Stumped on intermittent idle problem

[packmule1911]

Every 10-20 starts or so the Jeep fires up very roughly. It never happens cold, and usually after a 5-15 minute stop for an errand. Runs really rough for a minute or two, and does not respond to tapping the pedal.

IAC valve has been removed and cleaned.
Connection to IAC has been cleaned with electric cleaner.
New plugs.
Intake cleaned.
Two instances of check engine light from this behavior: #3 misfire, and then a generic misfire code later.
Dealer sucked a can of M44 top end cleaner through the system.
Have run a bottle of Lucas with each tank since.

Running out of trial and error money right now so I'm hoping one of you folks has some experience to share. My wife won't drive it until this is resolved and she's missing what I traded for the Jeep over this as well.

Thanks for the help.

[packmule1911]

Forgot to add: yesterday when this happened, I tried tapping the pedal anyway, and I got a couple of tiny popping "backfire" sounds from the engine bay. At least they didn't sound like they were from the back end.

[4.3LXJ]

Might check that throttle position sensor. Any codes or CEL?

[packmule1911]

I don't know that part, but I'll be learning I guess.

I don't recall the code numbers but the first check engine code was for cylinder 3 misfire, and the second was a general misfire.

Don't know what a CEL is. More to learn.

[packmule1911]

A TPS isn't expensive. Any particulars around installing it?

I read an article on testing a TPS with a multimeter. I have one, but electrical stuff is not my strong suit.

[4.3LXJ]

Well, CEL is shorthand for check engine light. Got one on?

[packmule1911]

Duh. Sorry.

Yea, the light has been on twice. Cylinder 3 misfire was the code the first time, and a general misfire the second time.

The CEL did not come in from the occurrence yesterday and remains off now.

[4.3LXJ]

Not having a CEL makes it a little tougher. One more question or two. How long since the upstream O2 sensors have been changed?

[packmule1911]

I've had it a month and never changed any 02 sensors.

When it starts this way, if I set there and let it idle a few minutes it smoothes out just fine. When it starts right, which is most of the time, it runs really well at 750 rpm idle. Maybe some slight fluctuations, but slight.

[4.3LXJ]

Since it straightens itself out when warm, I think at this point that you either have a temp sensor problem, which I think is very slight. I think that there might be a slight TPS problem, but the main thing at this point is probably the O2 sensors, which no one ever changes until they fail completely

[packmule1911]

It only does this when it's warm, but straightens itself out after a few minutes idling when it does this. It's never done this when cold.

What does a completely failed 02 sensor act like.

[4.3LXJ]

Runs rough, stalls or horrible gas milage

[packmule1911]

Looks like the issue is the "heat soak" problem:

TSB 1803103 - 4.0L ROUGH ENGINE IDLE AFTER RESTART FOLLOWING A HOT SOAK
Date: 09/05/03 (supercedes 1802702 dated 09/06/02)
Model Year(s): 1999-2004

Description: NOTE: This bulletin applies to vehicles equipped with a 4.0L engine. This bulletin involves the installation of a fuel injector insulator sleeve.

Details: Customers may describe a 20 to 30 second rough idle following the restart of a heat soaked engine. This condition may be most noticeable when the engine is restarted following a prior 10 to 20 minute heat soak in hot ambient conditions of approximately 32 C (90ºF) or higher. This condition may be consistent with short city stop-and-go driving trips and can be aggravated by the use of fuel with a high ethanol content. Depending upon various conditions a MIL may occur due to DTC P0303 - Cylinder #3 Misfire.

This condition may be caused by heat from the exhaust manifold that following engine shut down migrates to the area around injector #3 and causes fuel vapor to form within the injector. This in turn may cause a momentary misfire of cylinder #3 until the fuel vapor is cleared of injector #3. The insulator sleeve lowers the injector #3 temperature to a point below which the fuel will not normally vaporize.

If vehicle exhibits a rough idle, and if a misfire of cylinder #3 is observed following a 10 to 20 minute hot soak, perform the Repair Procedure.

Parts required:
56028371AA Ignition Wire Shield

Repair procedure:
1. Cut insulator sleeve, p/n 56028371AA, to make two (2) insulator sleeves about 25-30 mm (1 in.) in length. See diagram.
2. Install one sleeve around injector #3, with the slit on the upward facing side of the injector. Install the other sleeve with the slit on the downward facing side of the injector.
3. Confirm sleeve is flush to intake manifold surface around injector.
4. Check injector #3 wire and ensure that the injector is rotated to a 2 o'clock position.

[packmule1911]

OK Folks.

If I've got insulation on top of the intake manifold, and heat resistant tubing about the number 3 injector (per the TSB), and I still get some heat soak problem behavior, what's left to try? Do new injectors work as an ultimate fix for this issue?

If injectors will work, do credible reconditioned ones work ok? I understand that there are upgrades to be done with the injectors (Neon, Ford, etc.), but which do folks like the best? I like the reconditioned price.

[XJ Wheeler]

I've heard of people using heat shielding on the underside of the intake manifold to keep radiated heat from the exhaust manifold/header down some. Although, it would be next to impossible to install it with the intake installed.

Sent via messenger pigeon - i talk, he types.

[4.3LXJ]

A fellow who used to be on this forum cured it by hooking up a fancy timer on the efan so it would come on when the engine was shut off. Cooled the manifold enough to keep the gas in the line from bubbling

[packmule1911]

I don't want to take much of anything apart to fix the problem. I've heard of folks painting their intakes with something like header paint that deflects heat.

If at the end of the day, the problem is that the ejector itself is vulnerable to heat, wouldn't changing the ejectors solve that problem, and allow the realization of an upgrade as well?

Here's what it looks like now. Tubing per TSB, and insulation by former owner.

[packmule1911]

The split tube isn't cutting it. It will still exhibit the same behavior, albeit less often, even when it's in the 30's like it is today.

I'm not sure that the insulation on the intake is doing anything other than interfering with heat displacement. It's flimsy and loose and appears to have been there a long time.

I was thinking to finding some heat resistant tape to wrap around the injector body.

This is a common problem, and I'm wondering what else folks have done and had success with.

[4.3LXJ]

You are going to laugh at this, but wrap tin foil (Nickyg where are you?) around the fuel line and injectors. Use multiple layers and make it a loose wrap. You might be surprised

[Pookapotamus]

http://tapatalk.imageshack.com/v2/15/02/10/a7b3e8b995834fdac5b6146ef0df6713.jpghttp://tapatalk.imageshack.com/v2/15/02/10/520ed1d5dd28574af55074d2ff8a80b4.jpg
I used an adhesive wrap, then bent a shield and wrapped that as well.

This really helped to keep my fuel rail temps down.

[XJ Wheeler]

I think replacing that shielding that is probably original with something new and possibly more effective (you would think they would have made advances since the millennium) would be a worthy shot.

Sent via messenger pigeon - i talk, he types.

[packmule1911]

I used an adhesive wrap, then bent a shield and wrapped that as well.

That's some awesome work. I'm really hoping for something less involved though. The way it's going now, if I keeping "fixing" things, I'm going to continue breaking more stuff in the process.

[packmule1911]

I think replacing that shielding that is probably original with something new and possibly more effective (you would think they would have made advances since the millennium) would be a worthy shot.
I agree. I removed the old rotten insulation, and will look for something else more modern to use.

[Minihammermatt]

Hey I've had this issue before and I solved it by using DEI cool tube. I cover the fuel line from the rail all the way down the bottom of the firewallhttp://tapatalk.imageshack.com/v2/15/02/14/600ecd305c9c7896af0ec6265ba19374.jpg http://tapatalk.imageshack.com/v2/15/02/14/dbea3691e47c41ca652c48c7a1a006a0.jpg