Sounds like the idle speed contacts on the throttle body are bad. If this switch is bad you will get a high idle and low Lambda at idle (this is not the microswitch that is on the linkage). There is a wire that runs from the throttle body to a connector with 3 terminals. Unplug it and check the resistance with an ohmmeter. There are actually two sets of contacts - one for idle and one for wide open throttle with a common return. The idle switch should read low resistance (0 to a few ohms max.) and go to infinity when the throttle is moved off of idle.