Souk, thanks so much for the re-assurance. I was at a local bookstore and couldn't find the Bentley manual, but I did buy "How to Tune and Modify Bosch Fuel Injection."

I think I am beginning to get an understanding of whats going on with the K-Jetronic with Lambda Sensor.

Let me summarize and tell if I am getting close

1. Throttle body opens decreasing air pressure between throttle body and air distributor.
2. Plate in air distributor raises due to pressure change
3. plate is attached to lever that raises plate in fuel distributor
4. rate of fuel dumped to injectors is increased.

If this is right, I still don't understand how the lambda sensor controls anything or how the idle microswitch on the throttle body forces the engine to stay at idle.

Thanks everyone, I actually feel a little smarter
Matt

The lambda circuit will richen or lean the mixture. It senses a change in the air fuel ratio with the O2 sensor. It is not as exact as it should be as the change from rich to lean happens fairly quickly as detected by the oxygen sensor. There was recent discussion on Rennlist about the O2 sensor, and from what I gather, the resolution of an O2 sensor/circuit between rich and lean is not very good. I think the mixture swings back and forth between rich and lean, and the lambda circuit eventually finds a nice median where it thinks is a good A/F ratio, based on the frequency of the swing. Basically, the lambda circuit adjust the mixture as the O2 sensor voltage fluctuates until the frequency eventually it settles out. As I have learned from PID loop tuning on the pipeline, digital tuning of such a system (or the system that Bosch was aiming for) is not easily done at low cost, the lamba circuit is fairly simple and it works OK but it's not the the best (by cost efffective for the purpose it was developed), but it is a good case/arguement that anolog or pneumatic systems work very well for what they cost.

Anyways, I don't have a motor w/ lambda circuitry so I'm have avoid having to learn the system. So take the above for what it's worth (my $0.02). Most folks just disable the circuit by unplugging the O2 sensor. I think that fools the lambda circuit into thinking it has a stable O2 reading so it stops trying to adjust (thus no more surgin idle on those cars). You then adjust the mixture, at the fuel distributor/air flow sensor arm, to a level you want.

Do out rule all other features of your fuel or ignition system. I find that troubleshooting complex systems works best if you work on one part of the system at a time and by process of elimination, you should find your faulty part.

Others will chime in, so keep asking questions. That book you picked up is good, but I was a bit disappointed with its depth. You'll learn as you go along, but be patient and don't ruch into anything you are not sure of.

Good luck.

Try these as well:

http://www.volvoclub.org.uk/k_jetronic.htm

http://www.users.bigpond.com/INTERJECT/KSITEPLN.HTM#K-JETRONIC%20schooling

Also, keep in mind that the 450sl Mercedes used this system as did Volvos, etc. Lots of information in theory out there, so check out the Merc list or otherwise if you want to become a guru.

John