Troubleshooting a Cold Engine Stall After Start

[mu2bdriver]

For about a month my wife has been having cold engine starting trouble in her 2004 3.7. Warm-engine starts are unaffected and the only way to keep the vehicle running when cold is to apply enough accelerator to maintain about 1000RPM until the vehicle can idle on it's own.

Air filter was replaced.
Airbox was unobstructed.
Fuel treatment (STP) has been run every few thousand miles since new,
New OEM spark plugs,
New idle air control valve.
Vacuum lines appear good.
No codes, no CEL.

After start the RPMs will just smoothly drop to zero nearly instantaneously after the key recoils to the run position.
If I open the airbox clips and open the top part a little you can hear a sucking sound like I just released a vacuum.
I'm about to go clean the throttle body of any carbon buildup but was curious if anyone else had other ideas.

Thanks in advance!

ETA: Just finished cleaning the throttle body and there was some carbon buildup, nothing awe-inspiring, but it's cleaned out nonetheless. Will report back after sitting out overnight.

 

[LibertyTC]

I am wondering if the fuel pump or filter may be suspect?
Get fuel pressure reading..I think it should be 44-55 psi...
http://www.jeepkj.com/forum/f202/how-change-fuel-filter-27498/

 

[mu2bdriver]

I am wondering if the fuel pump or filter may be suspect?

That's what I thought at first but when you turn the key to acc I can hear the pump, it doesn't sound rough or nasty, and there are no harsh vibrations on the tank. If it were a bad pump I would expect the engine to be rough throughout the entire spectrum of operations, and not just the start. I couldn't believe that there isn't an external fuel filter.

After cleaning yesterday, I let it sit for ~7 hours, re-started, and it started fine. Let it sit overnight for about ~12 hours in 15 degree temps and it fired right up this morning. Based upon how much carbon gunk I pulled from the throttle body I would not have thought it would make much of a difference, but I guess it did.

The wife is happy but I'll reserve judgment until it starts and runs fine for a week without any issues.

 

[LibertyTC]

Yes the throttle body can build up carbon & intake air dirt pretty quick, especially if lots of city driving & never cleaned before.
I am sure if u replaced the IAC and sprayed out the port it gave u an indication of what was going on in there..YUK!
I remember a while ago the butterfly or throttle plate was sticking a bit at idle givin me a higher than normal idle, it was so bad.
What I found was that on the top and bottom/side edges around the plate it was built up badly. I ended up using some q-tips soaked with Spray carb cleaner (only on plate) edge surfaces. while throttle was opened a bit, (not running) to get it clean again. And then applied a small bit of wd-40 on edges to ensure free movement and to not have it stick at all. The tolerances around the plate are tight indeed, almost too tight. For regular spray inside the throttle body I use a MAF sensor friendly Throttle body cleaner in a light application, just to clean the round interior of body and get er shiny again.
I think I am due for a 2 hr+ highway blow out soon & for injectors, I use 2 bottles Chevron Techron concentrate in the fuel tank. Link:Chevron Techron Concentrate Plus, 10 oz: Motor Oil, Transmission Fluid & Car Lubricant : Walmart.com
Many also use Seafoam engine treatment as well.Link:Sea Foam Motor Treatment - Sea Foam Sales Company
Let us know if the Jeep runs without stalling in a week or so. Hopefully it was just the TB that needed attention!

 

[mu2bdriver]

Will do! Thanks again!

 

[mu2bdriver]

It's been a week and about 4 cycles/day without any stalling/starting problems. I'm hoping the problem has been solved.