Porsche Repair: Porsche rpms, air filter assembly, k jetronic

Question
Gentlemen,I have a 72 911T,bone stock and just rebuilt.After my winter storage we have had a problem I can't seem to figure out.The motor ran great after rebuild but now is getting hung up in the midrange rpm's.The motor starts up great. the idle is fine,if you depress the pedal the rev's can get hung up around mid-range and won't come back down.Start the car,let it warm up,hit the pedal, rpm's climb,let off they won't come back down.Even if you burp the the motor quickly it will still get hung up.I have been all through the cable and linkage system,all works freely with no resistance.It's not happening because of the cable or linkage. The motor itself? How about air pressure? Can we be creating a vacuum? something within the motor is not allowing the rpm's to come down. The mechcanical injection is still on the car and has been gone through at the time I had the rebuild. Could we be dealing with air and hoses? If you believe I'm on track please be specific as to what to look for in the engine area. I didn't do the rebuild but I can find my way around the car with some level of mechcanical ability after 33 yrs of ownership. Loading up the 911 for a 4 hour ride to the shop seems to be a bit too much. Can you HELP?  

Answer
Hi Terry,

Based on what you've said it can't be...and the symptoms you report...I suspect there's only one of two answers.  I realize you said the fuel injection was gone though but here's the problem:

The K-jetronic fuel injection system has a "plate" covering the inlet of the airflow meter.  This would be between the air filter assembly and the intake manifold.  The plate sits in a cylindrical but short tower (the shape at the top reminds me of a nuclear power plant tower).  At rest, the plate sits down in the cylinder preventing crud from entering.  When the engine is running the plate moves up and down in relation to the air being sucked into the engine.

I won't go into all the why's of that, but if the plate cannot move freely when the air pressure drops off, then the mechanical injection will keep pumping fuel to match what it thinks is coming in.  This is because the injectors are basically calibrated to follow the lead of that plate.

If the plate is not sticking, then you've got to dig even deeper.  I can't tell you what it looks like exactly but what you'll be looking for is the throttle "butterfly".  Very simlar to what's on the two and four barrel carbs on US cars, the butterfly opens and closes in response to gas pedal input.  It is located just past the air flow meter and adjacent to the intake manifold.  Now, you said it's not a cable issue and this surely would appear as exactly that.  So...I believe it's got to be the air plate.

Dave