weird idle and p0101

just recently my monte carlo had a coolant leak at the lower intake gaskets. so i took it all apart replaced the upper, lower intake gaskets, thermostat and seal, and throttle body gasket. it no longer leaks. i then started it and i got the p0101 code which is the MAF sensor performance. also it started idling funny. when it is in park or neutral it starts idling at 2800 RPMs and raises to abouot 3500 RPMS. and then when it is in drive it has a constant idle at 1500 RPMs. could the MAF sensor being bad effect the idle like that. if not what is wrong with it. and on top of that there is a deafening screech that is really high pitched and i think that is coming from the alternator. can someone please help me with my car.

Welcome to AF. The screech is impossible to diagnosis from here. remove the belt and see what's what, also check the 2 seals under the map sensor make sure they are both there on the pcv and map. This can cause an vacuum leak that will set the code and can sound like a squeal.

the squeal is coming from the other side of the engine. around the alternator.

i am more worried about the idle and the code its throwing

i am more worried about the idle and the code its throwing

I would redo this job and find out what went wrong ...

It is most likely you damaged the maf sensor when you took off the throttle body. When your maf is bad your car will idle crazy and even shift different. Replace the sensor and you should be good to go.