Engine starts easy but runs rough.

Tree top flyer

New Member
Supporting Member
Jun 28, 2021
Minden, Nevada
I have a 1989 YJ with a 4.2L engine. In the early morning , it starts easy and the RPM's come up right away. But after a minute, it idles so rough, it sounds like it is firing on only 4 cylinders.
After it gets up to temp. (approx. 170-180), it runs fairly decent, starting out, and fine at higher speeds. At stop lights, if idles rough, and after stopping, it restarts hard, and requires multiple cranking efforts. I have replaced the plugs, reset the timing, and adjusted the idle down to a lower RPM. It has an MSD ignition and a Clifford Performance intake and Weber Carb, with Clifford headers and a mild Howard Cam. I can't find the problem. Help!!
EGR valve worn out or stuck open a bit is a place to check. Adjusted the idle down? how high was it idling? better check for vacuum leaks as well under the carb and the manifold to head connection.
I recently cleaned IAC Valve which is a 20 minute job, actually replaced it but the 3rd party one was not quite right, so I replaced the orginal cleaned one. Idling at stop lights nicely.