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larryb346 07-07-2013 09:13 PM

99 4 cyl surges at idle with AC on
My 99 idles great with AC off. Turn the ac on and sometimes the idle surges from 400 to 1500 RPM's. I can turn off the AC and shortly the idle returns to normal. This is a 4 cyl 5 speed. Any ideas? There are no code or pending codes showing

Big Sarge 07-08-2013 06:42 AM

Is the compressor engaging?

Double_a914 07-08-2013 08:41 AM

Its just the ac compressor engaging. Mine does similar but not as drastic as 400-1500. Its like 650-1150. Its where, when it engages for a few seconds, the extra resistance on the belt slows the idle. Once it cuts off the sudden loss of resistance frees it up and that's where the surge up comes from. Mines an 04 2.4l with 50k.

larryb346 07-09-2013 09:28 AM

thanks for the ideas.

The compressor is running and ac blowing cold. I think it is more than the compressor. It is a fast surge.
It's like your revving up and letting off and immediately revving it up again.
It's most noticeable after it warms up and has been driven a while with the ac on. You stop for a traffic light and it revves to 1300 to 1600 the drops back to 500 or so and then right back up. You can turn off the AC and it idles normally. It has to be something to do with the compressor load but I don't think the compressor would cycle that quickly. It doesn't do it until the engine is at operating temp and been there for a while. It takes 10 or 15 minutes of driving before it starts and not every time but at least 60% of the times I stop it does it.

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