4.0 Moter issues

ZJjosh · 03-03-2012, 06:26 PM

Hi guys/girls! okay my problem is i just had a 4.0 built for my zj. got it in and now it idles ruff. It goes away at about 1500rpms. any one know what could cause it? I have been over it three or four times checked everything!!!

gactech · 03-03-2012, 07:32 PM

How is the vacuum hoses? Maybe left one off.

**Oldfrog** · 03-03-2012, 10:27 PM

How long has it been run since the rebuild? 10 min or 1 hour or more?
I takes the PCM a little while to adjust itself.

There's probably a lot of oil in the combustion chambers due to the rebuild, which will burn off eventually. ( you might need a change of spark plugs , though )

If it doesnt clear up after 20 min of driving, I'd clean the throttle body and IAC, in case it hasnt been done. The PCM is probably still compensating for the "old" parameters and it's running rich. ( just a guess)

ZJjosh · 03-04-2012, 05:26 AM

All hoses were replaced. The only thing that I might need to change is the
Spark plugs. Everything I've ever read about jeeps is they call for champion spark plugs I put
Ac deco. Idk. I'm going to pick it up today and drive it for a while. We have let it set and run for a couple of hours probably all together since Friday night when we got her fired up.