David, You said: "A noisy mode switch can be a major vacuum leak." A defective mode switch may leak vacuum, but not enough to drastically effect engine operation. DMC Joe "We're here to help you" DMC Help / De Lorean Services / <dmchelp@xxxx> Web Site: <http://www.deloreanservices.com"> DeLorean services.com DMC.tv is in your future ..... to the modulater! A noisy mode switch can be a major vacuum leak. Also make sure that the idle motor is controlling the idle, you can test this by pulling off the plug to the idle