With the car running, if you shake your wiring harness in the vicinity of the MAF, does the car stumble? I've seen a lot of 240sx's (both SOHC and DOHC) with bad wiring
Unplugging a vacuum line or 2 will get more air into the system that isn't metered, so that will lean it out.
Does it run rich while driving too? Or just at idle?