I recently traded a broken guitar for an 89 Bronco 2 XLT 4X4 with a cracked head, blown heater core and broken automatic door locks (except the hatch still locks) I dropped around $500 into it, used head, new head gaskets and intake gaskets. Engine inside was nice n clean. I'm 3rd owner, first owner took awsome care, changed oil regularly. 2nd owner ran it without much care. installed new heater core and then fixed a ticking/low oil pressure problem by simply changing the oil 3 times in a 3 week period and new plugs, wires and distributor. obviously needed cleaned out or something. fairly new oil pump. anyway, now its running like a champ, awsome power. 4wd makes a clicking noise after disengagement, I think its a worn auto hub? if i drive it backwards for about 20ft it stops. Now the only problem I have is sometimes it idles wrong. sometimes it idles perfect. timing is set, and idle set to specs. I notice when I drive for about 10-15mins and hit the gas on the highway or maybe starting a hill, the check engine light comes on. when its cold sometimes will almost stall taking off from a stop. rarely actually does stall. sometimes when I start the idle will sit under 1000rpm and then the guage will drop a small margin and then go back up, sometimes over 1000rpm and its not the guage cuz I can hear the motor idling up and down. but this doesn't happen all the time, sometimes it idles perfect, comes off from stops without hesitation. a mechanic told me the IYAC or AYAC motor might be bad??? He pointed to the setup attached to the fuel injection piece on the top of the engine, the piece comes to a bend toward the left tire and attaches to a hose. the piece he was refering to is right before the hose attaches, to the right, and has a black plastic covering. I need to know what this will cost to replace, I've searched for IYAC and AYAC and found nothing. Any help in fixing this idle problem will be greatly appreciated. I love the truck, its running great since all the fixes and I'm just one of them people that can't stand small problems that don't really matter but are annoying. sorry for the long thread. thanks again. oh almost forgot, of course it has the 2.9L 177 EFI engine

 

IAC valve is certainly a possibility. You might try cleaning it out with a little carb cleaner.
With the CEL coming on, pull codes from the computer to see what trouble codes come up. See pulling EEc-IV codes (or something to that effect) in Kenoo's tech info post.

 

thanks for the reply. still can't find anything on any parts sites for IAC valve, is it called something else?

 

Iac Idle Air Control Valve
Also Called Air By-pass Valve

 

thanks for the replies guys.