My 89 cherokee Auto 4.0, 240k miles. Has a low idle when I come to a red light, almost as if its going to stall. reads about 300rpms on the tach.. how do i go about chasing this issue? Thanks-Paul

 

The one piece of hardware most important in maintaining a decent idle (750 rpm or so)
is the idle air control.

Have you tried cleaning that yet? Clean the throttle body as long as you're at it....

 

I have a 89 and i replaced the idle air control valve and it didn't help with a low idle.... Replace the orifice towards the back of the valve cover. That will help a lot, when it gets plugged the idle lowers quite a bit. x2 on cleaning the throttle body.... a good cleaning can help a low idle... Also run some fuel cleaner through the jeep. when i rebuilt the jeep i had the throttle body and intake manifold (as well as the heads obviously) thoroughly cleaned and it helped with the low idle, but didn't solve it by any means. I got neon injectors (which were actually clean unlike my stock ones) and it completely solved my low idle. So start with the easy stuff. new orifice, clean the TB, and run some injector cleaner and it can go a long way to help the low idle. If that stuff doesn't work try the Idle air control valve. Just my 2 cents.