[jpnovak]

Usually a suddenly rich is due to a failing sensor. This would be for all EFI types. Here are the most common.

Check the MAP sensor lines to make sure the are not cracked or pinched. This will tell the engine it is running WOT all the time.

Check the Temperature sensors (you might have two). Failed open (high resistance) typically means the engine is cold and enrich the mixture

Check for reference voltage at the TPS. No reference voltage usually means the TPS thinks it is WOT and will enrich to compensate.

Do you have a PC interface? This is the fastest way to look at these values.

BTW, any Motec tuner/operator should be able to plug in and diagnose very quickly.