Check engine light on - only during acceleration

Hey all,

My brother is having a problem on his 93 5.0 5spd Mustang. Under acceleration he says he's getting some knocking and the check engine light will come on. Once he gets off the gas, the light goes off but will come on again when he accelerates. We haven't done any diagnostics yet....but does anyone have experience with this problem and know which sensor(s) may be affecting the performance? We're thinking maybe the mass air or maybe O2 but aren't sure yet.

The car has been sitting for about a month, so that may have something to do with it. He says he plans on a 50 mile or more run to get things nice and hot to see if that changes anything.

Thanks for the responses....

check your anti knock sensor

Makes sense. I passed along the info and he likely knows, but where is it located?

Sounds like the EGR system is faulty. Hve the codes checked.

He's got it fixed now, you were both right. Appreciate it.