rough idle when cool a/c on - TCCoA Forums
 
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post #1 of 4 (permalink) Old 10-30-2006, 09:04 AM Thread Starter
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rough idle when cool a/c on

this started a while back and is getting worse.
If the shut the is car off on a warm day, the a/c selector is left in the max postion full cold (turn to the left). Most times on start up the car runs rough like a cyclinder missing, or a bad plug/wire. until the temp guage climbs up into the normal range, when stopped at a light with car in drive and foot on the brake the whole car buzzes and vibrates.
Well i took the car out yesterday (usually my son drives the cat) and this phenoma happened, he said "see day thats what i'm talking about". I reached over and shut the air off. the car settled down smooth as silk, the idles was rock steady at 550 rpm , the perfromance from a standstill was impressive. After a few minutes i turned the air back on no problem. latter in the day i repeated the sequence, had the same problem when cool, till i turned the a/c off. 5 minutes later turned the a/c back on and no problem.
So what in the start up/cold engine scenario is so adversvley affected by the a/c compressor? Is there a sensor malfuntion? A/c works fine, the pressures are in range both sides. new plugs and wires within the past year.

any thoughts ?

i'd rather go slow than not go at all

1996 MKVIII air ride delete
2007 Royal star venture (loaded)
2007 Ford free style 3.0 v-6
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post #2 of 4 (permalink) Old 11-02-2006, 09:11 AM Thread Starter
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bump,
first time i didn't get a reply.
picking myself of the floor.

i'd rather go slow than not go at all

1996 MKVIII air ride delete
2007 Royal star venture (loaded)
2007 Ford free style 3.0 v-6
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post #3 of 4 (permalink) Old 11-02-2006, 11:35 AM
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Maybe the IAC is sticking when it's cool and is not upping the idle properly when the A/C is engaged and the load on the motor is increased, thus bringing the idle down to the point where it wants to make the motor stumble. Then once it's warm it moves freely and is not an issue.

Also, maybe clean the MAF?

Jay

These are highly engineered precision vehicles, the first step in diagnosing the problem is to strike the suspected offending part sharply and repeatedly with a blunt object, then re-test.
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post #4 of 4 (permalink) Old 11-03-2006, 10:51 PM
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I have this same problem (95 Mark VIII), only now the car will vibrate when the A/C clutch is enganged any time, whether the car is warm or cold. I tried cleaning the the MAF, it did nothing, as it was already clean.

My idle RPM's do not seem to increase at all when the A/C engages, i'm curious how much, if any, does everyone elses RPM's increase when the A/C engages? The vibrations only happens when the car is in drive and the car is stopped, when the car is in park, RPM's increase from about 550 to about 700 and stop the vibrations.
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