Hi there, this is my first post so excuse any mistakes. I have a 90 XJ, 6cyl, 4x4, that has a few issues im looking to amend. It first started with not passing smog in nevada. It recently had a new cat installed, and failed carbon monoxide at high rpm, by .8%. Since then its had a rough idle, bouncing below 1000rpm and back up. And today it started putting out some black smoke, not too heavy but enough to notice in the car behind me. Ive ordered a new MAP and NGT o2 sensor, but im looking for any more input? any ideas?

 

Have you scanned it for codes?

 

My jeep is pre OBD, multimeter shows nothing out of the ordinary

 

May as well clean the throttle body and IAC.

 

Yep. It's free, and it needs to be done now and then, and it can certainly make a difference.

Also pull your cap and take a look at the contacts, and the rotor contact. Might be time for new.

When was the last time you replaced the plugs? Plug wires?