intake manifold vs MAP sensor

I'm getting a code 33 - MAP sensor. My question is, can a leak at the intake manifold be the cause of this due to vacuum leak or something? I don't want to replace the MAP sensor if it's working correctly, and the problem can be solved by replacing the intake manifold. BTW, I've been told the intake manifold does need to be replaced.
Also, can this be what's leading to my erratic idle when I put the car in park? After a good drive, when I put the car in Park, the rpms will shoot up to around 2000. This used to be solved by applying pressure to the brake pedal, but this isn't working anymore.

1989 uses a MAF sensor, not a MAP sensor. Code 33 is MAF voltage low. Replace the MAF power relay and MAF burnoff relay, located on the driver side firewall and they cost around $17 each. The idle doing what you describe would be a good indication of a vacuum leak, either the manifold gaskets or vacuum hoses or the rubber boot not being on the throttle body tightly or correctly.

Thanks for that solid advice. The boot on the throttle body actually does have a small piece broken off of the clamping area. I didn't think of that. Very cool, man.

Thanks for that solid advice. The boot on the throttle body actually does have a small piece broken off of the clamping area. I didn't think of that. Very cool, man.
Also look at the bottom side of the boot for a hole where the coolant bypass hose rubs.