2009 Vauxhall Tigra limp mode

2009 tigra with 47,000 miles , car has been going into limp mode for over 8 months , No mechanic seems to be able to fix it . It always shows a fault with the throttle peddle which has been changed 3 times now but still does the same . Plugs & points also changed & tried another ECU kit Current merchanic said there was water getting into the fuse box and there was corrosion. He cleaned it all and sealed the leak and said to see how that went but it is still doing the same , He now suggests replacing the fuse box but can’t guarantee this will solve the problem. I am reluctant to throw any more money at this , has anybody had similar problem or can help ? Management light off & on ,Thanks