Ford Repair: 2000 Ranger misfire, couple seconds, cold start

Question
Hello,

I have a 2000 Ranger, V6, 4.0L, 4x4. 90,000 miles.

I am having a problem at startup, with a miss. It only lasts for a few seconds, then everything seems fine. It also only does it on a cold start, not when the engine is warm. Basically, it runs really rough for a couple seconds, the RPMs are low by a couple hundred, then it catches and runs fine. It does it 9 out of 10 times if it is cold. After it starts running normal, everything seems good on acceleration and higher speeds. If I give it any gas while it is running rough, it doesn't help, just starts bucking faster.

Last week I got a check engine light, and it came back as a miss in cylinder 4. There was no noticeable miss at the time, and it hasn't come back on since it was reset. I assume it is from the same problem.

I changed plugs and wires, which didn't help. The only other problem I had, was an issue with the IAC. Totally different problem, which was resolved by cleaning the IAC.

Any thoughts on what it could be? Could the IAC be acting up again and causing a different problem? I'm at a loss with it only happening at a cold start, and only lasting a few seconds. Thanks for any help.


Answer
Hello and thanks for the question...I'll try to help.
What I would suggest you do is take a look in to the fuel system...... if you are sure that the ignition system is not at fault. Maybe a clogged injector or a high resistance in the #4 injector which closes and runs fine when the engine is warmed up? I would also, suggest that you might have the engine hooked up to an ocilliscope and look at the firing pattern.
Hope this helps,
Erik