2.5L Wrangler Missing at Idle

[Ryan00TJ]

My 2000 2.5L has developed a slight miss at idle and only at idle recently. It runs fine at all rpms except while idling it has a slight miss ever few seconds. It has become very troubling as I can't seem to find out what the hell is causing it!

Here is what I have done recently to fix it......
1. New Champion Copper Truck Plugs #4412 gapped at .035
2. New Distributor Cap
3. New Rotor
4. New Sparkplug wires. Factory ones were arcing and I thougt that I had found the problem however it still misses.

My TJ only has 36,000 miles. If it were an injector problem wouldn't I notice it at other speeds? Or not have the usual power? Anyone run into a similiar problem? Any ideas?

 

[Dan4510]

The injectors may need cleaning. An injector that has a spray pattern changed by carbon can cause a miss at idle.

That would be the next logical step, I think.

Try techron by chevron. Get the big bottle.

Dan

 

[TheLoneRanger]

A sticking EGR valve will give a poor idle. The valve is supposed to be fully closed at idle, but if it's sticking open that will cause your miss. If there is no MIL lit, then I suggest taking the EGR valve off and cleaning the carbon out of the pintle.....

 

[N2OIL]

Intake leak? Does it change when the engine temp is cold or hot?

 

[Gary Allan]

Okay ..I agree with some of the above. The 2.5 in the 97-02 trim anyway doesn't have an EGR (cam overlap and ignition and injection timing leaves the spent stuff in they cylinder).

If you had a vacuum leak your engine would interpret it as an open throttle and raise the idle.


Try this: Turn the key ON-OFF-ON-OFF-ON (leave on) ..see if any codes appear on your odometer display. I believe if you have NO CODES you'll see "done" in lower case letters.

 

[MNgopher]

I was going to suggest EGR, but it seems Chrysler did the same to the 2.5 as it did to the 4.0l - cut out the EGR valve. On my '88 Cherokee with the 4.0, the EGR was a cause of a rough idle.

I'd go the injector cleaner route next. As stated, the big bottle of Techron Concentrate (not the Pro Guard) would be a good choice. It may be a case that there is enough other stuff going on that you can't feel or notice the same thing happening at higher rpms than idle.

For under $10, it can't hurt!

(For those who don't know, the 4.0L was built off of the specs of the 2.5l, which is loosely based on the old 4.2l. Thus, they share a lot of the same issues...)

 

[Gary Allan]

quote:

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(For those who don't know, the 4.0L was built off of the specs of the 2.5l, which is loosely based on the old 4.2l. Thus, they share a lot of the same issues...)

---

Yes, the 4.0 incorporated the better flow design head that the 2.5 had. This is a strange relationship between the two engines. The 4.2 was the start. The 2.5 came around in (hmmm 82?) ..they hacked out the two WRONG cylinders ....put a 1 piece rear main seal in it ..gave it a different bolt pattern (different trannies, t-case input splines) ..yet kept all the internal hardware the same (valves, rods, pistons, etc.) ..and yet somehow made a superior flow head ..that took a while to get to "big brother".

Go figure

 

[Ryan00TJ]

Yep no EGR on this one. It does it hot or cold so I don't think it's an intake leak. The new wires, cap and rotor seem to be helping some as the miss is now happening every 10-20 secs and not every 5 seconds. Maybe the added spark from new wires is helping. I ordered a gallon jog of Fuel Power and will start with that when it arrives and will report back to let you guys know how it comes.