idle issue

[s2gots]

So ive searched the site, and tried the remedies mentioned, but to no avail....here is the issue-vehicle in Park, idles just fine. When the truck is in any gear, and at a stop, after a few seconds the RPMs start to bounce up and down, like its going to die and then gasps for air...and it will do this until I take off again. Sometimes, itll recuperate on its own and idle normally while stil at a stop. It does it when full, half, or empty on fuel. But it does not do it all the time. I would say 6 out of 10 times. At all the cruising speeds, it drives fine, no hesitation, stumbles or anything. Just when in gear and brakes applied. I have changed the fuel filter, ran injection cleaners, and sea foam through the tank, changed the air filter, and changed the air idle control module. I have also cleaned out the throttle body with TB cleaner and a rag as best I could. I plan on sea foaming the top end here in the next few day. Oil has been changed recently. I will be also changing the plugs and wires. Im hesitant to believe its the plugs, or else it would idle like that all the time. Ive read what I could in the searches, but I now need some professional advice...or if someone had this same problem, how did you fix it???

 

by the way,its a 1999 2500 6.0 4x4 with 130k

 

TIA

S2gots

[s2gots]

might this be vacum related??

[Chanks7]

Sounds like a vacuum leak issue......is the check engine light on? How long has this been going on? long enough to set a code? Does it seem worse when engine is cold, hot or same?

[s2gots]

Thanx for the reply chanks7, Its been going on for a while, at least 3 weeks, so if there were any codes to throw, they should have come out by now, I also scanned it for any previous or stored codes, and none were found...no check engine light. Now that I think about it, it seems to only happen after the truck has reached normal operating temps...when I first start in the mornings and go, It doesnt do it, but a half hour later when im in stop and go traffic, it happens....hhhmm

[Clavin78]

might this be vacum related??

 

 

It is a vacuum leak...get a vacuum test done to prove me right or wrong, but most likely right

[cbxeric]

One more thing to consider is that your transmission might need a software update. there is a T.S.B. about some transmissions causing the engine to surge/stumble when put into gear or when stopped in gear.

Just one more thing to consider.

 

Good luck. Eric.

[s2gots]

I will try the vacuum test..how can I do this myself?? also, Any specifics on the T.S.B? What do I tell the dealer, just update the program?

[Valsport]

correct me if I'm off target guys, but could it be a contaminated egr unit? if it's letting in through too much or too little exhaust gas, idle will stumble.

[s2gots]

well, the egr unit does look pretty bad from the outside...almost looks like its corroded, but still in tact....

[roy67ss]

well, the egr unit does look pretty bad from the outside...almost looks like its corroded, but still in tact....

I have found chunks of carbon stuck in the EGR valve that prevent it from completely closing and producing erratic idling. Worth checking out anyway.