PJB

Lately my car has an erratic idle that jumps up and down a few 100 rpm. When it does the needle drops on the voltage gauge and the lights dim. When the idle isnt going up and down the gauge stays right where its supposed to be. I have a 130 amp alternator.

Also sometimes when coming to a stop the rpm drops to 500 and then goes back up to 800-900.

What could be the cause of these problems?

I sometimes get a check engine light and it comes on and goes off randomly. I scanned it awhile ago and it had a TPS code, something to do with low voltage. Would replacing the TPS fix all these problems?

I know..pull over...

My '89 5.0 LX (std) developed the exact same symptoms. I'd ask 10 knowledgable people for their thoughts on what the problem was and I would get 8 or 9 different suggestions. The only repeat sugestion was the MAF sensor (which I couldn't afford to replace at the time).

To this day I don't know exactly what the problem was but a change of spark plugs and wires took care of all the symptoms.

PJB

Ive got a different MAF sensor waiting to get put on but I need to get the adapter- its off a '94 5.0.
My plugs and wires are fairly new. The car runs fine except at idle.

AdderMk2

you dont need an adapter to hook in a 94-95 maf... the "adapter" that is needed is just to hook on an air filter.... plug it in and see what it does.

Does the car idle weird when cold, warm, both... etc

If your car idles rough when warm, unplug the IAC valve. If the erratic idle stops, you know your IAC is bad. If it continues, suspect a vac leak!

PJB

The car idles weird when its warm or cold.
The previous owner mentioned something about the IAC sticking or something like that but I dont really think he knew what he was talking about. He gave me some kind of idle adjustment plate thing to manually set the idle but Im not sure what to do with it. I dont think he knew either.
I know the adapter is for the air filter/intake because of the shape. I suppose plugging the new one in wont hurt.

Is there a way to check for a vacuum leak? Ive got some kind of vacuum tester but Ive got no idea what its for. Its like a pump/gun type thing.

Blckstng93

Check the rubber hoses under the front of the intake for any holes or tears. I just fixed an idle problem on my 93. It idled rough warm and cold and only during idle. The hose leading to my purge valve had a hole in it right at the metal fitting at the intake.

Listen closely for any 'hissing'.

Keeping the IAC clean is always a good idea tho. Just take it easy with the gasket and youll be able to reuse it. If your TB is black inside, clean that while youre in the area. Preventive maintennance.

kev2369

I'm agree with the vacuum suggestion. These intakes hide some vacuum hoses that can crack easily and suck air. But another problem could be that your idle air control sensor could use a good cleaning. I'd pull in off and take a little carb cleaner and spray it out good and go from there. Really look for vacuum though, cuz that is what solely determines how your car idles. And if all else fails, reach down there on the throttle spring and adjust that screw in a little with an 8mm wrench so that it won't allow it to drop all the way down. Good luck

PJB

Thanks guys. Ill definately have to clean the IAC and check the vacuum hoses on my day off.

2 kwik

I would pull the throttle body off and clean it as well as the iac and egr valve as they get all carbon'd up

kev2369

That's not a bad idea either... Just a few more bolts and you've already got the good ole carb cleaner out... Good luck