1989 240DL On a trip this weekend the idle speed began to increase. An hour into the trip home the idle would race up and down. Cleaned mechanism in valve. Tested to battery. Snaps back and forth. Car still revs up and down. Disconnected both in and out hoses and blew in. No air leaks. With engine running and control valve intake hose disconnected and plugged car idles fine, and when the engine speed in increased/decreased the vacuum in the intake decreased/increased. (Slow idle, increased vacuum.) The valve mechanism seems to be functioning correctly. How can I tell if it is the computer? What else do I want to check? When the valve is in the closed postion there is a gap of less than 1/16" where it isn't sealed off. Assume this is normal.
Anybody been here before?