Here is the background information of this vehicle.
AC has worked forever, fine every time.
I noticed just recently that I need to keep moving for the AC to blow out
cold air. If I would sit in traffic for a minute, it will start to get hot and the car
temp will go over half...
If I turn AC off, the temp. returns to normal (a bit below half).

Recently it's been acting weird... I had the AC on and the car seems to idle
very roughly. If I am driving, I can feel a very slight 'pull' every second AS IF
I was turning the AC OFF and back ON again... (you know...that 'pull' and
extra 'power' you get by turning the AC OFF.)
The AC was on the entire time.
So I turned the AC OFF and it stopped doing this. Now it's just very subtle.
Once I had the AC ON at a light and it shifted very terribly. This happened
back in November once and never again. Now it's happening recently (last
week).

This morning, car ran beautifully. I turned the AC ON and it takes about 15
minutes to start being sluggish again. I turned it off and went home.
I looked it up and determined that the front condenser fan needs to be ON
when the AC is on... and it isn't... hence why I am overheating and my AC
stops working when I'm not moving.

I went to go for a drive and once I shift it into reverse, I hear a BANG! The
same for drive.
This is NOT the parking gear because I always put the emergency brake
on before putting it into PARK so that I don't rest the car on the parking
gear.

I let it sit for two hours and the same thing is happening.
This has not happened since November.
Does this have anything to do with the condenser fan?
The fan doesn't turn on - I suspect that's the issue with the AC and
overheating...
IDLE is fine.
Only when I'm driving with the AC ON does the RPM fluctuate when I'm
driving. It will go up to 2650 and then back down 2500. Then back up, etc.
Today, it did it with the AC OFF (after turning it OFF) but very subtle. You
can feel it very lightly.

So it's just strange that all of this is happening at once.
To learn about that fan cleared my problems... until I find out it's shifting
into PARK very bang-like.

Hopefully someone can figure it out and say something like - 'well this part
right here controls the fan and also tells the transmission when to shift'.
Then I'll be excited like when I figured out that the fan doesn't turn on and
why that's causing AC to stop and overheating.

I tried again and it's getting the same result. I scanned the codes and it found no logged fault code but it DID find a pending fault code. P0113. Intake Air Temperature Circuit High Input. The RPM started at about 1200 and then went down to over 500.

I checked the relay. Swapped it from heater/blower and the heater and blower still works but no fan movement. I'm not a Cavalier mechanic. I had when for a few months when I was 17, but then went to Mitsubishi. So I'm not familiar with this.

This transmission issue will only happen if I put it into reverse or drive. It doesn't happen if I put it into Neutral or Park. I read another post where it could be the TCC Solenoid IF it bucks in drive or reverse but not neutral, which is the case.

The only thing I changed was turning the heat selection mode to face so that the AC light doesn't turn on.
Car started fine, shifted fine, etc.
It shifts into second gear beautifully. I probably put it into 'drive' about 10 times without an issue. It always had a 'bang' when putting it into drive, but very subtle and not much of a notice.

Anyhow -- I am still wanting ideas on what else to check.

My Pontiac did the same my thermostat needed to be changed and change the coolant. My car would stutter and and with they Ac when I changed all that stuff the problem went away

I can't speak for the other issues but my 97 had that same bang problem when shifting from park to drive and such. Turns out it was the upper and lower motor mounts, the bang was the engine hitting the firewall due to bad mounts. Replaced them and no more banging.

Next time open the hood and have someone look to see of the engine is ramming the firewall when you shift. If so swap the mounts.

Intake Air Temperature Sensor
The Intake Air Temperature sensor measures the temperature of the air as it enters the engine's intake assembly. It is controls the air/fuel mixture within the engine, so as to provide the proper ratio required for the most efficient operation. It is also a component of the pressure control system for the automatic transmission. If it malfunctions or fails, the transmission may produce hard shifting or soft shifting, or produce a transmission fault code.

This will raise line pressure and give you harsh engagements.Let us know what you find.

"If you can't fix it with a hammer you have an electrical problem"
Brad
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