97 escort lx rpm's dropping and bouncing

[christopher1169]

I have a 97 ford escort lx and have replaced a dozen different things

a new head,timing belt,pcv valve,plugs,wires,alternator,iac valve,oxygen sensor and so on...but after getting the head replaced and the timing belt...it ran great for about 2 weeks...but then it started doing the same thing it was doing before it jumped time .....which is in while in park or while at a redlight in drive...the rpms will drop and then slowly bounce up and down a bit....Ive had it checked for vacuum leaks as i said gotten a new iac valve....but i noticed yesterday that hwen my electric fan cuts on it will stop doing it and idle fine...but when it cuts off after a minute it will start right back doing it.........Nothing shows up on the diagnostic which ive had done at a couple of shops...the only thing thats not new on my car or not like it wass is last year i got an a/c bypass pulley put on in place of the a/c compressor because the clutch went out in it.....but im stumped as to what it could be.....Someone please help...all help will be appreciated

[mightymoose_22]

I know you checked... but it sounds like a vacuum leak to me. Sometimes they are hard to find.