I've replaced my head gasket on my d16y8 engine. After connecting all the hoses, sensors, and wiring I noticed that while in park my revs go up and down between 1,500-2,000 rpms until the check engine light comes on. This only happens when the car is in park, while on drive the needle stays at 1,000 rpm without any acceleration.

Any idea why this is happening?

 

did you get any water into the maf sensor at any point? use a code reader my guess is your 02 sensor is bad.

 

Is the CEL ON? Have you checked carefully for intake air/vacuum leaks? Have you tried bleeding the cooling system and cleaning the IACV?

My guess is that you forgot to connect a vacuum line or the intake manifold or throttle body gasket is leaking.