Not smooth (not exactly rough) idle on Jeep GC 2000...

[mvbighead]

Alright, this has been going on a while, and i have yet to be able to figure it out.

Basically, when stopped at stop lights, etc., if I watch the RPMs, they tend to stay at 600rpm for the majority of the time, but flutter up and down roughly 50rpm from time to time.

Based on some comments in this thread:http://forums.anandtech.com/showthread.php?t=2210119&highlight=rough+idle

I figured I'd look over the IAC and throttle body. I took it apart, re-cleaned the IAC and also sprayed out the opening as well as wire brushed it. It wasn't that bad, but it is perfectly clean now.

Problem is, I still have the same problem.

Next thought was cleaning the O2 sensors, replacing if necessary. I have not found a vacuum link, but I am no expert there.

In any case, other tips or suggestions are welcome and appreciated.

2000 Jeep GC 4.7

 

[SpatiallyAware]

When was the last full tune up? Plugs, wires, PCV valve, fuel filter at minimum. Look online to see if there are other parts that need replaced during sched maintenance.

Also spray contact cleaner into all connectors for IAC, MAF, and fill with dilectric grease.


Usually if an o2 sensor is bad enough to cause stumbling it will also throw a code.

Check for vacuum leaks.

 

[iamwiz82]

I was going to say this is normal for the 4.0, but I have no experience with the 4.7.

 

[mvbighead]

Just did the fuel filter a week ago (forgot to mention that bit).

Replaced plugs when I first got it (little more than a year ago), but didn't do wires.

Thing is, it has always had this idle thing going on. Never been serious... just annoying.

So PCV valve and contact cleaner, dilectric grease... will do.

I suppose the IAC could be bad, right?

 

[mvbighead]

Also, looks like plug wires aren't used. Instead, coil packs are used... at least, from what I've read, and the fact that I cannot find plug wires for it anywhere. (Yes, I am pretty green when it comes to this.)

I suppose I could have a bad coil, and could test each to see. May have to go that route, but that might be another weekend project.

Problem is, it seems to run just fine at all speeds other than idle. It just flutters when idling. It doesn't seem to be missing.

 

[mvbighead]

Well, just replaced the PCV valve. New one fit a lot tighter than the old one.

Also, it seems the old one was a bit "gummy." The new one rattles about freely, the old one seemed to have some gunk on the rattling part, which maybe caused it to catch just a little to produce the slight awkwardness in the idle. EDIT - The gummy one still rattled, it just wasn't as free as the new one.

I'm hopeful anyway. Just need to go drive it a while and see how much that helps.

 

[Throckmorton]

If it only happens when the engine is warm, could be heat soak. Something to do with the injectors getting too hot because of underhood temperatures. Not sure if the 4.7 is susceptible though.

 

[mvbighead]

If it only happens when the engine is warm, could be heat soak. Something to do with the injectors getting too hot because of underhood temperatures. Not sure if the 4.7 is susceptible though.

I can't be 100%, but it seems to happen immediately. Pretty sure I checked one day after simply starting the car, actually after I had just cleaned the throttle body and IAC opening and IAC plunger.

And, while it isn't a major rough idle, it simple isn't constant as it is in every other car I've been in. 600RPM for 15 seconds, bumps up to 650 then down to 550 within a couple seconds, then smooth for 15 seconds, etc., etc., etc.

Just adding additional clarification if it helps you come up with an idea that is plausible.

 

[IcePickFreak]

Do you have access to a scanner? Sounds to me like a coil pack is on it's way out and you're getting random misfires on that cylinder. If you have access to a scanner to see which cylinder is misfiring, you can always swap the coil pack with another cylinder and see if the misfire follows it to be sure it's the coil pack. If it's sporadic enough it won't throw a CEL.

 

[mvbighead]

I do have a scanner... though I have yet to do something quite like that with it.

I'll have to see if I can figure that out.

For reference: http://www.amazon.com/INNOVA-3100-OB...3560342&sr=8-1

The above scanner is what I have.

 

[SuperSix]

You would probably get a CEL for many if the issues you mention above.

A scanner will help tell you if the IAC/TPS/etc is set correctly.

 

[mvbighead]

Many issues? I thought I only mentioned one. Could you elaborate?

 

[crosshairs]

The 4.7 engines are known for bad TPS sensors ..it will not set a code or put the light on because its not actually going out of spec....Its just putting out an erratic voltage.
Open the hood and grab the sensor with the engine idling in park...and try to move it up and down a bit....not opening the throttle but up and down...if the idle fluctuate even a little bit, its bad.
The condition you are describing is exactly what they do when they go bad

if you had access to a scope, you could see the voltage change as you wiggle the sensor, but without that, you have to rely on the idle fluctuating ...

 

[mvbighead]

The 4.7 engines are known for bad TPS sensors ..it will not set a code or put the light on because its not actually going out of spec....Its just putting out an erratic voltage.
Open the hood and grab the sensor with the engine idling in park...and try to move it up and down a bit....not opening the throttle but up and down...if the idle fluctuate even a little bit, its bad.
The condition you are describing is exactly what they do when they go bad

if you had access to a scope, you could see the voltage change as you wiggle the sensor, but without that, you have to rely on the idle fluctuating ...

Thank you very much for that tip.

I did read some threads (after you made this suggestion), and the problems most seemed to suggest were way more extreme than what I am dealing with. However, if this PCV valve doesn't do the trick, TPS will be my next step.

 

[JeepinEd]

Thank you very much for that tip.

I did read some threads (after you made this suggestion), and the problems most seemed to suggest were way more extreme than what I am dealing with. However, if this PCV valve doesn't do the trick, TPS will be my next step.

I had the same issue on my Jeep. It started out with very minor idle fluctuations, but over time, it go progressively worse, until the engine would shut off while driving. I bought a new TPS at autozone for around $40 and in 5 minutes the problem was fixed.

 

[mvbighead]

Gonna grab a new TPS today most likely. Idle still flutters.

Looks like it's $37 at the local parts store:
http://www.oreillyauto.com/site/c/d...1381430_1898&keyword=throttle+position+sensor

 

[mvbighead]

Well, installed the new TPS as well as an air filter.

Still seems to flutter. Maybe not quite as much, but enough that I can see it. Hmmmm.

 

[IcePickFreak]

Were you able to check for misfires? Looks like the scanner you have doesn't have live data, I'm guessing that includes 'misfire history' as well since thats still essentially live data... ?

I'd still be suspecting a bad coil pack.

 

[LTC8K6]

http://www.wjjeeps.com/tsb/tsb_wj_1800101.pdf

Only TSB I found that might apply, but it's likely already been done.

 

[mvbighead]

Were you able to check for misfires? Looks like the scanner you have doesn't have live data, I'm guessing that includes 'misfire history' as well since thats still essentially live data... ?

I'd still be suspecting a bad coil pack.

I am going to have to see if i can test each pack manually. See if I can spot a difference.

Yet another weekend project.

 

[LTC8K6]

What plugs did you put in it? Sometimes these Chrysler V8's are plug sensitive and you have to use the OEM plugs.

 

[mvbighead]

What plugs did you put in it? Sometimes these Chrysler V8's are plug sensitive and you have to use the OEM plugs.

I read that when I was buying them. I can't recall specifically what they were (20k miles ago) but I thought it would help at the time and it didn't really make the problem any better or worse.

Unfortunately, I don't have an answer as to the specific brand, but I went according to the WJ Jeep site for brand and gapping. Nothing above or beyond what was recommended.

 

[LTC8K6]

Well, the coil packs are a good place to look. Could be a wonky IAC valve too, even though you have cleaned it.

Maybe +-50rpm is the best it can hold? :biggrin:

 

[mvbighead]

Well, the coil packs are a good place to look. Could be a wonky IAC valve too, even though you have cleaned it.

Maybe +-50rpm is the best it can hold? :biggrin:

I was afraid someone might actually make that remark.

Guess I'll be popping off coil packs and testing resistance and such. I would definitely not be interested in just replacing those willy nilly, as 8 x 14 (cheapest cost from RockAuto) is not a cheap part swap that is easy to justify.

 

[sontakke]

Your scanner does NOT have most of the features a scanner is supposed to have. You need following features which are missing from your code reader.

Enhanced SAE Diagnostics (J1979 & J2190)
View and Record Enhanced OBD2 (1996 and above) Live Data

With Live Data, you would have been able to diagnosis it further and easier.