is simply a hot wire. If the throttle plate is not opening check your cables. To check the AFM, you can measure the resistance of the AFM pins and finally check to see if you get a voltage change at the AFM when you blow air over it. The LH computer has a limp home mode when the AFM fails. It has one fuel ratio setting at less than 2000 RPM and one at >2000RPM. The car runs but very rich. If the car is idling with a lot of black smoke then your AFM probably needs rebuilding. I hope this gives you some ideas.

[jstobo]

I suddenly realized that you probably have a L-jetronic system in which the air is measured by a flapper before the throttle plate. The is called an AFC system and AFM is more commonly used for the hot wire sensor. I am sorry if I misunderstood. Below is a troubleshooting guide for the AFC system.

[metr0p0lis1927]

The Barn door is referring to the door in the AFM which should open more as you add throttle the door is attached to an big coiled piece of metal which gives it tension (similar to being spring loaded) as the door opens further an arm attached to the center of the coil moves along a plate on a sensor/circuit board that has several set points on it , as the arm passes over these set points it relays that to the computer which then adds fuel based on the amount of incoming air, mine has 6-8 set points on it not 2 and limp home is 1500 rpm. My afm is in no way mechanically connected to the car, it has a big O-ring that sets down in the lower end of the throttle body, the wire that plugs into the sensor plate , then the breather housing bolts directly to the AFM. the throttle plate you're talking about is in the the throttle body housing. The door I'm talking about is probably 4-6 inches before the throttle body , its the first door the air goes through from the intake at the bottom of the air cleaner assembly. if i don't have the hose shoved down in it the car idles fine and isn't running rich and the door works fine but at 1800 rpm the door wont open any further hence the computer doesnt add ant more fuel so the throttle doesn't respond. With the hose in it the the door is open all the way and the throttle response is normal (or at least greatly improved) but at idle it does run rich (door wide open=fuel being added for wide open throttle ) so I understand the richness at idle, that isn't my problem since I don't plan to drive the car with a random hose shoved down the air intake that doesn't belong there. The AFM on my car which is an 84 is, I believe, different from the one on your 85 in that mine isn't just a hot wire, its an entire apparatus which apparently functions entirely off vacuum provided by throttle body, not through vacuum lines .

[metr0p0lis1927]

Jstobo : Yes though I'd only ever heard it referred to as an AFM and its listed in the porsche parts lists as an Air Flow Meter so that what I called it. And thank you for the troubleshooting guide I have one that's remarkably similar to that which is what pointed me to the AIR flow Meter to begin with. i was calling it a barn door because thats what the 944 guys call it and I was able to find tons of info about it on some of their websites and the moniker stuck in my head after several hours of read about them.

[tmpusfugit]

The barn door is pulled open by the flow of air from the air filter through it and to the throttle body. If the "o" ring seal is not good it will give you symptoms like you are seeing. There is a check out proceedure and a repair thread for the sensor...how to reposition the sweeper that reads the resistance and reports it to the computer, which in turn tells it how to behave. I would suspect first the seal or more often just how the seal is working or not working when the AFC is in position. I have not seated mine properly more than once, and one of my fellow local 928's fought a leak in the seal for a very long time before he found it...hard to troubleshoot, easy to figure out once you have seen it and worked with the symptoms...