If your turbo bypass valve is bad the turbo will overpressurize the intake system after you let up on the gas. This extra pressure pushes oil vapor into the IAC and gradually gums up the brushes. It eventually starts coming out of the IAC plug socket. You can check the bypass valve by pushing the diaphram in and plugging the vacuum line with your finger. If the diaphram valve springs back all the way when released then it's bad. Unfortuately I've never seen them for sale seperately. The IAC can be checked by connecting the battery ground to the center pin and applying 12 volts to the side pins one at a time. The valve should quickly flip back and forth. Lots of carb or brake cleaner with clean the valve mechanism. It should flop back and forth when you flip the valve around. But you really have to test it to be sure it's working properly. Your throttle isn't sticking open is it? Some signal is telling your injectors to squirt more fuel. Maybe you throttle position switch needs adjustment?