Engine/Transmission (1998.5 - 2002) Rough Idle - Sometimes

[highland]

I have - for quite some time - occasionally been getting a rough idle. Seems to happen in warmer or hot weather, very seldom in cool weather (like below 50). While it may idle rough one time, the next time I start it, it may be perfectly smooth again. I am now on my 3rd lift pump with 134,000 miles. While I have not checked the pressure, the lift pump was just replaced about 5k back, and it seems to have had no effect on this idling condition. It also does not seem to be a fuel filter deal or fuel quality deal, since I have tried every combination of fuel with/without cetane boost additive, and new fuel filters. It seems to feel fine off-idle in all cases. Any suggestions or similiar experience?



99 QC Auto 4x4

 

[Lordsman]

My '99 has a rough idle at times but I attribute that to bad fuel. It will go away with a new full tank. I'd clean the map sensor, make sure your intercooler/turbo boots are tight and run some injector cleaner(BK44) through with a full tank of fuel. Better be sure your lift pump pressure is good, and all the little mainenance stuff is right.