[BottleNose]

This "Throttle Valve Control Pressure Regulator" device, located between the throttle body and the sensor plate, really killed the idle when I sprayed carb cleaner directly at it:



>Description:
>"Early CIS only ('73 - '75) Operated by a cam driven off >the throttle shaft. Enriches the mixture at full throttle and >at idle by decreasing the control pressure.

>Failure mode: Leaking diaphragm keeps fuel mixture too >rich at part throttle"

Can these have vacuum leaks or is this a sign that this unit is faulty? How do you test and troubleshoot this part?

My '73.5 911T CIS starts and idles fine, but stumbles and backfires whenever you try to accelerate. If you hold the throttle steady at higher RPMs it will be smooth, and decel is OK, but any acceleration causes severe bucking and backfires.

So I read here that the first thing to do was to check for vacuum leaks by spraying carburetor cleaner around the engine and seeing if the idle increases (indicating a vacuum leak.

I sprayed at all the possible vacuum leak areas, and nothing affected the idle except spraying under the CIS intake boot (the big one on top of the fuel distributor and airbox). When sprayed under there it LOWERED the idle and the car almost stalls. From there I determined the above device caused this.

Thanks for any advice.