Engine idle drops with A/C

[Yoni_d]

Ok, but in my case it should do its job correctly as long as this part is good and it seems to be good. or am I wrong?
its only an air valve..

[Danglerb]

Originally Posted by Yoni_d

I that case, what do you think? what things do I have to check and how? (beside making sure that the plumbing is ok)

I think that is basically it, if when that valve opens more air is added to the intake and sourced from below the throttle plate metered air, the engine will speed up.

Unless something else is going on at the same time, like the AC compressor engaging etc.

Once I get a chance to look over the wiring for your model I may have more comment, but haven't had the time yet.

[SharkSkin]

Originally Posted by Danglerb

The device in your last picture is the early style of idle stabilizer valve, and normally they are mounted behind the throttle body, all the hoses coming in going are new to me. Please take a couple more pictures showing where all of those hoses hook up, some close shots, but also a bit farther back to put them all in context.

This part is from a 944 -- probably flows about half as much air as the correct 928 part, which on a 78(or any 928 that has it) looks like the metal can pictured earlier in this thread. The correct part may very well solve the problem.

Originally Posted by Danglerb

CIS means early non electronic fuel injection. Your injectors open and close due to fuel pressure vs manifold vacuum, with the differential pressure controlling the rate of flow, and flow generally being "continuous while the motor is running".

Actually, the injectors open at a certain minimum fuel pressure, but flow rate is controlled by an air metering plate that moves a plunger inside the fuel distributor as the airflow changes. It is this plunger that controls fuel flow. They close below a certain pressure so that fuel will remain in the lines up to the injector after shutdown.