5.7 Vortec Surges When Cranked

[cris well]

When I first crank it up it surges to 1500 RPMs for about 10 seconds then drops back down to around 750 RPMs which is normally where it stays.

Has anyone had the same problem?

[400sbctruck]

Does it do this mostly from cold start or all the time?

[cris well]

It just started doing it today.

The first time I cranked it didn't do it but every time afterwards it did it.

I will try it again tomorrow and see. I unplugged a couple of the sensors in the air intake and plugged them right back up to see if maybe one was stuck or something but it still did it.

[400sbctruck]

If it is ran until operating temperature is reached, and shut off? Does the symptom still appear if you shut it down and restart?

Idle control never moves without reason, coolant temp sensor dumping fuel and takes a minute for o2 sensor to pick up rich would give that exact problem. If warming it up and retrying seems to help, throw a temp sensor at it, ASSUMING the o2 isnt reading roughly/poorly due to ethanol, age, etc.

Buildup on o2 adds latency and inaccuracy to the equation, and wont necessarily trigger engine light until it reads outside of parameters.