Rough idle when on Defrost...?

[Lane24]

Does anyone else experience a really rough idle when they have defrost on. I noticed a lot of stumbling, and rough idle, but as soon as I go to floor or panel, the idle smooths right out.

Any ideas on how to remedy this. With the cold Canadian winters on the way in, it's nice to use the remote starter, and defrost those windows in the mornings, but that idle is going to drive me nuts.

 

[Stoned06]

The defrost works with the AC, so I would assume it has something to do with when the AC condenser is running. Try running the AC and see if that makes it stumble also. If so, it might be drawing too much amperage, or the extra load on the engine is just making it run rough. What are your RPM's at idle without the defrost/AC on? You might just need to bump up the RPM's a bit.

 

[Lane24]

Thanks for the response. My old Explorer did the same thing when the AC was low and the compressor kept trying to turn on.... I'll look into that. Forgot about the defrost/AC connection.

 

[JUST4FUN]

check for a vacuume leak most likely inside the truck ,but just a guess
clean the IAC valve ?
check the PCV system for leaks

 

[Lane24]

Replaced my IAC and took it for a run out on the highway. Seems to idle at 1100 now. A far cry from the 400 - 800 range it was in before. Still guessing it might have a bit of a vacuum leak somewhere though. The most common area would be the PCV hosing, or vacuum assembly or whatever it is called that goes to the pcv valve.

Most vacuum leaks on our trucks come from this little assembly.

 

[Lane24]

Update: Still idles like crap... Check Engine light on now... Found the problem!!!! Total vacuum leak. Climbed up into the engine compartment ( damn lifted trucks) and reached way way way back to the firewall and found the leak. getting a new hose assembly in the morning. Here's a awesome link to the problem.
Just had to feel around for it. Mine was just tucked under everything.
http://www.azda.com/ford/ Definately could feel the suck from the crack in the elbow. Replaced the hose, CEL is off, and runs like new!!!