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Discussion Starter #1
Just wondering if anyone has experienced this and might know the issue.

It's been 90-100* the past few days here and I have noticed when the A/C is running the motor feels like there is a huge load on it once it gets up to operating temp. Cold start the engine drives fine, but once it gets warmed up the throttle becomes really delayed in lower RPM's. I'll push the throttle down 75% in 1st gear from a stop but the car accelerates like I only gave it 10% throttle until about 2500 RPMs then the motor wakes up. Also if I don't rev it to 1500-2000 RPMs applying the clutch the motor will die from the load. I have feeling the compressor is causing all the issues because, If I turn the A/C off the engine responds just fine and has all it's power back.

Just wanted to see if I'm on the right track before I start buying new A/C components.
 

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I know my GT ran similar to that with the a/c on but it wasn't that severe. Even after I replaced the compressor when it went out there wasn't a noticeable difference.
 

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Your IAC valve may be the issue if its nearly dying at idle. When I replaced mine it took the dead spot out when coming on the throttle.

I’m almost positive it’s your IAC valve. Get a Motorcraft replacement. They are well worth the extra money.
 

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I live in Florida so I use my AC basically year round, and thats how mine feels as well. Even after the underdrive pullies the difference with the AC on/off feels like 30-40 HP.
 

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Due to all that heat what you are probably feeling is the computer pulling out all the timing to keep you car from detonating which takes all the power with it.
 

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Discussion Starter #6
Hmm... Ok... Is there anything I can do to help minimize this? Stop light after stop light, the car almost becomes undriveable. Every other car I have ever driven with A/C on you'll notice a slight drain on power but this is a whole different level.

Last summer I drained and filled the A/C system and beginning of this summer topped it off (So there shouldn't be extra strain from the system being low) and I also flushed cooling system and replaced the thermostat which made a huge difference in warm up and cooling performance.

Due to all that heat what you are probably feeling is the computer pulling out all the timing to keep you car from detonating which takes all the power with it.
I was also thinking something along those lines, but within a second of turning the A/C off the engine is perfectly fine. The car pulls hard again with zero throttle delay. Would the A/C affect the heat that much that quickly?
 

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I used to have a 98 p71, I had my ac tuned up and was kind of anal with the ac to be honest. You could definitely feel it when the ac was turned on but I wouldnt say it was as bad as what you describe. I also tweaked with the throttle stop screw to help with the high iac command values which probably helped so the iac didnt have to open as wide.

Enough babbling, to me it sounds like something with the compressor itself. Im sorry if Im going over something already said but have you datalogged?
 

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Discussion Starter #9
I actually replaced the IAC a couple years ago trying to fix some rough idling. Yes, I bought a Motorcraft IAC. That did help the idling but not the A/C load. Before I flushed and filled the A/C system last year I would never turn the A/C on because once the engine warmed up and the compressor kicked on it would almost kill the engine while idling. After the fluid change it idles so much better and I can't even tell the compressor kicks on anymore.

I do have a bluetooth ODDII unit I use in conjunction with my iPhone when I'm at the track, but I don't know if it has the ability to data log. What would I need to data log? I would have any idea how to read it either.
 

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Watch engine load, timing, and air intake temps with the AC on and off, if load is unusually high check the pulley on the compressor, if it pulls the timing or if the temp is really high its probably the tune
 

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Discussion Starter #12
I did. The IAC is maybe 2 years old, and the only issue the car has is when the A/C is on. Once the A/C is off the car drives like a champ. I've had this problem for a while, and the previous IAC didn't affect this at all.

I figured out how to data log with the app I have on my phone. I'll get a couple days of logging then I'll upload it to here and see what you all think.
 
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