Hey guys, I have 01 expy with the 4.6 in it. My problem is, when idling in gear the rpm's will drop and the truck will shake, but then the rpms come back and it idles fine. Is that the iac going bad? Also, another problem that has just started is, after the truck sits overnite and I don't let it warm up, when I get going down the road it stumbles, but once it gets up to normal temperature it doesn't do that anymore. Could these be connected to the iac? If not what might be causing them? Thanks, Clint

 

anyone have any ideas?

 

Could be the C.O.P.s. Could be an idividual spark plug. Could be that you need to run some sea foam through the system to clean everything out. Might be the IAC, but when it comes to electrical stuff it either works or it does not. Your idle should fluctuate often if you IAC is messing up on ya. I would try cleaning the MAF sensor and mabye your air filter as well as running some kind of injector cleaner. I would recommend sea foam. Do you have any trouble codes or a check engine light at all?

 

no, there's no cel. I kind of figured the idle issue was probably the iac valve, I just wasn't sure about the stumbling when the engine's cold. the air filter is clean and it doesn't miss or anything it still runs good so I was thinking fuel filter or something on those lines. What's the easiest way to tell if a cop is bad? Thanks, Clint

 

Uhm.. plug a scanner up to it and watch the readings would be the easiest I can think of. But you said it still runs good so it probably isnt a cop. Your fuel filter being nasty can cause it to run kinda crappy, but it would be constantly running that way if at all. I would run some sea foam through it. It can never hurt to clean it out, plus you can get better mpgs.

 

I had a similar problem except the truck would stall out at stoplights. I thought it was a torque converter going out, but turns out the IAC was bad. Had to have it replaced, $500 later the truck runs like new again.

 

Holy crap man! I got mine replaced for $64.

 

No kidding.. paid 56 for mine installed it in the parking lot of Autozone in 10 minutes!

 

I talked to the service guy today and i'm actually taking it in fri. am, he said the stumbling when it's cold is more of a sign of the iac going bad than the rough idle, meaning that the rough idle could just be from the iac being dirty, but doing it when cold could mean the plunger or rubber in the iac is weak or has a hole in it.

 

Ehhh idk about that one. Have you tried taking it off and spraying some carb cleaner or something in there to clean all the crap out..they can get pretty dirty and keep the little "plunger" from wanting to extend to kill idle or retract to apply throttle. If that does not work... you can always just hit the thing with the end of a screwdriver as sometimes that makes it work similar to a fuel pump crapping out. I definitely wouldnt pay somebody to fix it. The problem with a rough idle IMO could only be a few things. Either 1.)clogged/malfunctioning/dirty injectors 2.) a coil pack or cop going out or shorting out. 3.) faulty spark plugs 4.) vacuum leak of some sort which is very common on PCV elbows and such. 5.) dirty or damaged MAF sensor 6.) oxygen sensor readings being out of whack causing your fuel trims to be all over the place.

thats about all I got.

 

Similar problem on my 02 Screw 4.6 only in cold weather it would make a weird popping noise that I thought was coming from my CAI. And at stop lights rpms would go down and the truck would almost die. Replaced the IAC no more problems. I would totally replace it yourself the part is like 50 bucks (autozone) and its located right on top of the motor can't get any easier than that.

 

i would clean the iac valve and im not sure on an 01, but my 97 i used to have, the egr passages were stopped up in the upper intake elbow, cleaned them out, never had that problem again(going dead at red lights sometimes, stubling at low idle, etc...)

 

Also try disconnecting your battery, waiting about 10 or 20 minutes then see if the computer spits out a code. My TPS sensor went bad but the computer didn't spit out a code until I disconnected the battery from doing some other work.

 

Hey guys, thanks for the info on my problems, I know the guys at the FORD dealer and I'm not being charged for them to look at it. They're just running the scan on it to see if it shows anything. He's already told me to go to NAPA to get one as they're alot cheaper than buying from them. I'm a firm believer in staying loyal to a place and they'll help you out if needed. I also already cleaned the iac 2x and there's no difference, so I'm just waiting to see what I find out fri. am. Thanks, Clint

 

Have you cleaned the MAF yet? If you use an aftermarket oiled air filter such as a K&N, this is essential periodic maintenance.