2000 4.0 SOHC Dies Once During Warmup

[Ben1]

I've got a 2000 Explorer with the 4.0 SOHC. Runs fine except during warmup when it's cold (less than about 40). I start it and it idles fine for about a minute, then the rpms start to drop and it dies. If I restart it, it restarts right away and idles fine after that. When I initially start it, if I rev it up just a couple hundred rpm's for a second or two, it will continue to warm up and won't die. Or if I just start it and take off, it runs fine. So it's only when I initially start it and don't do anything; just let it idle and it dies after a minute or so.

I've checked the IAC valve, looks clean, seems to move fine, and passes the resistance tests my chiltons manual indicates to do. Plugs and wire are fresh. No check engine light. Definitely seems like an electrical/sensor thing going wrong during the warmup cycle but I don't know what would be the next thing to check. Any ideas?

 

[koda2000]

Intake manifold O-rings?

 

[Ben1]

Did some reading on that. Looks like an afternoon job, so I'll have to think about it. Runs fine otherwise, so I'm not sure right now it would be worth doing yet.

 

[koda2000]

Did some reading on that. Looks like an afternoon job, so I'll have to think about it. Runs fine otherwise, so I'm not sure right now it would be worth doing yet.

It's not running fine. It stalls when first started. This (and/or a rough idle when cold) is a classic symptom of dried up, stiff, leaking intake manifold O-rings. Eventually it will leak enough that you'll see the CEL come on with P0171/P0174 codes.

As then engine warms up parts expand and the O-rings may get sucked down, temporarily stopping the air leak.

 

[wcjeep]

The intake Orings are not difficult. Pay attention to proper torque specs on the intake bolts. I followed the book which was wrong. Snapped a bolt. Then had to find one late on a Saturday.

 

[Ben1]

Replaced the upper and lower gaskets and it's still having the same problem. Everything looked fine and I followed the torque specs. While I was doing that, I looked around for any vacuum leaks I could find and didn't see anything obviously broken or loose. Don't hear anything when it's running either. Any other typical suspects in this scenario?