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Forum Home > Modifications > High idle issue - TJ w/2.5L

Posts: 947

Just some information for other 2.5L owners out there:

Lately I have noticed a sudden increase in idle speed. I didn't think much of it until last week when she suddenly wouldn't idle below 1800 rpm! When driving down the road, she would stay around 2500 rpm and then settle down to a minimum of 1800.


What's weird is that when started cold, she would idle just fine. After reaching normal operating temp, the idle would increase drastically. I also noticed I now had an exhaust leak.


I did a search online, and decided that the first thing I needed to do was look for a vacuum leak. I found a port on the bottom of the intake below the throttle body that was open. I don't know what was supposed to be on there, I couldn't find any hoses laying around that was disconnected. I finally made a cap for it. I have no CEL so I'm hoping nothing is unplugged. Perhaps a cap had come off it. The port was shiny and and not muddy like the rest of the engine, so it hadn't been uncovered for long.


After capping the open port, the idle settled down a bit, but not much. I then unplugged all sensors on the throttle body (TPS, MAP, IAC) with no change. Then I noticed that a bolt was loose on the exhaust manifold. I checked the rest of the manifold bolts, and found three that were loose, and one that was missing! I installed a new bolt, and tightened the rest, and voila! No more high idle and no more exhaust leak.


The bolts on the exhaust manifold have large washers that also clamp on the intake manifold. One bolt clamps both the exhaust manifold and intake manifold at the same time.


If you have a 2.5L and experience a high idle coupled with an exhaust leak, check the manifold bolts first! It really could be that simple.


95 Chevy Tahoe 2 door, 6.5L turbodiesel, 285/75R16 Kenda Klever M/T's on Toyota steelies, some other goodies.  Overlanding Fun

March 13, 2012 at 4:18 PM Flag Quote & Reply

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Posts: 186

great diagnostic work, computer controlled fuel injection does weird things when it senses a rich or lean condition, it will compensate for it no matter the problem and sometimes with bad results

March 23, 2012 at 12:55 PM Flag Quote & Reply

Posts: 947


Now I have a new problem: spitting and sputtering / rough running, along with a CEL that shows a code P0121 tps circuit error. 

I replaced the TPS a couple of years ago chasing a similar problem.  I discovered that it was actually a faulty clock spring in the steering column that was shorting out the shared 5 volt reference circuit.

I'm hoping this time that it's just due to excessive moisture.  She's been sitting outside all week in this rain we've been having and has gotten soaked really good.  The hard top is on, but it still allows water to leak in, and she's never sat outside in this much moisture before.

I'm going to get her in the shop and open her up and let her dry out for a few days...hopefully it clears up.


March 23, 2012 at 2:16 PM Flag Quote & Reply

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