A code 42 is the hardest OBD-I code to properly diagnose. Most times it is caused by a bad CKPS (CranK Position Sensor) and/or the wiring to it, or a bad ECM. DIY tests include the ECM "tap test" which consists of lightly tapping on the ECM case (preferably with the plastic handle of a screwdriver, nothing metal) while the car is running. If the car stumbles or dies, the ECM is a likely cause. The other is a visual check of the wiring that goes from the CKPS to the ICM. It goes from the back of the block, under the harmonic balancer, and across the front of the block to the ICM. On it's way, it runs very near many moving (RF CV axle, harmonic balancer,) and hot (both exhaust manifolds) parts and can be chaffed or burnt or damaged by road debris if it came loose from it's factory restraints and is hanging down.