CIS Idle & Power Loss

[Dial91177s]

The onging saga of my CIS problems.......backround here is that I've recently had the transmission reworked, thus the engine was removed from my '77 911S 2.7......now back in, I was told by my wrench that tests indicated faulty WUR & AuxAirValve.....I've replaced both and had him adjust the mixture/idle.

Here's where the problems start......idle continues to rev too high (2,500-2,700) and won't back off after warmup...indicating non functioning AuxAirValve....found that there is no ground to the unit, however power is being delivered. Could that be my issue right off the bat ??

If so, it may solve the idle problem...however the engine seem to loose all power at around 3,000 rpm......it's a bit inconsistent, however usually occurs in 4th or 5th gear and it's a rather violent jerk to the car when the tach drops down to Zero and then back up to 3,000 in about a split second. Basic power to the balance of the car is OK, just seems like the engine completely cuts off and then sparks back to life.

Help......can't seem to figure our what might be causing this to happen.....rather concerned that it's leading to a more serious problem in the CIS.....I've not yet checked out all the vacuum leak areas, however I suspect this may be a starting point......

[1bar]

I have a '77 930, which is slightly different. On mine, the WUR and Aux Air Valve are powered off the relay that powers the rear fuel pump. I had exactly the problem you describe, and it turned out the relay was bad, so the Aux Air Valve wasn't getting power to close it down after warmup.

I'm confident it's this valve. You have to trace the wires back, with your wiring diagram in hand, to find out where the problem is. It's probably really simple, like a wire broke where it's crimped to a connector pin, or something.

You need a DVM (Digital Volt Meter), and some very sharp needle-pointed probes (so you can poke through the insulation to test a wire when you can't reach the end of it). Also, you can get a kit that electricians use. It consists of a pulser unit, which you attach to a wire you need to trace, and a handheld wireless receiver. The receiver picks up a signal when it's probe is very close to the wire in question - making it easy to find a wire behind the dash out of a large bundle that comes from the engine compartment, for example.

You're on the right track.

Larry