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My '05 MDX will idle rough or surge when at a stop or low speed and will sometimes do it at high speed if shifting gears like when I start to incline, etc. Now, I notice that it does not do this when I turn the AC off. I wonder if it's a bad AC compressor? I had one dealer tell me it was bad engine mounts and the compressor when engaged was jerking the engine and loose mounts. I had two other dealers look at it and they said the mounts were fine. Sometimes the AC will hiss quite a bit from under the dash on the passenger side when I do turn it on. I live in the desert so will need to address the AC issue anyways but wondering if anyone else can relate to this - engine jerking symptoms? PCV valve? other? Any insight is much appreciated!
 

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I hate to suggest a $300 option, but I think it might be your valves? (NOT PCV)

How many miles and when was the valve adjustment done last?
 

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I hate to suggest a $300 option, but I think it might be your valves? (NOT PCV)

How many miles and when was the valve adjustment done last?

Thanks - I did think of this but since the symptom isn't consistent when the A/C is off I'm not sure... 150K miles - don't know if valves have ever been adjusted. I bought it with 100K on it - so most likely never been done.
 

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A lot of shops will do a basic A/C diagnostic for little or no charge. About 5 minutes to check the pressures will tell you if there is a mechanical problem in most cases. You can also invest in a cheap set of gauges and do it yourself.

The vibration when the A/C cycles on is a very common complaint on older vehicles. It's mostly engine mount wear, and the front and right side mounts usually are shot by 100K. The rear mount is a major problem to replace because of it's location. If you can live with the vibration, it's not a big deal unless the front mount is actually broken completely. Front and side are easy DIY fixes.
 
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