If I unplug the IAC on my 95 should it die. The idles slows down but does not die. If you plug it back in it picks back up. Is this normal or should the truck die?

 

I also forgot to add that if you run the engine up to 1800rpm and unplug the IAC the motor slows down when you plug it back in it speeds up. I thought the IAC had not affect on anything but idle.

 

Your first statement is normal for IAC operation, no the engine should not die. I can't say I ever tried revving an engine up then unplugging the IAC. What issue are you having and trying to resolve?

 

Thanks for your reply. Every since I have bought this truck it seems to have a slight rough idle. It is idling at normal speed just a bit rough. I have changed sparks plugs inspected the wires and cap/rotor. I cleaned IAC as well. There are not codes or CEL. There are only 48,000 miles on the 5.8L and has been garage kept its whole life. I started playing around with the IAC and unplugged it at idle and the idle did not change much at all. I blocked off the throttle body and still could not kill it (it was just barley running though). I checked everywhere for a vacuum leak finding nothing. I then sprayed throttle body cleaner around the black breather on the IAC and it died. If you rev the engine to 2000rpm and plug in the IAC it speeds up. I thought the IAC was for idle only. What is going on?

 

Your probably wasting your time. I've had two f150's with the 351 and both had a mildly rough idle even though everything else was fine. I think it's just par for the course for these small block fords.

I do know that ford actually made an adjustable adapter plate for the IAC valve to fix a hunting idle, because of the oversized ports on the IAC.

 

Thank you. What is the black breather on the side of the IAC? It must let some air in because that is the only thing that was keeping mine running with the IAC unplugged and the throttle body blocked off.

 

What is this "black breather" thing you're talking about, the IAC is totally sealed with nothing but an electrical connection on the solenoid.

 

Yea, what Paul said.......as for rough idle....every one I've seen has done this including mine...I think the cause of mine may be a slobbering injectors, I'll find out soon enough.

 

The "black breather" is the black cap on top of the IAC on my 95. I figured it was a breather anyways. Like I said if the motor is running with the IAC unplugged and the throttle bodies totally blocked it will still run at a very low rpm. The only way to kill it was spray carb cleaner around that black cap as you could hear air rushing in there. I cannot believe that would let enough air in to keep the motor running but it does. I have triple checked for vacuum leaks with no luck. Can anyone confirm that the IAC works off idle as well? Like I said earlier if you run it to 2000rpm and unplug the IAC the rpm drops.

 

I've got a good "What the heck is this?" question like this, but mine is what is the random hot air blower in this areas. My friend has a 94/95 f250 351 that has a weird thing up in this general vicinity that blows hot air. I can't really give a better description. I'll try to get pictures.

 

Sorry to keep this thread dragging on and confusing everyone. So it is normal to unplug the IAC at normal operating temps and on a "healthy" engine and see no change in rpm's? The only reason why I asked this in the first place was because before I changed the plugs if the IAC was unplugged it would die. Now after changing the plugs there no change in idle and still idles fine.

 

when you say "changed the plugs", do you mean the plug that goes to the IAC or the spark plugs?

 

Sorry about that. I changed the spark plugs. I think I figured out why it will run just fine at idle as long as there is no load on the engine with the IAC unplugged. There is a spring in there that keeps the IAC open some if it is unhooked. I know it is working because when you put it in gear or turn on the A/C the idle does not change.