Car dies after driving with a/c on??? - Mustang Evolution

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Old 06-19-2005, 05:41 PM   #1
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Car dies after driving with a/c on???

Hey guys, I have a very weird problem and I need some help.

First off, let me say that my car is completely stock except for some 2 chamber flows, I don't even have a k&n filter...

Anyways, here's the problem:

It's just starting to get warm enough for a/c here in cali. So I drive around with the a/c on for 10-15 min. to wherever i'm going. I get there, turn the car off, do my thing, then come back out to start the car. It will start fine, and idle normal for a second (~750 rpms) then the idle will jump up to ~1300 rpm then it will start to act crazy and drop down to ~400 rpm then back up then it will completely die. I can start it right back up after it dies, and it will do the exact same thing. I sat in the Best Buy parking lot yesterday for 20 min. doing this. Starting it, let the idle go crazy, die, and repeat.

I've only noticed it does this when i've driven with the a/c on, or if I have the radio, headlights on and i'm turning the steering wheel. Anybody have any suggestions? I just cleaned out the MAF on friday and I ran some Seafoam through it, but I had this problem before and after that...

HELP!!!
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Old 06-19-2005, 05:47 PM   #2
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Oh, I forgot to add, I have to drive the car a good 5 minutes keeping the rev's up (above idle) to get it to normal itself out.
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Old 06-19-2005, 05:53 PM   #3
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check your belt and all your pullies.
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Old 06-19-2005, 06:01 PM   #4
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Mine did the same thing after I put in the new motor. Of course, my situation may be a little different b/c my car is not quite stock. The accessories are putting a load on the motor and causing the idle to drop and the loss of power is not being compensated for by the EEC like it should. What I had to end up doing to mine is raising the base idle. It was set at about 750-800 rpms and I had the exact same symptoms your having. Now, I raised it to about 900-950 and it does just fine.

However, that may not be necessary. First I would clean your IAC (cylinder shaped sensor on the front of the throttle body). To clean it simply take it off and spray it out with some carb cleaner. You also may want to check your TPS sensor and make sure it's in range. Another thing that could cause it is the 10-pin "salt and pepper shaker" connections being dirty. Basically all the common fixes for 5.0 idle problems may help.
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Old 06-19-2005, 06:36 PM   #5
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ok, I checked the belt and pullies, everything looks fine. I did notice however that the pump underneath the alternator (smog pump i think???) wasn't even connected. The hose that connects to it was just hanging in space. So I fixed that. I also saw (while i was under there) that big power wire (i think it goes to the starter? it runs across the oil pan...) was rubbing against the harmonic dampener thingy and the wire was starting to get chewed up. I fixed that too while I was down there and moved it a little so its not right up against the dampener.

I'll definately clean that IAC, but how do I check the TPS? And I assume I can just do a search for these "common 5.0 idle problems"?

Sorry if these are stupid questions, i'm kinda a n00b...
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Old 06-19-2005, 09:59 PM   #6
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I am not positive, but I think you check the TPS with a voltmeter and it is supposed to read in a certain voltrange, but as I said, not positive, and don't know that range.
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Old 06-19-2005, 10:10 PM   #7
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The smog pump being disconnected shouldn't affect anything. You can actually remove the pump and run a shorter belt for a couple extra horsepower.

To check the TPS, you'll need a digital voltmeter. The TPS is a small black sensor that sits on top of the throttle body. It will be held in with two screws and have a wiring harness plugged in it with three wires, one green, one black and the other I can't remember off hand but isn't really important. You'll need to pierce the green and black wires with pins so you can touch the positive wire of the voltmeter to the pin in the green wire and the negative wire of the voltmeter to the pin in the black wire. To test the TPS, you need to have the key in the ignition turned all the way forward, but the car not cranked (this is called KOEO, Key On Engine Off).

The voltmeter should read between .92 and .99 volts. If it is barely off you can try "adjusting" the TPS. The TPS is not actually meant to be adjusted, but by loosening the screws holding the TPS in you can rotate the TPS on the throttle body and change the reading. When you get it within range, tighten the screws back on. Some people will even go as far as filing out the screw holes to allow for more adjustment, but if this is necessary I would recommend buying a new TPS.

As far as the other "common problems", just try googling "5.0 idle problems" and you should come up with more information on the subject than you'll ever want...
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Old 06-20-2005, 12:36 AM   #8
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Another thing you may want to check is your coolant level and watch your temp guage to make sure your car doesn't get a little extra warm when you run that A/C. Could just be a coolant level problem, could need a thermostat.
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Old 06-21-2005, 08:10 PM   #9
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Thanks for the info guys, I'll start checking all these things, hopefully I'll get it figured out....
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