Rough idle at start, then runs smooth

[willfargo]

96 4.0 vin x
Every time I start it, it runs really rough and wants to stall. As soon as I drive it down the street, it idles fine and runs great. Even if I shut it off and start it up right away, it runs rough again.
Not throwing any codes to help me with.
Trying to pinpoint what could be causing it. I was thinking maybe coolant temp sensor, but the gauge works.
Hoping it's not the IAC, those look pretty pricey.
Maybe IAT?
Any thoughts?
Thanks

 

[J_C]

IAC is only $50 or so at Rock Auto and is a prime suspect if it only runs rough at idle, though you can try cleaning it out, which may help even if only in the short term. AFAIK the Hitachi on RA is the OEM part so there is no reason to pay double for the Motorcraft relabeling of that same part.

1996 FORD EXPLORER 4.0L V6 Idle Air Control (IAC) Valve | RockAuto

It is more a matter of doing it idling or more a matter of how long it's been running? Does it get better if you just leave it sitting idling for a minute?

I'd hook up a scan tool capable of live data and look for misfires, fuel trims, and temperature. I'd also check the battery voltage in case it's getting weak spark and along those lines, consider how long it's been since the plugs and wires were replaced.

 

[slisman]

You can also check your fuel pressure - it's easy and free There is a shrader valve on the fuel rail, just plug clock and check how pressure behaves. I had similar issues with broken pump - idle was rough, then I could shut it off and idle again - it was good then. Performance under load was poor of course - but it was only noticable after pedal to metal.

 

[96eb96]

96 4.0 vin x
Every time I start it, it runs really rough and wants to stall. As soon as I drive it down the street, it idles fine and runs great. Even if I shut it off and start it up right away, it runs rough again.
Not throwing any codes to help me with.
Trying to pinpoint what could be causing it. I was thinking maybe coolant temp sensor, but the gauge works.
Hoping it's not the IAC, those look pretty pricey.
Maybe IAT?
Any thoughts?
Thanks

Lots of little things could cause this-
vacuum leak
dirty/failing IAC
dirty maf
fuel pressure

BTW- the dash has its own "private" temp gauge. The PCM has its own.

Can you use a scan tool to get fuel trims at idle?

 

[willfargo]

Well this is embarassing...
I KNEW I could hear a vacuum leak so I kept investigating that. Couldn't find it, so I finally broke down and paid for a diagnoses.
Turns out the EGR Tube was slightly bent out of place, and the rubber seal around the tube leading in to the intake was old and loosey goosey.
New EGR assembly is on it's way.
SOOO annoyed I couldn't tell where that hissing was coming from. I couldn't keep it running long enough to really investigate

 

[EB4X]

I'm surprised it would run fine later and only do at startup... research here for headache removing/ reinstalling EGR assembly/rubber seal.
Stuck - Remove EGR Tube to Remove Upper Intake
I just did my upper intake gasket etc and got my egr tube to pop out during removal but seal got jacked up during assembly (probably my-bad, wrong approach etc) but anyway instead of going through 'said headache' on link....I just put a thick bead of Permatex high temp around fitting....done....leak gone....don't usually mickey-mouse things but to avoid that headache worth it to me.
https://www.walmart.com/ip/Permatex...MIr4n_2vuu5wIVyrzACh23qQEREAQYASABEgKpw_D_BwE

 

[willfargo]

Well that certainly would have been much cheaper than $80 for new tubes... but mine had obviously gotten bent at some point, if it was mounted to the header stud, it would pull out of the intake meaning it obviously had gotten damaged somewhere between installing a new engine and replacing the intake manifold gasket. Sloppy work on my part

 

[slisman]

Please update after installing new tubes. I am curious if it will help for your symptoms.

 

[willfargo]

New tubes solved the issue. The rubber on the old one was certainly worn and very very loose.
Runs like a champ now.
Only issue is it has choked out on me and couple of times when it sits overnight in the cold

 

[slisman]

Great news!

And old tubes looked bad? Have you any photo?