Need Help Fast CEL on&off

[slow16G]

I am putting my car back to stock. In the mean time I put the stock mas air on. I rebuilt the throttle body this past winter and now I have the car running, it starts fine, slight miss at idle, and when its idling the check engine light will come on. It only does this after it has been idling for 30seconds. As soon as I barely touch the gas the check engine light will go out, as soon as the light goes out, I let it go back down to idle and it comes back on. I know it has to be a sensor but which one? I need to know what this is, I am trading the car on Saturday and hope someone can help. Thanks Guys

 

[SchmeelDeal]

Could be your engine coolant temperature sensor. It's on the thermostat housing. When mine went out, it acted funny like that going on and off. When it went out totally, after about 30 seconds of idling, the CEL would come on and stay on. At that point, I was getting a code 21. I picked one up for $30 at Advance and the CEL went out.