Just to see what happens I replaced my idle air control valve (IAC) with one from a 1996 302 truck (I'm planning to use the IAC with a intake/MAF project later - see here ). I didn't reset the computer as I thought the IACs should be similar enough. What happened was a high idle at around 1700 rpm dropping down to about 1200 rpm in a step-like fashion. When it reached 1200 rpm the engine stumbled very briefly, the computer adjusted the rpms back to 1700 rpm and the game started anew. What's so different between the IACs from 88 and 96?
What's going on? Will I be able to use the IAC from the 96 with my A9L Mustang computer?

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1988 F-150, V8, 5.0L (302cid), 5spd, SuperCab. Shorty headers, K&N fipk, MSD 6a ignition, Accel 300 8.8mm race wires, Accel supercoil, Accel rotor cap, Bosch 4 Platinum plugs, RanchHand bumper, Summit block protector, Cloyes true roller timing chain, electric fan, Fumoto valve.
http://brembs.net/cars/FordPU.html

 

While very similar, some have different size and different length valves. However, the problem here was that you didn't reset the ECM. That MUST be done. It will probably run fine after that.

Take care,
-Chris