First Start Up Backfiring

[1BadBowtie]

I just did my first start up last weekend. It starts up just fine after I had an initial issue with the starter. I only have the long tube headers on it at this point. Everytime I start it it runs for a few seconds at 1000 RPM and then starts climbing from there without me touching the throttle. During this time it will backfire. I have checked the wiring and spark on all of the coils. I don't know what it could be.

 

[DerekTheGreat]

Year and engine would be helpful here, your sig suggests it might have an LS of some sort in it at this point..

 

[1BadBowtie]

Yah sorry, The truck is a 98 k1500 and the motor is a 2005 6.0L LQ9

 

[1BadBowtie]

UPDATE: No more back firing. I did a spark test and all coils are firing, put it back together and the motor runs without any misfires. I now have an issue that the motor starts up, runs up to 2500 then 3500 and doesn't come down. Im thinking it might be the IAC but not sure. The motor is drive by cable.