I was getting MAF codes and did a bunch of things (smoke test, swapped good MAF in, etc) with no luck. Finally removing and cleaning gummed up throttle body solved problem. My theory is throttle was sticking and not closing fully (I could see abrasions on throttle body where plate was dragging on build up). As a result MAF readings didn't correspond to throttle command. Hence the MAF codes, even though it was reading correctly. I removed manifold to do throttle cleaning, and also threw in an IPD phenolic throttle body spacer as thermal break to protect throttle body while I was at it.