Engine gets slightly rough idle after warming up?

[jthomas194]

Engine 1992 4.0l gets slightly rough idle after warming up?

I have been looking through the posts about what could cause a rough idle, but i was just wondering if anyone had any other ideas as to what could be causing my engine to go from 1000rpms when just started to 700-800rpms once warmed up.... is this just normal for an older engine (92 4.0l with over 100,000)... the roughness is noticeable enough to shake ur seat a bit, but it still keeps idling at that range... it kinda feels like it is constantly trying to catch itself from dying, but only in very short drops in rpm... like 800-700rpm and back, not 800-200rpm and back... im am kinda leaning towards the lower intake gasket... the truck has new plugs and wires which appear to be good... iac valve was cleaned and seems to be functioning.... havent check the maf or changed air filter yet.... but it doesnt seem like it would be the maf if it was only slightly rough.... i want this damn truck idling at a steady constant rpm... let me know... thanks.

 

[jthomas194]

Well, I just cleaned the MAF sensor.... seems like it is idling much better.... gets to about 800rpms and holds there.... it is much smoother.... we'll see if it stays this way....

 

[jthomas194]

ok well.... cleaning the maf didn't do the trick... i have read that tightening the lower intake manifold bolts can help eliminate a rough idle... guess we'll see what happens...

 

[niterider]

egr valve, replace it

i've had 2 ranger 4.0's that did the same idle. plug the egr and see if it idles right. if they rot on the bottom side thats it. i had mine replaced with a new tube its running fine. ford mechanic says they rarely need bottom intake gaskets

 

[jthomas194]

niterider thanks for the reply.... i will definitely check that.... thanks for the info on the lower intake gasket....

 

[jthomas194]

well.... i could not find an egr valve on the upper intake manifold.... it is right by the throttle body on my taurus so i figured i would look around there.... nothing.... checked all around the intake and there doesnt look like there is a spot to even put one (i dont have the manual for the egr system).... could mine just not have one... it is a 92, and the parts catalogs sell a valve for that year.... anyways, i also tried to tighten the intake bolts but it was a no go... my swivel sockets and extensions couldnt make it to all of the bolts, i would have to move the upper intake and some other stuff just to tighten them... and if i did all that i might as well change those gaskets (upper and lower) and my valve covers.... as well as replace the old valve seals and some new pushrods... any advice on that stuff would be great... i have a shop manual and it all looks pretty straightforward, but im sure you always encounter bumps along the road, and advice on those "bumps" would be awesome... best places to buy quality replacement parts?

 

[niterider]

my egr is on the left exhaust manifold

it is a 96, maybe thats the difference?

 

[jthomas194]

ok ill check there.. thanks