Too little Vacuum? 01 XJ. ONLY when the Jeep is cold (like it has been sitting all night) and I go to start it, it starts but after the starter does it's thing the idle is very low. Only goes to about 400rpm even right after start up. The idle stays low then bobs up and down and sometimes stalls. If I tap the throttle it will jump and usually fall and stall. When the motor is fully heated it runs fine though, even if I start it up again.

I replaced this vacuum line awhile back and did a homemade job using some heater hose. The connectors are the same size as the factory plastic vacuum line. Is this why my idle does this?

 

have you checked your fuel pressure? tried the poor mans prime? cycle the key 2x before starting it next time. listen for the pump to run a few seconds then when it stops, turn the key off and then back on again..let it cycle again, then start it.

i don’t believe your issue is vacuum related. example: i deleted the line going from the front of the valve cover to the air box. i also have a homemade line on the back going to the intake manifold...no issues here.

 

Ever cleaned your throttle body and IAC?

 

You win good sir, cleaned the IAC and throttle body. No further issues. Cheers.

 

Cool. Do that every 15,000 miles.