Code 51

I've had a code 51 on my 1994 Firefly for a while but can't get rid of it. I changed the EGR valve (it was rusted), checked all hoses and even tried another Map sensor.
By the way, the car works perfectly well. Any ideas?

I can't wait to get rid of that annoying "check engine" light.

Have you reset the ECM to get rid of old codes, to insure the check engine light is reporting a current fault?

Yes I did, by removing the tail light fuse. The Check engine light comes back on after 16 km to 20 km.

I finally found the problem. If you have the same code 51, replace the hose with the white filter (I think it's a filter) that goes from the MAP sensor to the throttle body. I got one for free at a local junk yard.