Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1990 Mercedes Benz 560SECFACTORY OEM SERVICE PROCEDURE
Idle & Full Load Contact Test
- Connect On-Off Ratio Tester (KDJE-P 600) to diagnostic socket and turn on ignition. On-off ratio should be about 70%. Move airflow sensor plate about .80" (20 mm). On-off ratio should be about 10%. Go to next step.
- If reading is 70%, throttle valve contact does not close or there is an interruption in wire to idle speed contact. Close airflow sensor plate. On-off ratio should be 40%. Go to next step.
- Open throttle valve fully. On-off ratio should be 20%. If ratio is not correct, replace full load contact. If okay, test is complete.
Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.