I've noticed when the truck warms up when idling and the t-stat opens and the water pump kicks on my truck starts to rumble. Feels like it drops the RPM's down a few hundred and shakes a bit.

I will investigate further today cause I have some errands to run after work, will find out if its leaking but I doubt it is. Any other ideas of what could cause this would be great.

Also, is there a good how-to on how to change it out on a 4.0? Google seems to let me down and I can not find anything.

 

what do you mean when your water pump kicks in? if the engine is running so is your water pump

 

I meant the fan. Its funny cause it will only do it on the morning when its cold or when there is alot of moister in the air. If its sunny and warm it does not do it.

 

This sounds kind of familiar to what my 2000 contour svt did to me. It ended up being the air idle control valve.

 

Will try to clean it and see if that helps. I've been leaning towards the fan clutch cause it seems to drag the RPMs down when the fan kicks on. Is there anyway to confirm this? Free spinning the fan with the truck off wont help cause it wont be engaged.

 

of course the fan hub will drag the rpms down. it is putting a load on the engine. but it is either on or off, there is no way for it to meter itself to only come on part way. it is not a fan issue. it sounds like the iac can not adjust properly when load is applied to the engine to adjust the air in for rpm to stay the same

 

I will clean it today after work and report back. Like I said it will only do it in the morning, don't know why.