1990 Comanche Runs Rough

[texasjack]

My 1990 4.0 runs great when it is cold but when it gets to operating temp it has a rough idle.

 

I put new plugs, wires and number one fuel injector.

 

Checked compression and it is 145PSI.

 

And suggestions would be appreciated.

 

Thank you

 

Texasjack

[HOrnbrod]

Check (or replace) the O2 sensor.  I think Cruiser has a writeup in the DIY forum on checking the Renix 3-wire sensor.

[cruiser54]

Probably is it. but the ground for the O2 sensor or it's relay can be a contributor.

 

I would perform Tips 1,3,4, and 5 first. Then test the O2 sensor.

 

Should you decide to change it, use only NGK/NTK