Nevermind about the firing order being different just check and the 4.0 and 4.6 have the same exact firing order

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A high idle could even cause a misfire. What rpm are you idling at. Maybe the IAC isn't adjust correctly.

 

Worth checking. Thanks.

 

welcome, my advice would be to see if your idle speed is at spec with the ac off. if so I would proceed to check the fuel injectors and the pcv valve. The pcv valve is located on the passenger side, some kind of tube that travels from the valve cover to the air intake plenum, just to make sure your not burning oil.

 

Is the IAC adjustable? 750 at idle.

 

Yes. It can be adjusted by the throttle body. Although iacs on newer cars don't need to be adjusted since they are electronic. 750 Rpms sounds about right though. You could probably eliminate a high idle out of the equation now.

 

Right, no adjustment on the D2. Some folks do remove and clean inside. Plan to do a clean/light lube on mine in the future. 750 is just a bit above 660 ± 50 rev/min spec.
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Good plan. Hopefully your issue was a high idle. I wish you the best of luck then.

 

After all you have done I would focus on the number 4 injector. Aside from it being clogged and not spraying properly, the injectors have an o ring on the top and bottom that will degrade with time and allow a vacuum leak. Also, when the injectors are replaced, you have to put some lubricant on those o rings to keep them from being torn because the fittings are very tight. I had a mystery misfire and that was the cause.

Next time you have the upper intake off you should swap the 4 and 6 injectors and see of the misfire follows. If it does, you'll have the solution. Just he sure to use a small amount of Vaseline when you press the injectors in or you'll end up with more misfires. And if any of the o rings look bad, they are super easy and cheap to replace.

 

I will be checking the injector next time its apart, for now i guess i should check the vaccume lines. Thanks .