JR Reed

I am still chasing Idle problems. I am wondering what the Aux. Air Valve (AAV) does. if bad, Will it cause a bad idle only when the engine is cold or any time. What are symptoms of a bad valve and how do I replace the thing?

Thanks!

SoCal Driver

Depends on where the valve sticks. The early 944's use a bi-metalic heated spring to close the valve. The valve is a sliding door or knife valve like you see on RV holding tanks. The slots or guides of the valve blade get gummed up with engine oil residue.

Taking it off and giving it alternate blasts of carb cleaner and wd-40 can restore it to almost new operating condidtion. You can reach in the ports and move the valve/gate/blade with a sharp pointed scribe or awl.

The valve lets air bypass the throttle at cold start and thus increase the idle. As the bi-metalic spring heats up from the 12 volts the fuel pump relay sends to it the blade closes off and reduces the idle.

So the valve usually sticks open -- high idle.

Note: Post 85.1 cars use a different system to control the idle. The DME actually drives a tapered seat valve closed or open depending on the temp sender and the speed sensor.

JR Reed

Great Thanks for the help. Any advice on how to remove the thing, I think i is under the intake manifold. Canit be removed without taking that manifold off? I do have a high idle (1200 rpm) after the car warms up. While it is cold the idle fluxs between 500 and 1000. There are times it just runs poorly even after warm.

Thanks

SoCal Driver

I would take off the intake manifold with the intentions of fixing any vacuum leaks. Including the larger vacuum hoses to the valve and other locations like the brake booster.

Get a set of reseal kits for the injectors too.