Rent a steam cleaner for the engine bay if you have the time to mess around a little. I did this with a friends car. The other option was to buy a case of brake cleaner and goto town scrubbing. We decided on the steam cleaner so we could hit the rear of the car aswell. It was amazing how much crud accumulates on the transmission and rear suspension. We got a little carried away and did the wheel well's also. Who would have known the undercoat is the same color as the car...and not black
. It also did a great job cleaning the metal heat shields and insulation around the firewall.