1991 928 stalling and idling funny

[eyal928]

I bought a beautiful black 928 s4 in black with black interior, it is in superior condition. However, I am having this idling problem. I will drive the and when it starts to warm up the check engine light comes on and it starts idling funny, revving all the way up to 3000 and then back down and up and down. Sometimes it will stall altogether. I got the check engine light evaluated at Porsche and it comes in as code 14- engine coolant. I replaced the temp sensor and the air flow meter, it started working better. Then my mechanic told me he changed some hoses that were leaking and it started all over again. The idling goes up and down and eventually it stalls. Any suggestions? We believe that the air flow meter is no good so I sent it out to be rebuilt, hoping that is the problem. Some assistance please to get this bad boy back on the road where it belongs

[Landseer]

Where are you located?

[eyal928]

Long Island, New York

[Landseer]

A little far from me in VA.

Idle control valves, like the hoses and vac lines beneath that intake have a finite life.
Sometimes a shot of WD 40 into the inlet hose can free it.

Stuck idle control valve, also, bad or misadjusted throttle position sensor can cause surge.

Rebuilt MAF is a good idea, too.

Just based on your description of bad vac hose, I'd think you'd want to consider an intake refresh. My experience is that the problems are layered. Some of these cars even have the ticking time bomb of original fuel hoses, so that can be remedied during an intake refresh.

Check rennlist 928 forum on your 91 because there are a higher incidence of later model 928 enthusiasts and deeper, searchable archives that could help.

[eyal928]

Thanks for the info, I really appreciate it. The car is a beauty but I am battling to get it right, I also had the torque tube replaced when I first bought it. I will check rennlist too.