I have a 2012 5.0 STX 4x4 with 400 miles on it and when I start it up ( cold start ) it starts just fine but after it starts for mabye 10 seconds or so the rpm's vary mabye 100 up and down then it smooths out not to worried but is this normal?

 

For the first 10-20 seconds or so on a cold start, most any OBD2 gas engine will be that way until the heated oxygen sensor warms up to operating temp so it can function. Until that happens, the engine is running in a bypass mode of sorts, open/closed loop.

 

Dad's Limited does that. You can feel it when slowly moving after a cold start. My Eco is smooth as silk when starting. Maybe just a V8 thing? All them big man cylinders warmin up?

Our Escalade does it as well.

 

My 2011 5.0 4x4 varys -+ 50 on could start but fine once warned up. Every ford I've seen does that. Truck runs great and love it.

 

Not to worry. The Wifey's 5.0 Mustang does the same. Smooths out nicely very soon.

 

thanks for the feedback guys just wanted to make sure it wasnt a fault on my truck

 

My 3.7 does this as well, so it's not just limited to the 5.0.