'94 Mustang: Rough Idling on Start

[Ereinion]

Hi folks,
I don't know much about cars but I'm trying to learn. My good old '94 Stang has been such a faithful little car, and I love driving her.

Car:
1994 Ford Mustang (base)
V6, manual transmission
mileage: unknown (estimated > 250k)

Lately though, she's had a lot of trouble when I first start her up. It seems to be worse on cold days (below 40F), although it's not limited to that either. It seems to be more related to the cold season than the current temperature when I start her.

Anyway, when I first start her she turns over and starts without a problem, then idles very roughly for 10-15 seconds. She struggles to stay running, rattles and vibrates a lot, and nearly stalls out several times. It doesn't seem to make any difference whether I engage the clutch or not. Then, after several seconds, she'll rev the engine really high and the tachometer shoots up. Usually this calms down after several seconds and she runs fine, but sometimes she'll keep running at high RPM for a while, making it difficult to drive (sometimes I have to partially engage the clutch to keep the speed down).

I don't know if this is normal for a car of her age, in the winter, or if there's something else going on? Any tips?

 

[97JF]

Try replacing or cleaning out the Idle Air Control valve , had a similar issue recently with mine , cold starts it wouldn’t idle for about 15 seconds and would shut off unless I was on the throttle

Cleaned out the IAC and it’s fine now,
If it happened again I’ll replace the IAC

 

[ttocs]

the fact it is firing right up would make me think its not fuel related but just because its easy lets test the pressure. Next time its cold turn the key to the on position(not start) and listen for the fuel pump to prime for 5-6 secs and then turn the key off. 2nd time start the car and see if pressurizing the system a little more helped and if it runs better.

 

[Flade]

I agree starting with the IAC. The computer uses the IAC to control the idle. it opens and closes to let air in. When it is sticking or not working correctly the engine will idle badly. If you replace, be sure to get a Motorcraft part. I have had bad luck with other brands.

When was the last time it was tuned up. I.e. new plugs, air filter, fuel filter, ignition wires, ignition coil. These have to be replaced periodically.

Do you ever use a fuel injector cleaner?

Have you ever cleaned the MAF? If it is dirty the computer will miscalculate the amount of air coming in, and use the incorrect amount of fuel.

have you checked for vacuum leaks? The most common issue is the vacuum tree, near the drives hood hinge. The first system is usually the heater/ac will only come out the floor or defrost vent.