Everything you ever wanted to know about D-Jet:
http://members.rennlist.com/pbanders/djetparts.htmEverything you ever wanted to know about the operation of the different ECU's for our cars:http://members.rennlist.com/pbanders/ecu.htm
And a more specific answer to your question:Q: How can I change my mixture only at idle?A: Idle mixture can be adjusted by using the idle mixture adjustment knob on the ECU. Note that some early 1.7L ECU's did not have an adjustment knob. Clockwise clicks richen the mixture, counter-clockwise clicks lean the mixture. The factory made a mark on the plastic surround of the knob to indicate the "factory" setting, the correct mixture for proper operation is usually within +/- 3 clicks of this position. I suggest that you use an air/fuel meter to adjust the idle mixture to the factory setting of CO. If the proper setting of CO cannot be achieved within the range of the idle mixture adjustment knob, then it is likely that there is a problem with the FI system - mismatched FI components (see my D-Jetronics Parts Document for assistance), failed FI components, or a maladjusted engine (valve clearance and/or ignition timing and dwell, other ignition faults, vacuum leaks, etc.). While I have taken readings on my car at idle, they don't apply to stock motors because I have an aftermarket cam (apparently), and my mixture is richer due to the low idle manifold vacuum due to this cam. From in-car road measurements (using a Heathkit Air/Fuel meter) on my 2.0L with 1974 FI components, my idle mixture is about 13.3:1 (lambda of 0.90). I have not measured the full-load mixture on other stock 2.0 or 1.7L cars in good tune.
Q: Does the idle mixture adjustment knob on the ECU only affect the idle mixture?A: Yes, with one exception. It has no effect unless the throttle is closed and the idle switch in the TPS is on, indicating the idle condition. For ECU's with the OS circuit (e.g. the 0 280 000 052 or 0 280 000 015), note that when the engine speed drops below the threshold level of the OS operation, the over-run mixture is partially controlled by the idle mixture knob position. If you have an ECU with or without the OS circuit, and you have light backfiring during over-run, adjusting the idle mixture knob to a slightly richer mixture (1 or 2 clicks clockwise) may help.