R107 Stalls When Warm or at Idle

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An R107 that starts and runs but stalls at idle, or dies when it gets warm, is frustrating. The good news is that the causes are well known. On K and KE-Jetronic cars, the usual suspects are vacuum leaks, the idle control system, fuel pressure and ignition.

Warm stall causes

• Vacuum leaks that get worse as rubber warms and expands.
• Fuel pressure problems, including a failing fuel accumulator that lets pressure drop when hot. See fuel pressure test.
• Warm-up regulator or control pressure problems on K-Jetronic cars, making the mixture wrong when warm.
• Coolant temperature sensor faults on KE-Jetronic cars, giving the wrong signal to the control unit.
• Ignition faults that appear when hot, such as a failing coil or ignition module. See ignition coil.

Idle stall causes

• Idle control valve sticking or not getting the right signal. See idle control valve.
• Throttle linkage binding or misadjusted.
• Vacuum leaks at the intake boots, hoses or injector seals.
• Base idle set too low.

Fuel accumulator

The fuel accumulator holds pressure in the system after shutdown so the car restarts easily when hot. A failed accumulator causes hard hot starts and can contribute to stalling after restart. Test by checking residual pressure after shutdown with a gauge.

Vacuum leaks

Listen for hissing with the engine idling. Check the intake air boot between the airflow meter and the throttle body, the injector seals, the vacuum hoses to the brake booster and the climate system. See vacuum leak symptoms.

Step-by-step check

1. Check for stored problems on KE cars, if your car supports blink-code or duty-cycle checks; see lambda duty cycle.
2. Check for vacuum leaks.
3. Check the idle control valve operation.
4. Check fuel pressures, including residual pressure.
5. Check ignition when hot.
6. Check the coolant temperature sensor.

Quick answers

• Why does it stall when I come to a stop? Often idle control or a vacuum leak.
• Why does it stall only when hot? Often fuel pressure, temperature sensors or ignition.
• Can a bad fuel pumphttps://www.amazon.com/s?k=Mercedes+fuel+pump+relay&tag=margomoments-20″ rel=”sponsored nofollow noopener” target=”_blank”>fuel pump relay cause stalling? Yes, an intermittent relay can cut fuel; see OVP relay.
• Is it the EHA? On KE cars, the EHA can cause mixture problems; see EHA valve.
• Can a weak fuel pump cause warm stalling? Yes; check delivery volume as well as pressure.
• Does the idle speed need adjustment? Only after fixing the cause; do not mask faults with a higher idle.