Fuel System:
* Fuel Pump Relay: The relay might be failing when the engine compartment gets hot. This is a common issue in older Mercedes. The pump may be functioning fine when cold, but fail to deliver fuel adequately when hot.
* Fuel Pressure Regulator: This component regulates fuel pressure. If it's failing, it might not maintain the correct pressure when hot, leading to stalling. A leaking regulator can also cause a rich condition.
* Fuel Filter: A clogged fuel filter restricts fuel flow. While this can cause issues cold or hot, the heat can exacerbate the problem.
* Cracked or Permeable Fuel Lines: Heat can cause tiny cracks in fuel lines to open up, leading to fuel leaks and erratic fuel delivery.
* Intake Air Leaks: A vacuum leak can create a lean condition, making the engine harder to start hot. Heat may affect the size of the leak.
Ignition System:
* Crankshaft Position Sensor (CKP): This sensor tells the ECU the engine's rotational position. If it's failing due to heat, the ignition timing will be off, causing starting and idling problems.
* Ignition Coil: Similar to the CKP sensor, the coil can weaken with heat, resulting in a weak spark.
* Distributor Cap and Rotor (if applicable): High temperatures can cause carbon tracking in these components leading to poor spark distribution.
Cooling System (Indirectly):
* Overheating: While not directly causing the stalling, an overheating engine can lead to a variety of issues that *could* manifest as stalling or hard starting, such as fuel vapor lock. Make sure your cooling system is functioning correctly.
Other Potential Causes:
* Air Mass Meter (AFM) or Air Flow Sensor (AFS): A malfunctioning sensor, especially if heat-damaged, can send incorrect air/fuel ratio information to the ECU.
* Throttle Position Sensor (TPS): Similar to the AFM/AFS, a faulty TPS provides inaccurate information about the throttle position.
* Engine Control Module (ECU): Although less common, a failing ECU, especially one susceptible to overheating, could cause intermittent issues.
* Vacuum Leaks: Heat can worsen existing vacuum leaks, causing erratic engine behavior.
Troubleshooting Steps:
1. Check for error codes: If your 190E has a diagnostic port, try using an OBD1 scanner (or consult a mechanic with the proper tools) to retrieve any stored trouble codes.
2. Inspect the obvious: Look for visible signs of fuel leaks, loose wires, or damaged components in the engine bay.
3. Check the cooling system: Make sure the coolant level is correct and the car isn't overheating.
4. Test the fuel pressure: A fuel pressure gauge can determine if the fuel pump is providing sufficient pressure.
5. Check the ignition system: Inspect the ignition coil, distributor cap (if applicable), rotor, and spark plugs.
6. Test the sensors: Using a multimeter, test the sensors mentioned above (CKP, AFM/AFS, TPS) for proper operation.
Important Note: Diagnosing these issues requires some mechanical aptitude and the right tools. If you're not comfortable working on your car yourself, it's best to take it to a qualified Mercedes-Benz mechanic. They have the specialized knowledge and tools to properly diagnose and repair the problem. Mention the symptoms (stalling at idle and hard starting when hot) specifically.
