old idle thread

[muzz]

I have a 1987 Porsche 944 with a 2.5 16v. When I first start it idles high, after a few seconds it idles rough at low rpms. It drives fine when hot but whenever I come to a stop it will either drastically drop in rpms and then shoot back up to 850 rpm or stalls.
I have check the temperature sensor and that is in ohms limit at all temperature ranges, I have battery voltage and 40 ohms at the auxiliary air regulator and the valve closes at start up, Idle air control valve works when a 12 volt is supplied.

I know its an old thread but can anyone help

 

[blease]

When my S2 did this, it turned out to be a perished hose to the idle control valve. It was cracked underneath where you could not see it.

 

[muzz]

I replace them hoses not so long ago, but I shell have a look.
Ta

 

[muzz]

My icv hoses seem ok, nice and tight.

I was wondering can the idle choke be increased??

 

[peanut]

I'd do a smoke test on the vacuum system . There are so many little inaccesible places for a small leak to screw your mixture on idle.
Also check the AFM resistive track around the low throttle position.
Also possible you have a leaky injector or possible faulty engine temperature sensor

 

[Paul 290T]

The ISV valves gum up over time, that will cause bad idle.

Also have you checked the throttle position switch is reliably sensing you've got a closed throttle, if not the DME will not know to start using the ISV

 

[muzz]

some things to do this weekend, i will get back to you.
many thanks