Engine idle question 02 gt auto

Hello,

I have an 02 gt automatic vert. with 35000 miles.

The question I have is I have noticed here recently that it seems to be idling a little rough in drive while stopped. It is noticeable on the tach as I can see it move about 1/8 of an inch or so up and down around the 500 rpm mark. It is also noticeable in the brake pedal as I can feel it in my foot while at a stop. It seems to run fine other wise and there is no sign of stalling. I run this car on 87 octane and fill it up with 93 octane every third tank or so.

This only happens when the a/c is off. if I turn the a/c on it seems to stop as I think this changes the idle setting, (Not sure). I have had the fuel injectors cleaned and had the car at Ford for service here a few weeks back for an
un- related oil leak problem and they said they found no codes or problems when I complained about this to them.

I just don't ever remember it doing this before. So am I being paranoid, (car is almost out of warranty) or is there a problem here. If so any suggestions?

Thanks in advance.............. David

Problem fixed. Got some spray cleaner and cleaned out the intake. Works great now. Real smooth idle.