I have a 1998 ford expedition with the 5.4L 4x4, My engine light came on, and maybe the next day i went to start the truck up and ut reved up to like 3000 rpms for a hot second and dropped to like 500 rpm's, At a light the idle lopes up and down like it wants to cut off, theirs no problem with acceleration, their are times on the beltway the truck will go as if i have my feet on the gas when i dont, and when placed in the Park gear the idle will shoot up on its own to like 3000 rpms.

 

Sounds like dirt in the throttle body or a bad IAC.

Get the codes read at Autozone and post back what you find from them.

 

I have noticed a loud Hisssing sound, could someone tell me a easy way of locating a vacumn leak

 

No real "easy" way as some can be hard to find.

Spray some carburetor cleaner in the area (not too much). If the idle goes up, you found the problem.

 

OK... we have another case of disappearing posts. I would really like to know what happened to the reply i posted here. I just got an email saying that someone had replied to this thread that I was subscribed to and I remember posting to it, but it is no longer here. Why is this? Somone needs to come up with an answer for this.
Billy

 

Billy:

There has been a tear around here to edit posts due to content, perhaps something you said was mistaken and deleted?

Just an idea, not saying that is the case per se.

There are still problems with the software, sometimes my responses time out, sometimes it takes too long to access a post to reply, etc.

I wish they would lick this problem and spend less time bickering about policy and post content

(A whole other discussion. LOL).

 

Wel still having problems with the idle sticking and loping, i went to get the code read but for some reason my data link port isn't working. I guess i will have to take a hunch and purchase the iac valve, is their any way to test the valve?

 

Use autolibrary below to guide you.

 

Problem fixed, was a vacumn line leak behind the IAC control valve

 

NICE FIX..
I WAS GOING TO ADD TO FIND A VACUUM LEAK, ESPECIALLY IF U CAN HEAR IT, TAKE A SPRAY BOTTLE WITH SOME WATER IN IT AND SPRITZ AROUND THE AREA U ARE HEARING IT, SHOULD START TO GURGLE WHEN U HIT THE LEAK...

 

NICE FIX..
I WAS GOING TO ADD TO FIND A VACUUM LEAK, ESPECIALLY IF U CAN HEAR IT, TAKE A SPRAY BOTTLE WITH SOME WATER IN IT AND SPRITZ AROUND THE AREA U ARE HEARING IT, SHOULD START TO GURGLE WHEN U HIT THE LEAK...

 

Good job, glad it was simple.