Rough Idle in Gear but it's Smooth in Park. Whats Wrong?

[OVERKILL700HP]

I have a 94 X.
Sometimes it idles rough while in gear and when in park it's smooth.
I think it happens mostly when it's warmed up but not sure.
It already has new plugs, wires, fuel filter, thermostat, and been seafoamed many times.
No Vacuum leaks were found.
Any idea's what it could be?

 

[dogfriend]

What happens to the idle speed when you put it in R or D? Does it drop a lot or just a little? If it drops a lot, it might be the infamous IAC valve. It is supposed to let in air at idle to control the idle speed. When you put it in R or D, it is supposed to open a little more to compensate for the additional load on the engine. If it is sticking, then it won't be able to do that and the idle speed will drop.

IAC problems are common with the 2nd gen Ex, but the 1st gen also uses the same type of valve.

 

[OVERKILL700HP]

"Sometimes" the idle will be rough/drop a little when put into drive, when it's warm i beleive.
I forgot to mention that within the last 2 months, i changed the IAC with an AutoZone version. I had an idle problem before and noticed that this improved it. Cleaning the IAC did nothing.
A short time later i remember it coming back.
Is it possible that the IAC is the cause, Would the Ford IAC make much of a difference?

 

[dogfriend]

Your symptoms sound the same as mine when my IAC went bad. After the engine was warm, when restarting the engine the idle would be very low and the truck would stall in R or D unless I kept my foot on the gas. If it is the IAC sticking, you can compensate for it by cracking the throttle a little bit to keep the RPM up.

On my IAC, when I removed it to replace with a new one, I could see a spot (inside the ports) where the valve was shiny because it was rubbing inside the housing. That was apparently why it was sticking; the parts would expand when the engine was warm just enough that the valve would stick. I would look for this on your IAC before replacing.

I don't know if it matters if you have an Autozone part or a Ford part. If you want to try Ford again, you can get the part for a better price from fordpartsnetwork.com.