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Cold Start problem

OldTech

New Member
Joined
November 19, 2019
Messages
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City, State
WillowSprings Mo
Year, Model & Trim Level
1994 Explorer XLT
My 94 Explorer has a problem with cold start more so in cold temp, surges and irratic idle till engine reaches operating temp then runs fine. Has had fuel pump replaced fuel filter, Iac Motor, IAT sensor, upper and lower intake gaskets, MAF cleaned, both 02 sensors, no CEL coming on. Only has 107,000 .miles engine looked new inside, has been well maintained , idles please.
 



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Temp sensor. One is for the gauge, One is for the PCM.

Or you have a vacuum leak that seals up when heat causes things to expand.
 






Temp sensor. One is for the gauge, One is for the PCM.

Or you have a vacuum leak that seals up when heat causes things to expand.
I replaced upper and lower intake gaskets last week, still same issue, finding no vac leaks anywhere, need to find location for coolant temp sensor for PCM, runs great after warmed up. This 94 only has 107,000 miles been very well maintained before I bought it.
 






The sensor with the single pin on the lower intake to the left of the thermostat housing is the gauge, there is a two pin on the opposite side of the housing, that is the one for the PCM.
 






Found it and replaced it will now see what happens in the morning when cold outside.
 






Disconnect battery to reset the PCM
 






Seems like if not one thing its something else. The ECT sensor helped a lot, but now back to the problem of popping back thru the intake at idle. I recently replaced upper and lower intake gaskets, the IAC , IAT sensor, fuel pump and filter new spark plugs and wires, both 02 sensors, still has no check engine light coming on, have reset PCM, what am I missing?
 






Timing chain may have jumped a tooth or two.

Time to have a look at the mechanical timing.
 






Double check the plug wires and firing order. Ignition timing is off the crank and without shearing the key holding the Harmonic Balancer is almost impossible to break mechanically.
 






Sorry, about the "disagree." @OldTech . I think I was on my phone and hit the rating icon by mistake.
 






This only happens when cold, after it warms to normal temperature it runs fine. It idles so smooth when warm at times I look at the tach to see if its running . The idle surges and pops thru intake to air filter housing. I've seen this posted a bunch just haven't seen where anyone has figured it out.
 






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