Question: My 2001 Dodge Ram 1500 5.9 gas engine stumbles and backfires when cold. After short warm up seems ok. Any suggestions? 180,000 KM.

Answer: Two possibilities come to mind…

1. Faulty coolant temperature sensor could be causing the ECU to
think the engine is warmer than it is, thus not enriching the air/fuel
mixture. This usually trips a check engine light though.

2. Dirty throttle body could cause issues like this as well. You can
clean with throttle body cleaner, making sure to get the IAC (Idle Air
Contoller)

Since its easier to tackle, go to your local auto parts store and get
a can of throttle body cleaner. Take off the air intake hose, and
spray everything inside. You may also want to check out
http://dodgeforum.com/forum/dodge-ram-van/68174-diy-how-to-clean-the-iac.html
for free instructions.

If cleaning the throttle body does not help, I would then check out
the temperature sensor by hooking the ECU up to a scan tool and see
what the temperature reading is at start up, to see if its accurate.
Most auto parts stores will allow you to borrow a scan tool, but if
you cant find one, you may have to go to a mechanic to have this step
done.