I've had this same problem on my '02. It only runs rough on cold start-up when the outside temperature is below about 50 degrees. I've had it to the dealer several times, been on the phone with Dearborn, and no success.
FauX, I'm running 5w30 synthetic blend. Do you mean to say that Fletch's problem has to do with the oil?
I thought about MAF, IAC, and the TPS. The dealer says they're all within range, but I know there can still be a problem. I hate to throw parts at the truck until I find a fix.
Fletch, you had any luck in finding the problem?
2003 Ford Ranger | FX4 Level II | 5-Speed Manual
A few minor mods... nothing cool enough to mention.