I posted this a few years ago. I and all the local shops have been unable to solve, so why not try another post?

when the temp gets cool, the idle gets rough. all winter long, runs great in the summer. Replaced van hoses and IAC twice. Can't afford to move to FL, would sure love to fix for Tennessee winters.

thanks

 

Has it started doing this again?

As far as the cold temps....what are they?

How many miles on the truck?

Have you tried running premium gas?

What brand of spark plugs you using?

Have you cleaned or replace the mass air flow?

The condition could be a result of winter blend gas?

 

Has it started doing this again? YES

As far as the cold temps....what are they? < 50

How many miles on the truck? 240k now, but has been doing it 5 years

Have you tried running premium gas? no, bank would not loan money for premium

What brand of spark plugs you using? Motorcraft, changed 1 1/2 year ago

Have you cleaned or replace the mass air flow? cleaned but not replaced

The condition could be a result of winter blend gas? not think so, will do it on cool fall morning but not later in day when temp comes that day, it runs great. temp drops at night and it is back.

 

I see you said you replaced the IAC, have you checked the IAT?

This is only a guess on my part, but if the Intake Air Temprature is being read incorrectly it might cause that issue.

 

No, I assumed it if it worked in warm temp it worked. Has anyone seen the IAT cause cold weather rough idle

 

Ok, I put in a new IAT and the weather warmed back up. Go figure. Will update the post when the temp drops

 

Ok, had a cool morning. Problem was not the IAT sensor, rough idle still there.

Does anyone have another area I could look at?

thanks

 

somewhat new here and just thinking out loud, but here are some thoughts:

i assume the truck is 100% stock? no tune or anything?

1) does it always do it when its cold?
2) does it matter if the gas tank is full or partially empty?
3) any codes or check engine light on?
4) i assume you've checked for vacuum leaks already?
5) have you tried doing a cold compression test?
5a) no funny engine noises (knock, ping, exhaust leak, etc when its cold?)
6) pressure test the EVAP system yet?

just some thoughts that came to mind.

 

i assume the truck is 100% stock? no tune or anything? Yes, stock

1) does it always do it when its cold? yes, always
2) does it matter if the gas tank is full or partially empty? fuel level not matter
3) any codes or check engine light on? sometimes, shows lean
4) i assume you've checked for vacuum leaks already? yes, replace all hoses
5) have you tried doing a cold compression test? not know what that is
5a) no funny engine noises (knock, ping, exhaust leak, etc when its cold?) no
6) pressure test the EVAP system yet? not know what that is

 

Ok, any other ideas? I am ready to R&R parts, just not sure which one. What else could cause a cold weather only rough idle?

 

Winter blend gases can do a toll on idle as well

 

What engine size too?

 

Isn't a lean code a possible symptom of a vaccum leak?

 

Yes, that was my original thought because that is how it behaved (but only in cold weather). I have replaced every hose and fitting I can see as well as removing and vacuum testing the reserve tank. It if is a vacuum leak, it seals itself above 40 degrees and has not gotten any worse in 5 years.

 

Could be the throttle plate sticking. Mine did that and I cleaned the throttle body. When you tried to manually open the throttle it would kinda stick and there was all kind of gunk between the circle plate and intake.

Can't get a loan for premium huh? You know it only cost 3-4$ more every 10 gal... I'm just as broke as the next guy but I skip the soda and candy bar to put premium in my truck.