Still idling real rough

My pos is still running rough when I am stopped in park, drive, and reverse.. It get smooth if I hold the brake and give it a little gas while in gear and when I put it in neutral.

I have been reading up on what can cause this and I am not sure what else to try, I have done Poly Tranny mount, Poly Motor mounts (today) and run some injector cleaner through it, it has new plugs and dist. and a K&N air filter so the tune should be fine. I also have messed with the crank case vent (I believe its called the one coming out from the valve cover to the air cleaner) it was broken when I bought my XJ and now it has a little K&N on it.

Its a 94 XJ 4.0 AW4 It runs strong no check engine lights or smoke.

Any thought or advice would be appreciated
Thanks in advance,
Joey

With the engine off, remove all of the spark plug wires from the plugs, then set them back on the plugs just a touch.

Start the engine, and one at a time pull each spark plug wire completely free of the plug. A missing cylinder will not make the idle worse when the plug wire is pulled.

Post back with results.

joe_peters said:

With the engine off, remove all of the spark plug wires from the plugs, then set them back on the plugs just a touch.

Start the engine, and one at a time pull each spark plug wire completely free of the plug. A missing cylinder will not make the idle worse when the plug wire is pulled.

Post back with results.

Click to expand...

Sounds good I will try it tomorrow at work.

also is it up to date on tune ups and everything? How do the plugs look? are the electrodes squared off sharply (standard plugs, some NGK and AC Rapidfire have a 'needle' electrode)? Are they gunked up with black stuff?

If so, Champion Truck Plugs, or AC Rapidfire (works great in everything I used them in, smoother idle over plain plugs too)

upstream 02 may be bad? I dunno... seems that it would throw a light if that were the case.

No mention made of a check engine light so can we assume there have been none? If there has been, even if for a minute, read the codes.

You mentioned plugs are new but what about cap and rotor AND plug wires?? Wires are often overlooked.

If you don't stumble onto it, never hurts to get a compression gauge and check all cylinders.

joe_peters said:

With the engine off, remove all of the spark plug wires from the plugs, then set them back on the plugs just a touch.

Start the engine, and one at a time pull each spark plug wire completely free of the plug. A missing cylinder will not make the idle worse when the plug wire is pulled.

Post back with results.

Click to expand...

Did it and it made it run worse every time I took a wire off on all six. It should run rough when I pull one off right?

ChevelleSSLS6 said:

also is it up to date on tune ups and everything? How do the plugs look? are the electrodes squared off sharply (standard plugs, some NGK and AC Rapidfire have a 'needle' electrode)? Are they gunked up with black stuff?

If so, Champion Truck Plugs, or AC Rapidfire (works great in everything I used them in, smoother idle over plain plugs too)

upstream 02 may be bad? I dunno... seems that it would throw a light if that were the case.

Click to expand...

I checked the plugs when I bought the Jeep in April and they where good the PO said he had just tuned it.

birchlakeXJ said:

No mention made of a check engine light so can we assume there have been none? If there has been, even if for a minute, read the codes.

You mentioned plugs are new but what about cap and rotor AND plug wires?? Wires are often overlooked.

If you don't stumble onto it, never hurts to get a compression gauge and check all cylinders.

Click to expand...

I had some check engine lights but they where from the speedo not working and that is fixed so the ECU is clear as of now and has been for a while.

Like I said above when I bought the Jeep I check everything, and the PO said he had just done a tune including plugs, wires and Dist. cap. I may see about a compression test it cant hurt anything and is always good to know.

Thanks for the info so far I will keep at it, I am a bolt on bitch Tech at 4 Wheel Parts but when it comes to weird stuff like this I am not the best. I really hoped the Motor mounts would fix my issue but I am not that lucky. Would you guys think it would be cause of the crank case K&N on there I have read mix thoughts on these?

It does have a 189000 on the OD I am just trying to get it to run smooth and good till I can save my pennies to rebuild it but it wont be for a while, like I said it has a ton of power still and start and drives awesome.

Ok, it didn't change when the plug wire pulled so that would indicate the problems is either random, or across all cylinders.

What is the idle speed, in DRIVE, engine and transmission fully warmed up? It should be 700-750 rpm.

joe_peters said:

Ok, it didn't change when the plug wire pulled so that would indicate the problems is either random, or across all cylinders.

What is the idle speed, in DRIVE, engine and transmission fully warmed up? It should be 700-750 rpm.

Click to expand...

When its warm in drive its between 700-800

Check around for intake leaks, try a unlit propane torch.

Will a cylinder with poor compression give the voltage indications that it could be an O2 sensor?