Surging idle in park?

MrStang123

New Member
Jul 6, 2004
65
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NY
Ok well my gf's idle in her 95 gt was acting kind of funny. It was hoping around in between 1000 and 1500 Rpms. But it was only doing this in park. Not in any other gear. Her mechanic had said that she needed a new idler pulley when she had first bought the car. Could it be the pulley going? Or perhaps fuel injector cleaner she had put in the other day?(Althought after it was put in no such funky idling happened). I had searched for this topic but found nothing about doing this just in park.
 
Does it do this when the motor is hot or cold (or both)? Is it fine once in drive or neutral?
Any codes?
More info please.

Good luck.