Idle with AC issue - TCCoA Forums
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post #1 of 3 (permalink) Old 10-31-2013, 08:23 AM Thread Starter
Join Date: Mar 2006
Location: EGV, IL
Posts: 18
Idle with AC issue

Good day everyone,

So apparently I have something going bad in my engine, as in hopefully a sensor, that affects my idle and the AC.

To start, 96 Tbird with a split-port (03 Mustang 3.8L donation). Runs quite smooth normally. When I have the car in Park or Neutral and turn the air on, it will only briefly cycle the AC clutch (less than two seconds) and leave it off. While doing this, it will decrease the idle speed from the approx 750rpm to about 500rpm or a little less. Of course it goes back up after the clutch makes its cycle. The AC works fine in gear, and this problem had just started maybe two weeks ago now. I just had the idle going crazy on me along with a TPS trouble code, which seems to have been resolved by cleaning the MAF and IAC. I also took off the TPS to make sure that there wasn't a dead spot in it, as in ohm reading through the range increasing for more throttle.

I have also messed around and noticed that if I accelerate the engine to >1500rpm, it will cycle on the AC and drop the rpm to a bit under 1000rpm, but will still go under 500 if I let off the accelerator

I have been trying to look here for a solution, but I haven't really had much luck. The common explanation is that the ECM will readjust for the AC kicking on. That is fine, but I would like to know where the ECM gets its information as to the AC being turned on inside of the car. Obviously, it isn't being communicated well somewhere in the line. I've heard a sensor in the compressor of some cars will tell the ECM to increase rpm for a larger load demand for the AC, but how does it work in the tbird?

wakko_99 is offline  
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post #2 of 3 (permalink) Old 10-31-2013, 08:56 AM
Kind of slapped together
Join Date: Jan 2010
Location: Bossier City, LA
Age: 63
Posts: 4,851
According to the EVTM, the Pink/LightBlue wire from the clutch high pressure cutout switch through a junction block to the ECM.

OTOH, this is easier explained by the IAC not working. I'd be checking and/or replacing that first.

Did this start when you cleaned the IAC? Did it start during the split port swap? Or is it totally unrelated to either?

BTW - Not to sound like a broken record, but you DO need the EVTM for this car to troubleshoot.

RalphP is offline  
post #3 of 3 (permalink) Old 10-31-2013, 12:24 PM Thread Starter
Join Date: Mar 2006
Location: EGV, IL
Posts: 18
Thanks RalphP for the reply.

No, I do not have the EVTM for the car. It would help immensely in dealing with this problem and others that I have run across. I don't believe that it is related to the swap, since the AC had run without issue for the summer until about two weeks ago and the swap was a bit more than a year ago. I did have some things replaced in the AC system, no new compressor, and that was in the beginning of the summer as well. The issue came up independent of cleaning the IAC, and improved a bit when I cleaned the MAF sensor.
wakko_99 is offline  

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