Try typing 'dmesg' in the terminal and look for any timing problems or paste here if you can't read it. It's most likely a hardware problem assuming you didn't restore your settings and programs after flashing.

DSME handles the idle timer and I think there is a non-Nokia version you could try installing. Different software might fix the problem.

MCE sits on top of DSME and Powerlaunch has a replacement for that, so try it too.

Have you installed the community SSU and Diablo Turbo?

If none of the replacement software works around the problem then you'll have to do what tgalati4 said.