W 201 rough idle 1989 2 ltr 4 cyl fuel inj. Also hesitant acceleration.

Check for vacuum leaks. Check compression. Check condition of the plugs.

That would be a good place to start looking. Also check the O2 sensor.
SYSTEM/COMPONENT TESTS -1989 Mercedes-Benz 190E
Page 1 of 1
COLD START VALVE (190E 2.6L & 300 SERIES) TEST

1.
Disconnect cold start injector. Connect voltmeter to cold start injector connector. Remove crankshaft position indicator plug from ignition switching unit (Green cable located on firewall)
or install Protective Plug (102 589 02 21 00) on diagnostic socket.
Check voltage while cranking starter motor. Reading should be at least 10 volts. Disconnect fuel line on cold start injector. Remove injector and reconnect fuel line. Hold cold start valve into
container.
Disconnect electrical plug at thermo time switch. Connect terminal "W" on plug to ground with jumper wire. Below 41°F (5°C), it is not necessary to ground thermo time switch connector. Start
engine. Fuel spray from cold start injector should be cone-shaped. Disconnect ground test lead if used.
Dry any gasoline from nozzle of cold start valve. No droplets should form. Remove jumper wire. Install injector with new gasket. Reconnect wiring. Install relay and reconnect fuel line.
2.
3.
4.
NOTE:
During warm-up and at operating temperature, current to differential
pressure regulator is determined by coolant temperature sensor, O2 sensor and ECU.

2/4/2012

SYSTEM/COMPONENT TESTS -1989 Mercedes-Benz 190E
Page 1 of 1
OXYGEN (O2) SENSOR TEST

1.
Disconnect oxygen sensor plug and connect male terminal to ground. Start engine. Test sensor voltage between female terminal and ground. Sensor voltage should be near 450 mV. If not about
450 mV, replace oxygen sensor. If okay, go to next step.
2. Stop engine. Check wire from oxygen sensor plug to CIS-E control unit (terminal No. 8) for continuity. Resistance should be about zero ohms. If resistance is not about zero ohms, repair
circuit. If okay, test is complete.

2/4/2012