'00 XJ 4.0L - First start when cold problem ---- Please Read..

Hi All,

'00 Cherokee XJ with 4.0L, 48k miles. Runs perfectly in every way EXCEPT: cold starts will result in about 10 seconds of roughness, enough to cause a little bit of wobble to the body.. It runs rough about long enough after starting to: put on the seatbelt, check behind me in the mirror and adjust the radio.. After that it is butter smooth.

Oil pressure runs about 50 at highway speeds about 20 at idle.

Runs great other than this. Warm starts (even after a couple of hours while the internal engine is warm are fine --)

Any ideas? I'm new to Jeep.

Thanks in advance

Marc

Reply to
Marc
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Marc did pass the time by typing:

First off, are you under the 7-70 powertrain warantee? If so, take it to the dealer.

The primary cause of a rough idle is a clogged IAP (Idle Air Passage) or gunk in the throttle body.

look here.

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It could also be a sensor reading poorly, but before we go there check/clean the throttle body.

Reply to
DougW

Doug,

Is it best to remove the TB to clean this, or can it be d> Marc did pass the time by typing:

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Marc

Reply to
L.W.(ßill)

Yes, forgot to include that, changed the plugs.. It doesn't cause extended cranking times or anything, just a fairly rough idle for about

10 seconds then she's fine. No smoke (blue white or black) from the tailpipe either..) Cleaned the TB. After that first 10 seconds it pretty well idles butter-smooth. Power and response are great on the road too.

Reply to
Marc

Marc did pass the time by typing:

It's easier to just spray the slot. That TB was off since it was replaced with a larger bore when I supercharged. (it's sitting in the garage and still dirty) :)

You can remove it though. You can also pull the IAC solenoid off, but usually spraying with the engine running is enough. Then use a paper towel with cleaner and wipe under the butterfly. (an old toothbrush also works well)

If you pull the TB, remember those screws holding it down only get torqued to 32 in.lbs (that's inch lbs) (2.6 ft.lbs) You can put way more than that on with just a nut driver. finger tight + 1/4 turn is a "close" estimate.

Reply to
DougW

Ok, just got back in from spraying down that slot, wiped down.. I did call the local jeep dealer and there is an issue "rough idle at cold start" that is addressed in a PCM update. I'm hoping that this might be it, or spraying down that slot. FWIW, that TB was pretty dirty yesterday when I took the small brush to it; now it's almost shiny.

The dealer mentioned about carbon buildup on the back of the valves; that it might be absorbing the first few moments of fuel sprayed in. . I think that if the first squirts of fuel were getting absorbed by the carbon that I'd get extended cranking time most likely..? He mentioned to use some chevron techron concentrate in a full tank and see if that helps, which I have some of that already waiting to use actually.

Marc

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Marc

Marc did pass the time by typing:

Did this just happen after your last tank of gas or has it been going on longer. Might try adding a bottle of fuel injector cleaner with water disperser (gunk or valvoline) with the next fillup, and try a different station.

Other causes are sensors or vac leaks that seal with expansion, the warmup loop is fairly forgiving and bad sensors will cause rough idle even after warmup.

Start the motor and spray some TB cleaner around the base of the TB. listen for any RPM change.

Reply to
DougW

Marc did pass the time by typing:

Gets nasty doesn't it. Go for the PCM update it might be a programming problem. If it was real nasty you might benefit from removing the IAC (four antitamper torx screws) And cleaning the guts.

Before you do that, disconnect the hearness from the TB (IAC and TPS) then reconnect. They might be a bit corroded. Every once in a while I disconnect, clean, and apply some dilectric grease to the sensor connectors.

Yep. Generally the fuel is atomized by the injectors before it even gets to the valve. A dripping injector will cause buildup but it will also cause a hellaciously rough idle.

See my other post. Doing that every year is a good thing. When you use a fuel injector cleaner read to make sure it is safe for O2 and catalytic converters. Also look for one that says to use it every 3000 miles or so. The ones for use with every tank are generally too weak to clean anything.

Reply to
DougW

Carbon deposits on the back side of the intake valves will cause this concern, and Techron will likely eliminate it. Very good product, does what it says it will.

GM has a little trouble with cold misfires in some engine families. Engineering has traced the cause to these deposits. They put out a bulletin and actually recommended Techron by name. I have found that it fixes these sorts of problems nearly 100% of the time.

The deposits we are talking about are like a sponge. Atomized fuel flows past the top of the valve and into the cylinder, but this sponge-action actually absorbs a miniscule amount of the fuel on cold start, causing lean misfire. Once the sponge becomes saturated with fuel, the misfire disappears.

Jerry

Reply to
Jerry Newton

In article ,

Sounds like a plan.. I have a Haynes manual and what I'd consider a pretty good understanding of under the hood (thanks Dad). Have the appt. for next Thursday for that PCM flash.

Check. I'll get that tomorrow too.

Idle is butter smooth after about 10 seconds. The engine always lights up within 2 seconds of turning the key, hot or cold.

Yup, every 3000 right on the bottle. I will change the oil in about

400 miles, so I'll dump that in the fuel on Monday.

I'll check those connections and all this weekend and report back.

thanks!

Marc

Reply to
Marc

It's been since I got it, about 10 days ago, but it was going on most likely before that. When I test drove it someone else had just come back with it, so I got it with a warm engine. Otherwise cosmetically it is perfect and after that cold start it runs beautifully.

Just rather disconcerting to get an initial idle rough enough to jostle the vehicle for a number of seconds till it levels out..

I'll check your other suggestions this weekend and report back..

thanks Marc

Reply to
Marc

I have a bottle of techron concentrate (up to 20 gallons treatment), that I picked up at Target for $4.84 (on clearance I think), so I plan to load up the tank this weekend with it.

Hoping that between the techron and the pcm update, one of them will get it. What kind of time frame would I be looking at to see if the techron is making a difference? The whole tank run through, 100 miles, etc?

Marc

Reply to
Marc

EXCEPT: cold starts will result in about 10 seconds of roughness

Reply to
Rob Mills

Rob Mills did pass the time by typing:

The "clock spring" is actually a spiral of flat wires that winds around the steering shaft and connects the electrics to your horn, cruise control, and airbag.

Reply to
DougW

Reply to
mic canic

Well, no leaks around the base of the TB, sprayed that slot out really well, but still no dice. I'm getting a full tank today and will put that techron concentrate in. I do have that appt on Thursday for the PCM update about rough idle upon cold start.

Not giving up yet :)

thanks

Reply to
Marc

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