codes 46 and 51

Hey, maybe someone can help with some re-occuring codes I keep getting on my 94 firefly. I'll regularly get codes 46 and 51 together at the same time (always), and I can't seem to find the reason for it. I've completely re-done the EGR system, including clearing a nasty clog in the intake channel. I've followed the flowchart to try and diagnose the EGR, but with no luck. The VSV doesn't turn on at all, for reasons unknown, so I've bypassed it, but still get the codes. I'm fairly certain that the ISC motor is good still as well as the person I bought the car from had recently replaced it (trying to fix the code no doubt). What will cause the code 51? Any help is appreciated!