STILL having problem with high idle, then turning off
1987 420SEL, approximately 150,000 miles
Symptoms - starts up fine. In fact, after sitting almost a week, I bet the engine didn;t turn 3 revs by the starter motor and she was running smooth.
Temperature rises, engine running smooth. Today, at first around 1100 rpm, but then drops to the 800-900 range. In the past, it has started at less and dropped to 600 or so, but today it started at about 1100.
When the needle hits about 50c, the idle sort jumps up and down for a while, and then as the engine gets a little warmer, the engine speed goes up to 1500 and increases all the way to about 2200, and then finally cuts off and shuts down.
If immediately restarted, idle is immediately high and shuts off.
If allowed to cool down, will start right up, idle around 750 or so, then jumps up and dies.
1) Tried different known good OVP. But I would think if the OVP was bad, it would go to high idle right away. If either the original or the other is disconnected when in low idle, the idle jumps. When running at 2200 rpm, and the OVP is unplugged, no idle speed change.
2) Tried a different Fuel Pump Relay. Opened them both up. Wiggled things around. No change. When the idle does get to 2200 and runs there, I can see the fuel pump relay points separate and stop fuel flow, so the engine ndies. IF I spray stater fluid into the air horn, the engine will run on ether, so it still has ignition.
3) Tried a different CIS computer - same problem
4) Took the Idle Control Valve off and cleaned the heck out of it. Prior to doing this, the idle was always about 1500 or so. After doing the cleaning, the idle would start cold below 750. If the unit is unplugged while in low idle, the idle immediately jumps up. If replugged back in, it drops. When in high idle, and unplugged, no change.
5) Tried a different ICV - same everything.
6) Tried a different Idle Speed Control black box. Actually tried two different ones because one was from a 560 engine and had a different part number. Unplugging any of them at low idle causes the idle to jump way up. Plugging either back in, and the idle drops. When in high idle, unplugging any of them causes no change.
7) I've tested the B11/2 switch and it seems the resistance values follow the prescribed temperature/resistance levels. Tried a different B11/2 switch. Same symptoms.
8) If one of the wires is disconnected from the B11/2 switch, the idle changes and the engine runs differently (I am guessing this to be the wire to the EZL) at low idle. I did not try at high idle. The other wire, when disconnected seems to make no change.
I've searched every forum and found a lot of info but I am at a loss. I need to buy a duty-cycle meter to test some components out.
In looking and reading, I see that there is an input telling the computer what gear the selector is in. There is something called the altitude correction unit.
Some have suggested vacuum leaks. The idle does not jump up until the coolant temperature gets above about 50c. I have sparayed with ether or carb cleaner all over the place when in low idle with no rpm change. Done so in high idle as well with no change. Because of this, I have ruled out vacuum leaks.
Once it gets into the high idle mode, around 2200 rpm, it will run there for a while, then die. Something is "telling" the fuel pump relay to disengage as described above. What would cause that to happen? There is a fault somewhere and the computer is interpreting it the failure is fatal and knocking out the fuel.
I read somewhere that the fuel pump will be turned off if the car thinks it has been in accident.
From what I've read, the EZL should not be causing these symptoms.
The engine does not seem to be running too rich or too lean.
I also found this procedure - what/where is this differential pressure regulator mentioned below:
Coolant Temperature Sensor
1. Disconnect plug from coolant temperature sensor. Using ohmmeter, check resistance between sensor terminal and ground. Measure resistance at 2 different temperatures. If readings are not correct, replace coolant temperature sensor. If coolant temperature sensor is good, go to next step.
2. Connect meter adapter cable between differential pressure regulator and multimeter. Set meter to mA scale. Disconnect wire to O2 sensor. Turn ignition on and check current reading. At operating temperature, reading should be 7-9 mA.
3. At coolant temperature of 60°F (20°C), reading should be 9-14 mA. If wiring to temperature sensor is disconnected, reading should be 114-132 mA. If readings are correct, unit is okay and test is completed. If readings are not correct, go to next step.
4. Disconnect plug to differential pressure regulator. Resistance reading of regulator should be 18-21 ohms. If reading is not in range, replace differential pressure regulator. If reading is good, go to next step.
5. Check voltage at plug connector for coolant temperature sensor. Voltage should be 5 volts. If there is no voltage, repair wiring. If voltage is correct, go to next step.
6. Check wiring between ECU and differential pressure regulator for continuity. If continuity tests good, replace ECU. If no continuity, repair short in wiring.
1. Disconnect airflow sensor potentiometer (position indicator). Make sure fuel pump is NOT running. Connect ohmmeter between terminals No. 14 and 18 of potentiometer. Reading should be 3200-4800 ohms with sensor plate in rest position.
2. Connect ohmmeter between terminals No. 14 and 17. Resistance should be 550-1050 ohms with sensor plate in rest position. With sensor plate at fully open position, resistance should be 3760-5640 ohms. If readings are not correct, adjust or replace potentiometer. If readings are correct, go to next step.
3. Connect meter adapter cable to differential pressure regulator. Set multimeter to mA scale. Connect 2500-ohm resistor wire between coolant sensor wire and ground to simulate coolant temperature of 60°F (20°C). Disconnect microswitch and turn ignition on. Current reading should be 9-14 mA. Deflect sensor plate to full open position and check that current reading increases. If readings are incorrect, go to step 5). If readings are correct, go to next step.
4. Disconnect differential pressure regulator. Measure resistance of regulator. If resistance is in range of 18-21 ohms, regulator is good and test is complete. If reading is out of specified range, replace differential pressure regulator.
5. Measure acceleration enrichment voltage between terminal No. 18 of sensor plate potentiometer and ground. Voltage reading should be 7.4-8.6 volts. If not, repair wiring circuit. If reading is correct, go to next step.
6. Measure voltage between terminals No. 18 and 14 of connector to airflow sensor potentiometer. Reading should be 8 volts. Also measure between terminals No. 17 and 14 of connector, which should give reading of 7.5 volts. If readings are not correct, repair wiring circuit. If readings are correct, go to next step.
7. Check wiring between ECU connector and differential pressure regulator connector. See MERCEDES-BENZ 190E CIS-E WIRING DIAGRAM for wiring color and terminal numbers. If resistance reading is zero ohms, circuit is good and ECU should be replaced. If reading indicates open circuit (infinity), repair wiring.
1. Connect meter adapter cable to differential pressure regulator. Set multimeter to mA scale. Unplug O2 sensor under right front floor mat. Current reading at operating temperature should be 7-9 mA. If reading is not correct, test coolant temperature sensor as previously described. If reading is correct, go to next step.
2. Disconnect Green wire of ignition switching unit or install Protective Plug ( 102 589 02 21 00 ) into diagnostic socket. Simulate coolant temperature of 60°F (20°C) by connecting 2500-ohm resistor wire between coolant temperature sensor lead and ground. Crank engine for about 3 seconds and let key return to "ON" position. DO NOT turn ignition off.
3. After 4 seconds (including 3 seconds of cranking), current reading should increase to 24 mA. After 20 seconds, current reading should drop to 9-14 mA, which is basic warm-up current value. If readings are correct, test is complete. If readings are not correct, go to next step.
4. Connect voltmeter between ECU connector terminal No. 24 and ground. Crank starter motor. Cranking voltage signal (terminal No. 50 voltage) should be 10 volts. If not, check and repair wiring. If voltage is correct, go to next step.
5. Check wiring between ECU connector and differential pressure regulator connector. See MERCEDES-BENZ 190E CIS-E WIRING DIAGRAM for wiring color and terminal numbers. If resistance reading is zero ohms, circuit is good and ECU should be replaced. If reading indicates open circuit (infinity), repair wiring.
Is there anything else I can check, and how do I check it?
This is my son's car and I won't be back until Saturday.
Any help would be appreciated.
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Last edited by waybomb; 02-16-2010 at 03:43 PM.