2000JGC

This is on a 4.0L engine. When it's first started, it idles poorly, misfiring often until it gets warm. I have changed the spark plugs and the coil rail. I have also removed and cleaned the throttle body and the IAC valve. What am I missing? I have been pulling what's left of my hair out trying to figure this one out. Can anybody offer some advice?


Thanks in advance!

2000JGC

Nobody???

Bustedback

Check engine light on?

2000JGC

No CEL's, no stored codes, either.

Bustedback

Check the fuel pressure. You have any way of reading the data stream?

Don Miller

You say it is 'missing' badly when cold .. is it missing, as in loss of spark to cylinder(s), or is it simply running rough?

In anticipation that it is not ignition spark, check for loose intake manifold bolts or bad intake gasket/seal. Could be sucking air until the joint expands with increased temperature.

Also, throttle body should have gasket under it .. I have seen cases of no gasket being there on more than one vehicle.

Give more information and specifics and others may be able to help identify the problem.

And I agree that the CPS can be a problem, not sending a pulse with every rotation until it warms up (thermal defect). Checking for vacuum leaks costs less than changing the CPS, so fingers crossed.

2000JGC

I guess you are correct, it is running rough until it warms up. Not terribly rough, but much rougher than my 2011 Ram. I had a 2001 GC years ago, and it ran smoothly when cold.


What is a data stream, and how do I access it? What should I be looking for?

Bustedback

I just worked on a Dodge truck the other day at work that would start up and idle rough for a few minutes before smoothing out. I replaced the fuel pump and it improved. I replaced the fuel injectors because I suspected one or more were leaking. The oil smelt like gas and the level was high. The injectors took care of the problem.