1988 Mercedes 190E Hard Start When Warm
I know that cranking times of four seconds is normal for the CIS-E injection systems. Do not depress the accelerator pedal while cranking.
A few things to check are the Airflow Sensor Plate for binding or rest position is not correct.
One test you can perform is to check the mA at the electrohydraulic actuator while cranking the engine. If a negative current (approx -40 to 60 mA) is measured, the CIS-E control unit recognizes deceleration shutoiff. A remedy is to replace the ignition control unit.
Check to see if the correct cold start valve, spark plugs and fuel pump relay with cold start activation up to +60C is installed.
I see there is a problem with the intake valves pulling thru the seats, and jammed hydraulic compensation elements.
I assume your mechanic has tested the fuel injector valves, but make sure the fuel distributor is working normally.
There is a fuel pump check valve located external of the fuel pump that could be allowing fuel to empty and cause a long crank time.
Good luck
Suggested Repair
Do not press the accelerator while cranking. Check the airflow sensor plate for binding or an incorrect rest position, measure electrohydraulic actuator current while cranking (negative current can indicate deceleration shutoff and may require an ignition control unit), and verify the cold-start valve, spark plugs, and fuel-pump relay. Also inspect intake valves and hydraulic compensators, injector valves, the fuel distributor, and the external fuel-pump check valve for fuel drain-back.
Conversation Summary
A 1988 Mercedes-Benz 190E 2.3 cranks but needs several attempts to start every day, and it starts more easily in cold weather than when warm. A Mercedes specialist was unable to find the cause after an overhaul. The expert noted that several seconds of cranking can be normal on CIS-E and advised not pressing the accelerator while cranking. Suggested checks include the airflow sensor plate, electrohydraulic actuator current, cold-start valve, spark plugs, fuel-pump relay, intake valves and hydraulic compensators, injectors, fuel distributor, and the fuel-pump check valve.
