Occasional vibrations, idle speed not steady, and interior vent problems.

[phxZ31]

1) My feet vent setting and my mix-door don't seem to be working properly. With heat of full blast, sometimes I get blasts of chilly air, and the feet vent doesn't seem to be fully engaging, as about 50% of the air blows out the defrost vents up top.

2) Idle speed slowly oscillates up and down by a hundred RPMs or so. Occasionally the engine will vibrate for a few seconds and the RPMs will move up a couple hundred RPM, then it drops back down and stops vibrating.


I suspect a vacuum leak, but I'm not sure. All of the vehicles I've been familiar with have all used a MAF to meter intake air, and so vacuum leaks cause all sorts of unmetered air problems. The Jeep doesn't have one, so I'm assuming its got a MAP sensor in the intake manifold. Will the Jeep idle funny and get poor gas mileage if it has a vacuum leak? It would make sense, since both of these issues popped up at the same time, but I'm just making sure.

 

[birchlakeXJ]

Always post the year and engine of your XJ for the most accurate responses here.

The idle hunting could be due to a dirty idle air control. Cleaning it is a good first step to see if you can restore idle quality. I'd start there. Here's a procedure...
-----------------------------------------------------

Cleaning the IAC:
1. Remove the IAC with a torx 15 driver (2 bolts)
2. Gently wiggle out the IAC from the throttle body
3. Clean the IAC with throttle body cleaner (not carburetor cleaner ) Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle as it is fragile and you can damage it pretty easily
4. Also clean where the IAC seats in the throttle body with the same throttle body cleaner
5. Consider cleaning the entire throttle body itself as long as you’re at it
6. Reinstall IAC and check idle quality

 

[phxZ31]

Thanks. I should just add my Jeep in my sig. For the record its a 2000 4.0L

I'll clean out the IAC tomorrow and post back on the results.

While I'm here, do you know where the vacuum lines that control the heater/climate system connect up to the intake manifold?

 

[Ecomike]

Your problem is not the IAC, yet. You have one or more vacuum leaks for sure. The MAP sensor should be on the firewall if they did not move it by 2000. There are vacuum lines all over the engine compartment, and in and around the dash for the damper doors. Most vacuum leaks are under the hood. Sorry I don't have the Yr 2000 line drawing, just follow all the vacuum tubing under the hood, it goes everywhere even to a vacuum bottle hidden in the end of the front bumper, passenger side, to the brake booster, valve cover CCV line, MAP sensor, intake manifold has several connections, one on the throttle body lower side, one on the heater valve one on the air filter housing thermostatic control.....