Fuel injected Prelude Si My intake manifold gasket was blown out. This caused massive vacume leak in the intake causing idle to surge from 1200 - 2500 RPM. Other weird associated symptom - while coasting above 30 MPH, idle would remain high at about 3500 - 4000 RPM. When coasting slower than 30 MPH, idlle resumed surging 1200 - 2500 RPM. Replaced the gasket and the car runs like a champ. BTW, I took out the whole EFI manifold assembly so I could clean away all the old gasket material. It was a PITA.
