Rough idling - 2002 Mustang GT

brianmef

Dirt-Old 20+Year Member
Nov 19, 2003
138
0
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Every time I turn on the defrost or AC my car feels like someone pulled a major vacuum hose off and the whole car vibrates like the timing is WAY off, and it loses a lot of power. This also happens when at a stop light and the cooling fan comes on. It goes away and runs normally if those things are not running. Does anyone have any idea what is causing this? Has anyone ever heard of this before?

Thanks
 
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I checked and no, the volt meter doesn't dip or anything when this happens. I can turn on the heater or anything else and it's ok. It's just when the AC or defroster runs, (both of which uses the AC compressor) or if the cooling fan comes on. After you turn off the AC or defroster, it takes about a minute or so, and then the car runs normally again. I'm taking it to Performance Ford here in Omaha Monday, so I hope they figure it out. I just thought I'd see if it might be something simple first that I might be able to fix. I'll let everyone know what it was after Monday if I don't figure it out by then. Please let me know if you have any more ideas. I wonder if it might be the IAC valve, PCV valve, or maybe the oxygen sensor?
 
I would disconnect the negative terminal and reset the computer. It might be a long shot but it may help or fix the problem and cost you nothing. My 02 has had a bouncing idle lately and after I disconnected the battery for a while and took my stock air silencer off it actually helped. Granted I think my car needs a good tune up, but might be worth a shot.
 
I would disconnect the negative terminal and reset the computer. It might be a long shot but it may help or fix the problem and cost you nothing. My 02 has had a bouncing idle lately and after I disconnected the battery for a while and took my stock air silencer off it actually helped. Granted I think my car needs a good tune up, but might be worth a shot.

Thanks. I'll try that.
 
CEL = check engine light

does your gauge cluster "sweep" when you start the car? thats a sign your battery is on its last leg.

sounds like a battery so far to me

The check engine light isn't coming on. During the coldest days this winter, the guages were sweeping. Probably due for a battery... :) I always thought that once the car is running, everything uses the current off of the alternator, because you can disconnect the battery cables and the car will still run. I could be incorrect with that though. Maybe if there is a sudden need for electrical power, the battery helps with that.
 
The check engine light isn't coming on. During the coldest days this winter, the guages were sweeping. Probably due for a battery... :) I always thought that once the car is running, everything uses the current off of the alternator, because you can disconnect the battery cables and the car will still run. I could be incorrect with that though. Maybe if there is a sudden need for electrical power, the battery helps with that.

i had my last stang towed to a shop because my car wouldnt start. i tried jumping it and everything.

well $200 later i had my battery replaced. the old was so bad even hooked to another car it wouldnt do anything. i was pissed cause i could have spent less than half that doing it myself.
 
The check engine light isn't coming on. During the coldest days this winter, the guages were sweeping. Probably due for a battery... :) I always thought that once the car is running, everything uses the current off of the alternator, because you can disconnect the battery cables and the car will still run. I could be incorrect with that though. Maybe if there is a sudden need for electrical power, the battery helps with that.

If you disconnect the battery while the car is running it will die. The alternator converts AC voltage to DC voltage. The battery output voltage is DC. This is why the alternator needs power from the battery. Older cars had generators instead of alternators. The generators output voltage was DC from the start. You can drive a car forever with a generator if the battery went dead. However, when you come to a stop you would have to keep the rpm's up so the car wouldn't die. This propably more than you wanted to know. I've had cars with generators and they work well. Alternators are able to keep up with the demand of all the electronics of the moderm cars much better than generators. Have the battery checked. Pearl02.
 
If you disconnect the battery while the car is running it will die. The alternator converts AC voltage to DC voltage. The battery output voltage is DC. This is why the alternator needs power from the battery. Older cars had generators instead of alternators. The generators output voltage was DC from the start. You can drive a car forever with a generator if the battery went dead. However, when you come to a stop you would have to keep the rpm's up so the car wouldn't die. This propably more than you wanted to know. I've had cars with generators and they work well. Alternators are able to keep up with the demand of all the electronics of the moderm cars much better than generators. Have the battery checked. Pearl02.

When I was in High School (a long time ago) I drove a '77 Ford Maverick (haha) and it had an alternator. Tomorrow I'm going to try that out and see what happens. I am also going to try the other posters suggestion to leave the cable unplugged for awhile to reset the computer. I would think the battery is good because it always starts the car without any problems. Thanks everyone for the suggestions and if you have any more before Monday, please let me know. Monday it's going into Ford to fix it if I don't before then.
 
bad/dirty IAC?

Also look at the IAC like Urban96 suggest. A clogged or particailly clogged EGR valve will cause Idle problems. I would think the EGR valve problem would throw a check engine light. You could pull both of these off and try to clean them. The IAC is easier to clean but the cleanings don't last long. The EGR valve itself is harder to clean. Good luck man. Pearl02.
 
Also look at the IAC like Urban96 suggest. A clogged or particailly clogged EGR valve will cause Idle problems. I would think the EGR valve problem would throw a check engine light. You could pull both of these off and try to clean them. The IAC is easier to clean but the cleanings don't last long. The EGR valve itself is harder to clean. Good luck man. Pearl02.

Thanks Pearl02 :)
 
One thing I love about StangNet is that if you need help, there is always someone willing to give advise. :)
I appreciate all of the advice I've received from every one of you. :nice:
 
If you disconnect the battery while the car is running it will die. The alternator converts AC voltage to DC voltage. The battery output voltage is DC. This is why the alternator needs power from the battery. Older cars had generators instead of alternators. The generators output voltage was DC from the start. You can drive a car forever with a generator if the battery went dead. However, when you come to a stop you would have to keep the rpm's up so the car wouldn't die. This propably more than you wanted to know. I've had cars with generators and they work well. Alternators are able to keep up with the demand of all the electronics of the moderm cars much better than generators. Have the battery checked. Pearl02.

Not true. My car died a few weeks ago while on the highway. Battery was drained so I assumed it was the alternator. Just to check I did the good ole method of unplugging the battery from the alternator while its running. If the alternator was dead the car would not run, well it did. It continued to run while the battery was unplugged, it was just rough. *WARNING*** DO NOT do this with newer cars!! It will run on just the alternator however it is dangerous to the electronics. The battery basically grounds the whole system, without the battery your alt volts and amps can go outside of the parameters and damage your cars computer or wires. It did end up being my alternator that was the prob, for some reason it was putting out amps but not volts, or vice versa can't remember. Point of the story, never unhook your battery on a running car.

Also Brian, it is your IAC they are peices of ****. I am having the same problems.