944 idle problem

[PCM944]

Hi everybody. I'm new here and this is my first post. I have an early 944 which has this problem. Sometimes when the engine is warm enough and the radiator fan turns on, the idle becomes very erratic. After shutting the engine down and letting it cool a bit, everything goes back to normal. And there are days that this problem does not happen at all. I appreciate any advise from you 944 experts! Thanks!

[SoCal Driver]

The fans do suck down a bit of current. Both have 25 amp fuses. I would start checking all of the grounds between the engine and the chassis and the chassis to the battery. This is part of the charging circuit as is the cluster of large red wires to the possitive terminal at the battery. Clean the battery terminals too.

If the battery is not new, four years old or older, then get it tested.

[PCM944]

My battery is new. I will go ahead and check the grounds and wires. Thanks SoCal Driver.

[UconnTim97]

Hey SoCal, my owners manual has one fan as a 25, and the other as a 16 amp fuse. Should I change them to both being 25 amp fuses?

PCM944, welcome to the board. As SoCal said, clean the grounds, my car ran so much better after I did that.

[SoCal Driver]

You are right. I think that the 16 amps is the actual draw for the A/C fan. The 25 amp is on the circuit with the balast resistor that runs the other fan when the key is off and the car is still hot. Must be to cover the load of the resistor and slow running motor. Don't change the size of the fuse.

Still 32 amps is quite a draw. I've seen my head lights dim when the fans come on.

[UconnTim97]

SoCal, there were 2 25 amp fuses when I bought the car, but one was burnt out due to the bad cooling fan. After I replaced the fan I put a 16 amp fuse in as it said in the manual. I thought the PO put in the 25 because it was blowing fuses.

OK, I will keep it the way it is...thanx

[PCM944]

FR Willk - The engine idles at 950 to 1000 rpm. But when the problem occurs, its very erratic, goes up and down maybe as low as 500.

[PCM944]

I haven't turned the a/c on since it's been cool lately. I'll try this when I get home later. However with the headlights on, it seems normal, but occasionaly will have the erratic idling when the radiator fan turns on.

[dangerous]

have you solved your problem yet? sounds like one I had with my 85 944 a few years back. Involved replacement of an O2 sensor for the fuel injection system. RSVP if you are still looking for answers.