Q: Q: Engine idle fluctuates

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When traveling above 20MPH, if I use the breaks and take the load off the engine (press clutch/shift to neutral) the engine RPM drops instantly to 1,000 and bounces between that and 1,500 until either my speed falls below 20MPH, or I let off the break pedal. My engine has a high idle problem I'm also working to diagnose and the two may be related. Normally with no load on the engine it idles at around 2K. Sometimes this can be adjusted by revving, which drops it by 500-1K. The idle fluctuation when breaking problem is somewhat intermittent. I have an after market K&N filter on it. I've cleaned the MAF and throttle body. Replaced the idle air control valve. Changed spark plugs.

My car has 175000 miles.
My car has a manual transmission.

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