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2 yrs ago I installed a k&N filter ( only ) in my 2007 EX coupe-with automatic trans.

recently I have had a stumble and low idle ( 500rpm) with the ac on that makes the car feel as if it will stall. at that speed it will stumble and then ramp up to 750 - a cycle which occurs about every 25-45 seconds when in DRIVE only.
the ac cuts out at that speed - the compressor turns too slowly??

Under driving, or in park or idle without ac - all is fine.
I checked several things and read that over oiling of a k&N can cause fouling of the air flow sensor.
Anybody have any idea if this is true or BS. I plan on getting a paper elemnt to test it out.

FYI- I checked all ground cables, changed plugs, cleaned the throttle body ( as best I could) and cleaned the air sensor. battery is 1 yr old. I also did the idle relearn. Things cleared up for about a week after , but now i am back to a intermittent stumble.

 
Rep Power: 234

Sounds like the compressor or compressor clutch is going bad.

 
Rep Power: 811

might also be the filter. they only have a 92% filtration rate when new, and around 96% when heavily used. oem spec calls for 99% for proper engine operation. the oil on the filter is also a problem and i've seen it clog almost every intake system sensor there is. im guessing your IAC and MAF are clogged. the IAC would explain the idle drop because if its clogged, it cant open to let more air in the engine when there is an extra load (like the a/c). i would take apart all the intake related parts and valves (that would be the throttle body, iac, maf, and any other parts you come across). clean the maf with a special maf sensor spray at the auto store. use full strength carb cleaner for all other parts. if you use carb cleaner on the maf you will destroy it. put everything back together after cleaning, drive around til the engine is fully warmed up, then park and reset the ecu (pull battery connection or FI ECU fuse). put it back and start the car, let it idle for 10 mins without using any accessories or pressing the gas. shut it off, wait 10 secs, then start it and go for a drive. hopefully problem solved.

 
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thanks I will keep you posted.

 
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I think you are right about the clutch.

I put a paper filter in and no change- so the K&N was not clogged.
I will clean the flow sensor again, but the R18 (and K20) in the 8th gen has electronic throttle- no IAC . The computer determines the idle speed.

I did notice that when the standard radiator fan kicks up to high speed, then I get the drop in idle as well. The AC fan is always on regardless of the clutch pulling in, as long as the AC switch is enabled.

I think I will pursue the AC issue first- need to take this to a pro.