check for vaccum leak on upper intake up front and center but underneath it, it hides under there, its just a small hose that has a 90 degree bend....but mine had a whole in it and my truck did somewhat of the same thing yours is doin...

 

Well i can tell you after i fixed my vacum leak my truck did the horrible vibrating like your describing but mostly at idle i replaced EGR and IAC and it solved the problem...

 

Miss in engine still there, but not as bad
I still have a vibration in the motor but it doen't feel like a miss. I put the parking brake on and at idle took the vacuum line loose from the EGR pod and there was no change in the motor and it had a little vacuun on the line. It ran smooth. I had my daughter run the idle up just a little I slipped the vacuum line back on the EGR pod fitting and the motor started to shake like it had a miss.
I had mentioned in earlier threads that I had run a compression check and all six were at 190psi and I think that ruled out a burnt valve and that I had found a vacuum line that went to the egr vacuum lines to the plenum on the left of the motor in the back looking from the front of the motor that was delappidated and replaced it and the pvc valve and most of the vibration or miss went away I also tried to see if there were any vac. leaks as you describedunder the plenum, I didn't find any. This vibration only occurs between 10 an 40 mph and in a freewheeling state.
I am thinking it may be a bad EGR
Would a bad EGR make an engine shake like it had a miss at low speed?
Got any thoughts?
BTW: I replaced the fuel filter a couple months ago and just replaced all 3 oxy. sensors,mass air flow sensor,wires, plugs,air filter and coil pack.
My thread is listed under: collinscw miss in engine.
Thanks

 

I am going to replace the EGR but what is the IAC you mentioned

 

okay then after i fixed my vaccum leak i had the vibration like your describing...i had a bad EGR and IAC so i replaced both i think i had 120 bucks for both of them together

 

An EGR function that low in ground speed would tend to make the motor rough.
The EGR is supposed to function by command between certain road speeds and certain other conditions must be present.
The road speeds are usually about 1800 to 2500 rpm in third or overdrive and then if the throttle is relitively stable.
At idle, there is not enough vacuum leaking past the regulator to open the EGR, unless something is faulty.
At higher throttle positions calling for some power, the EGR is closed again.
Any actions different than discribed will cause drivability problems.
It is easy to check out with a vacuum gauge and a hand vacuum pump.
The reason the EGR will cause drivability problems is the fuel is cut back and the ignition timing advances as the mixture becomes very lean and hard to fire by the plugs and coils. This is what causes the problems if it happens when it is not programmed to do so or there are faults..

 

IAC controlls the idle i forget the exact name of it its idle something i believe....my truck through a engine code and thats how i caught it...it's a EASY fix it sits right on top of you intake

 

okay i got my chiltons out for ya.....IAC Idle Air Control that is what it is

 

I am going to replace the EGR but what is the IAC you mentioned

 

Ok,
I think that is the small sensor looking at the motor from the front and on the left side of the plenum?

 

I think you hit it exactly at those speeds it is exactly as your describing. What about the IAC control valve? Should I change it also?

 

sits right above throttle body

 

I personally would change EGR first then go from there

 

I'll do that thanks for the info. I'll see what happens then.

 

Okay let us know how it goes cuz i can help ya out i've pretty much replace my whole entire truck...