ok I just about give up

[megadeth]

ok
91 navajo 4.0 ohv 118000 miles
I have been chasing a rough idle drives ok but idle is real rough I have replaced the following
Iac,maf,css,ect,tps,ats. Plugs wires, new heads and all gaskets,timing chain kit,harmonic ballancer, still rough idle . Compession was 160 to 165 all cylinders . What else could it be I almost have a new vehicle now...
Thanks

 

[Dre]

Perhaps you have an air leak somewhere in the vacuum system? Or perhaps seal is broken under an intake manifold?

Open the hood and check for any hissing noise while the truck is running. Follow all lines to make sure there are no holes and that everything is tight.

See attached diagram...

Also you might want to check injectors... might be clogged.

Good luck!

 

[megadeth]

Well repaced intake gasket and all vac lines. While it was tore down I removed eacc injector cleaned tested and replaced o rings and caps. My vac is a little more simple I dont have egr on mine. I am stumped.

 

[Dre]

is it firing on all 6 all the time? perhaps it's a bad coil? have you double checked plug wires? perhaps two of the wires were switched?

sure sounds to me like a bad maf, tps or simple air leak.

Unless it's as weird as bad coolant temp sending unit - not the gauge sensor... computer temp sensor.

Fuel pressure regulator? did you check pressure on the rail at idle? clogged fuel filter?

man there are so many things that could be wrong and yet it could be a simple fix.
good luck!

 

[Derek Greenwood]

Me TOO!

I had just gone though all that as well. New heads all new sensors, ignition oil and module, crank sensor, plugs, wires, maf, CPU, and basically everything. Everything except the O2 sensors. Put 2 new O2 sensors in and everything was magically better. It would idle clean and start when hot and so on.

 

[megadeth]

Just in last two months replaced fuel pressure reg,tps and maf,coolent sensor. No change plugs wires all good and in order. Checked for vac leaks a dozen times had a friend thats a mech look he found no leaks.all test fuel pres vac compresion all good. No codes . I replaced o2 last summer only have one on mine and fuel filter once a year just because. I am really lost .cant believe its still rough. About to loose my mind its become an obsession . Lol

 

[Pollarican]

Be sure to check all the wires heading into the PCM - I had one that shook itself loose and it sounded like the timing was off by a ton - pushed that pin back in and it ran like brand new.

Wouldn't hurt to pull the plugs again just for some background diagnostic info - see if any are fouled and double check the gap to be sure.

Someone mentioned it, but also wouldn't hurt to check the coil using an ohm meter - there are specs in the Haynes that tell you what resistances are acceptable and its a quick 5 minute test.

Are you throwing any codes?

 

[megadeth]

Plugs all look good gap is good . New coil test good pulled pcm wires looked good . Where was your bad wire right at pcm . No codes

 

[Derek Greenwood]

Have you checked for injector seal leaks? Have you had the injectors rebuilt? I bought rebuilt injectors just as a matter of maintainance and the engine did smooth out some.

 

[megadeth]

I pulled all injectors and ran wire from batt with switch shot cleaner in them till got good spray pattern thrn replaced caps and o rings also last weekend listened to them with stethascope all working good. Dont think they would be leaking .

 

[megadeth]

Just thinking few weeks ago I changed out plugs they were white and chaulky turned out advanced auto sold me wrong plugs much hotter plug wondeting if that could hurt o2 I replaced it last year wondering if it could be cooked already... Thanks

 

[Birdy]

make sure the throttle body is clean, and the ports going to and coming from the iac are clean, I've solved a couple problems like this just by cleaning the throttle body. just thought i'd throw that out there.

 

[megadeth]

Thanks but throttlebody and intake clean as the day it was built well entire motor is clean . I only drive it on weekends and spend alot of time in garage keep it all clean and nice I will get it muddy and love to play off road but always clean it back up. Had intake off and cleaned it and tb is new

 

[Birdy]

Do you know where the heads were done? Is it possible that the valves were not ground? When you do you're compression check, what is the first reading the first time they come through a compression stroke? does it have to roll over a number of revolutions before you get to 160lbs?

 

[megadeth]

Heads have new valves and springs , pretty much 160 without having to crank much

 

[Birdy]

Might try pulling vacuum lines from the manifold one at a time and put you're finger over the port, and if one of them smooths it out where ever it goes could be the problem. Except the one going to the map sensor of course, if you have a map. I would also like to know what the problem is, so I'll keep digging to help as much as I can.

 

[megadeth]

I did try that awhile ago when I replaced vac lines but will try again. I have a vac gauge and it reads a stedy 21 psi at idle .

 

[Birdy]

Thinking it must be a pcm issue. I have seen a couple cars here that ran funny and after a dealer pcm update, they were great! Maybe try another pcm? If you were closer, i'd give ya one to try, since i've got 2 of those here that are parts, but they can't be hard to come by. ??

 

[Naasau]

Did you check the connections and wires up at the ICM? Since it's right in front of the battery I've seen a number of them at junk yards that have corroded over time, especially if you've ever had an angry battery. Just checking the connections and switching one out might be worth a giggle, since they're cheap and easy to pull at a yard, and only one bolt/plug.

 

[fastcharlie]

mine had a real rough idle when i first got it, would even stall out at stop signs. it ended up being a vac line and bad plugs. but you said you checked those, so im not really sure..