2001 Hyundai Santa Fe Question: I'm getting an p1166 code but only when I've been driving over 50mph

I can drive around town and not get the CEL to turn on. If I do highway driving, the computer will throw a pd1166 and then on my next trip (the engine must be restarted) the CEL will light up with a p1166 and a pd1166. No other codes are popping up. Could this be the MAF, is there a way to test the MAF. The same code was being thrown when the crankshaft seal failed, but it would happen almost immediately.
Any ideas are greatly appreciated. Thanks Wayne