Hi guys, I have an 89 F150, 4.9, 4 speed, 4x4. The truck has a bit of an idle issue, when I first start it, it will jump to 2000 rpm and just sit there for I'd say about 3 seconds. Then it will idle down to about 1100-1200, stay there, but sometimes jump down to normal idle speed for a second.

I'm thinking maybe the IAC? One of my friends said check the thermostat, but that didnt really make sense to me.

THANKS

Andrew

(just wanted to use that, I mean how awesome is a dancing banana?)

 

its def your IAC or you have a vacuum leak somewhere.

your thermostat in a 89 will have nothing to will the idle. only very late obd2 motors have an ECT(engine coolant temp) sensor that is an input for the PCM

 

most likely iac or vaccum leak. spray carb cleaner around the plenum gasket and throttle body gasket and such and see if the idle changes a little bit. if not then its the iac and i'd recommend you clean the throttle body when you do it.

 

wow wow wow...dont ever clean it with brake cleaner or anything like that. you will ruin it

 

who said anything about brake cleaner? i said use carb cleaner to see if theres a vacuum leak around one of the gaskets. though i guess i should have said clean the throttle body with throttle body and air intake cleaner and a old tooth brush.

 

Who told you that?!?!?

 

im talking about 2003 and later. all obd 3 vechicles use them as well

 

Both your '96 OBDII F-150 and my '95 OBDI F-150 have ECT's, and both of our ECM's rely on the input from them.

 

Yup! You got some wrong info there bud.

 

Try cleaning & relubing throttle linkage /check for potential binds/movement restriction. Idle speeds & durations at start will vary with condition of engine in relation to the external conditions each time.