notaguru

This 4.7L US '83 has 68k miles and in general runs fine. However, it tends to idle low, intermittently dropping to zero on the gauge and bumbling along.

Search produced a treasure trove of information on the later engines, but little on this one. Where is that widget, what does it look like, and assuming it's faulty what can be done about it?

Thanks!

Ducman82

4.7 should be a euro engine. the AC idle kick up is located on the engine brace.

notaguru

Found it - maybe.

I looked online for images (4.7L idle air) and got a part number 0280140227, which is applicable to the '83 and the '84 ONLY (apparently).

On my California-spec car built Apr '83, the idle air stabilizer/controller is a Bosch part located on the passenger side of the engine, inaccessibly under the intake system.

GregBBRD

There is no stabilizer until 1985.

What you are looking at is actually part of the cold running compensation system. That valve allows more air when the engine is cold and is responsible for high cold idle. Once the engine warms up, that piece is completely closed.

Of course. If that piece sticks or is not functional, the above does not apply.

notaguru

Thanks! I knew there would be guru help out there...

Most ECU-fitted cars have a closed-loop idle management system. Is there something like that in my 1983 4.7? If not, what did Porsche use to control idle speed across the temp band?

notaguru

At least one early 928 (my '83) appears to have open loop idle.

There's a large screw in front of the spider, which works against a spring. It's accessible with a common slotted screwdriver. That screw evidently adjusts idle air, and when the ECU learns the O2 level (from the O2 sensor), it adjusts fuel accordingly. So idle air can be adjusted manually, and the car responds. Well, mine did.

I think. And if I'm right, then Porsche missed a revenue opportunity by not requiring another special tool...