Inconsistent idle missfire-2003 trac

[Nctruckman]

Having an inconsistent miss fire only at idle. 2003 4.0 with 283k
Heads, chains and guides were redone within the last 80k miles
Taylor plug wires, new motorcraft plugs 10k ago.
New ford IAC
Only thing I've found is a mode 06 value that's exceeding the limit.
No errors or codes showing up.
Trying to keep this old thing running perfect, but I'm not sure where to look.
Does anyone have something to decode these numbers?

 

[410Fortune]

With 283k miles I start to suspect a fuel injector or two maybe failing? Have you ever replaced your intake o rings? Maybe a good time to check on the injector o rings and plastic seats they sit in

 

[Nctruckman]

Later last year I suspected that, replaced the intake gaskets( they were done as part of the timing/ head work in 2019). I replaced the injectors seats, the injector screens, the tips and the orings. Bench tested them with a tester, all seemed consistent. I really don't know what to check next. Could be a vacuum leak, but I replaced the Pcv valve and elbows when I did the intake gasket/ injectors

 

[oklagp1200r]

Later last year I suspected that, replaced the intake gaskets( they were done as part of the timing/ head work in 2019). I replaced the injectors seats, the injector screens, the tips and the orings. Bench tested them with a tester, all seemed consistent. I really don't know what to check next. Could be a vacuum leak, but I replaced the Pcv valve and elbows when I did the intake gasket/ injectors

Have you ran any Tectron fuel treatment in your gas?
When was the last time the fuel filter was changed?

 

[MakinJeepsWeep!]

Tried resetting the tps and your manual throttle stop? After all those miles stuff might be getting slack and wear.

 

[Nctruckman]

Have you ran any Tectron fuel treatment in your gas?
When was the last time the fuel filter was changed?

I haven't ran techron, there's a high strength berrymans treatment I have used. And it was changed within the last 10k miles, earlier this year.

 

[Nctruckman]

Tried resetting the tps and your manual throttle stop? After all those miles stuff might be getting slack and wear.

I replaced the TPS with a new ford one last year. I think the pcm sets the idle speed with the IAC. I couldn't get it to replicate the issue today, drove 30 miles.

 

[MakinJeepsWeep!]

It doss set it that way, however first you unhook iac and set throttle plate stop to where motor will just barely stay running then shut off motor key on and probe your tps wires black and green if memory serves and set to .07 .08 volts. Then unhook battery to rest memory or use scanner. Hook iac back up and your done. I'm just wondering if plate has moved far enough iac has run out of room to adjust further to raise rpm and your catching a stumble here and there. Just a possibility.

 

[Nctruckman]

It doss set it that way, however first you unhook iac and set throttle plate stop to where motor will just barely stay running then shut off motor key on and probe your tps wires black and green if memory serves and set to .07 .08 volts. Then unhook battery to rest memory or use scanner. Hook iac back up and your done. I'm just wondering if plate has moved far enough iac has run out of room to adjust further to raise rpm and your catching a stumble here and there. Just a possibility.

Is this the same procedure streetrod2000 has on here? Wasn't sure what years it pertained to.

 

[410Fortune]

Misfire generally in the injectors or ignition
Pull plug from effected cylinder and have a look at the tip

Check ignition wires
Check coil
Pack, they like to crack on the underside when they fail

 

[MakinJeepsWeep!]

410 is right if you can pull your plugs and find the one that's off compared to the others that is your problem cylinder.

 

[410Fortune]

Inconsistent misfire at idle

If it is a Misfire it is happening all the time it is just more apparent at idle

Check your work it could be a plug is bad or a plug is not fully seated or a wire melted or??

 

[Nctruckman]

If the thing would do it more often I could do that, but I'm starting to wonder if the base idle procedure and the reset would resolve it. Ran fine this morning to work with no missfires registered or felt.
Throttle body has been changed and it has a sct tune.

 

[Nctruckman]

Did the base idle adjustment. Definitely was out of whack. Idle speed with IAC unplugged was over 600, adjusted it to 500, reset it, drove it, no rough idle, seemed to adjust to loads like ps steering pump/ ac compressor much much better.
Before It was set where it'd bog the engine so much the oil pressure gauge would flutter, thinking it was a ps rack issue.

From what I gather the throttle screw was set in too far, so the IAC wasn't in the range where it could compensate well under load at idle.

I have noticed on some gen 1 Tracs, they don't have a screw, it's a smooth pin that you can't turn like some .

 

[MakinJeepsWeep!]

Glad to hear it helped.