'98 Ford Explorer rough cold start

Any help?
My 98 Explorer has been a rough start for more months than I can count now. On the rare occasion that the "Engine" light comes on, the code has
indicated a lean let bank. Garage mechanic (none Ford dealer) thought it might be a cracked intake manifold that, after warming for about 5 minutes, expanded and sealed itself. Mechanic chased cracked manifold with no results.If car is started for 1st time after sitting in very warm ambient temps (>80) or in the sun, no prob with rought start.
Anyone out there with any ideas?
Thanx -- Jim P.
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Have you tested your O2 sensors? The age of the vehicle seems about right for them to be failing...
-JCM900

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JCM900 opined in

Bullshit!
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Backyard Mechanic opined in

Sorry 'bout that....I must'a thought we were a bunch of guys sitting at the bar.
What I REALLY should have responded is:
"I dont think so, Tim!"
While I would think a bad oxygen sensor might maybe cause that, possibly in a rare case, someday, somewhere... it's WAY down the list.
The engine STARTS with the O2 sensors not in the loop. The ECM logic runs from a map set when in full warmed up mode. An old sensor just switches slower, allowing a wider swing in mixture. Unless the sensor isnt switching at all, it's still setting about the same average injector dose. If there's no code saying it isnt switching, then it's hardly the problem
Actually the tech's idea made a lot of sense. It is likely a variable or intermittent vacuum leak. Check for cracked vacuum tubing tees and connectors... that Is a common problem
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