5.0 revs at idle

[steven]

Looking for advice on mustang motor in Ranger. Have been trying to get it to run correctly for awhile with no luck, When I start it up it will idle up then drop down to 800 ish rpm and run for about a minute just fine then it revs up on it's own to about 1500 and stays there for about min or so then drops back down to 800 and then back up to 1500 and repeats.
Adjusted timing to 10-12 and seems to back fire through throttle body little, can turn it back past zero and seems to run better. This is all being down with spout unplugged and IAC unplugged. Have put at TDC on number 1 and balancer is on 0, TPS is around .9 volts. Running a Ron Francis harnis, changed water temp, and air temp sensors. Motor is out of 91 mustang, AOD, Explorer P heads, intake and throttle body, very mild comp cam, and headers. Any help would be much apricated.

 

[ericbphoto]

I'm no expert. My gut feeling is that it should idle around 800, maybe even 700. Have you checked for vacuum leaks? Almost sou ds like it's going in and out of closed loop operation. I would suspect something with coolant temperature. Is the thermostat good?

 

[steven]

I have triple checked for vacuum leaks, and have replaced temp sensor and also ohmed it out and seems like it is good.

 

[scotts90ranger]

what about the oxygen sensor?