i have an 06 4.6 v8 that just recently started to have some problems idleing while the a/c is on. it has about 82,000 miles on it and i just replaced the plugs about two weeks ago. it only does it when the a/c compressor turns on and off, it will drop to about 400rpm's then jump to about 1100rpm's. can anyone tell me what might be causing it to do this.