TJ: High rpm problem... Help

[ECHO]

Im having an issue with the heep and would really appreciate any advice. I just replaced a cracked banks header last weekend and now its having idle issues. When first started, it idles fine at around 900-1000 rpms. After i run it down the street, it starts idling at around 1800-2000 rpms. It runs nice and smooth at high rpms on the freeway. Ive changed the throttle position sensor but it didnt help. The odb reader is showing code p-0108 manifold absolute pressure or barometric pressure circuit high output, p-0306 cyl 6 misfire, p-0301 cyl 1 misfire, and p-0300 multiple cyl misfire. Ive read through several forums online, but it just made things more confusing with ias, egr, tb valves, and maps being mentioned. Thanks in advance for any help or advice.

[Dukes69]

How about vacuum leak? If the intake manifold gasket was compromised when installing the header then it'll cause a high idle.

[ECHO]

Actually it had a bit of a high idle before the header replacement, not just after. Another thing its doing is when i press the clutch to shift gears, the rpm increases instead of dropping. It goes up about 100-200 rpms while pressing the clutch to shift from 2nd through 5th gears.

[Zoobi]

Did you get this fixed?
Just looking at what you wrote for the codes,the map sensor code could be caused by a vacuum leak like Duke said. If it was there before but not as bad, you probably disturbed something that was already having an issue or its just a big coincidence. Check easiest first, look at all vacuum lines starting on that side.
The way I traced vacuum leaks (assuming it is one) Was with a spray bottle with water. Spraying around gaskets with the engine running. When I hit the leak the idle would change slightly. Some people use carb spray. It works better but, if you don't know what your spraying it will flash and could burn things.

Scott

[6spdYJ]

Also, check to make sure that the throttle cable isn't bound up or that the return springs are in good shape and in the proper location. Check the position of the Throttle Position Sensor. If this is off, it can cause high or low idle and performance problems. autozone.com has a good how-to on checking it.

[6spdYJ]

Does it have air conditioning? I have seen the fast idle relay fail or stick. This circuit is designed to increase idle speed and torque to compensate for the compressor load on the engine.

[ECHO]

No, its still doing the same thing. I replaced the idle control valve motor on Saturday and nothing. I tried changing the map sensor today and I noticed the check engine light did shut off but it still idled high. Now its idling up to 3000 rpms when I floor the gas a few times while stationary. My Jeep is not equipped with air conditioning. This is getting really frustrating. I do appreciate the help.

[6spdYJ]

With the engine idling, take WD-40 and spray it around the intake manifold gasket. Listen for changes in the idle speed or stumbling. Avoid spraying it directly on the header-lots of smoke and potential for fire. Any result, change the gasket.

[igofshn]

vacum leak just as stated in the first post.

Instead of WD40 you can use starting fluid or carb cleaner. Spay it around the intake and vacum ports. if the idle changes, that is where you have a leak.

[dirtman13]

x3 on vacuum leak.

You can also use a propane touch to test for a leak. Unlit of course.

[Jerry Bransford]

Your intake manifold is leaking which is very common after replacing the exhaust header. The intake manifold has to be positioned properly over two small positioning studs located on the head and if it isn't, a vacuum leak is the result which gives high engine rpms.

[kirkandsylvia]

this might sound redundant, but yes to all the post above...might be a vaccum leak. But I would check at the back of the intake manifold. There might be a small 1/4 or 1/8 vaccum line that comes off the rear of intake manifold that has a hardened plastic fitting that a soft vaccum line goes into. I broke mine during the removal of the head on my XJ and didnt even realize it till later when I was cleaning up some stuff in the engine compartment. Just my :2: for what its worth.