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Car stalls and dies

I have a 1989 300E gasoline Mercedes with 205,000 miles. For the past 2 months is has stalled/died when I stop at a stop light or slow down for a turn or yield sign. This happens inconsistently and can go for days without stalling. The Mercedes repair service has replaced a filter (not fuel filter I don’t think) for a cost of around $900. It continued to stall so they replaced a fuse that was burned out that caused the engine to die because the fan did not cool it. It continued to stall. My battery was 8 years old and I was told I needed a new battery and had that replaced. The car ran well for about 3 weeks but stalled/died 4 times today when I stopped at a stop light or slowed at a yield. I am concerned about causing or being in an accident with my car stalling. What do you suggest? Help!!

I am going to take a shot and conclude your car uses CIS injection of some variant. Because of this I would be looking for vacuum leaks around the injectors or cracks in the rubber tubing of the intake system. Since there are many reasons for a car to stall my two suggestions are no where near a complete list but the are pretty easy to test for. You can check the intake tubing visualy (squeeze it and look for cracks) and the injector seals can be checked with carburetor spray. Spray around the injectors and if you get a rise in idle speed they are leaking.

If these quick checks do not reveal the problem use a stratagey (just dont throw parts at it) preferably from a troubleshooting chart. How are you set for a manual or are you just looking for suggestions for your mechanic (which I say is OK) but don’t tell the mechanic what part to replace just ask if they can assure you that the problem is not a vacuum leak somewhere and suggest the injector seals.

Does the engine usually idle smoothly? If yes, it may be the lockup torque converter isn’t unlocking when car speed drops below 30 mph, as it should. If you are slowing, and the engine starts to buck, put the gear shift into neutral. If the engine smooths, have the lockup torque converter circuit checked.

Could be faulty idle air control (IAC). Most engines have one.

Yes, the car uses the KE CIS injection system. Agree that both injectors and vacuum leaks are reasonable things to check for. Is check engine light or ABS light on? Has routine maintenance been kept up: plugs (non-resistor copper core only, like NGK BP5EFS), plug wires, distributor cap and rotor, air and fuel filters? Next, if your idle air control (IAC) valve, crank position sensor (CPS), fuel pressure regulator, ignition coil, fuel pump relay and overvoltage protection (OVP) relay are still original, those are candidates for diagnostic testing. (In fact, the OVP has been upgraded since 1989 and if you still have the OVP with a single fuse on top, it should be replaced with the newer 2-fuse relay no matter what else you do.) Then I’d look at the fuel pumps. Finally, the throttle valve switch and airflow sensor position indicator. Each of these has straight-forward diagnostic procedures in the factory service manual that you or your indy can readily perform to rule them in or out. If all of these test good, you could be faced with big $$ in the ignition control (EZL) module or the KE control unit.

I do not have a manual and am looking for suggestions for the mechanic. I will ask about the leaks. Thanks. Josie

The engine dies smoothly. It does not sputter and I don’t realize that it has died until I see the lights on the dash and the car stop. I will ask the mechanic about the lockup torque converter circuit. Thanks, Josie

I will ask the mechanic about this. Thanks, Josie

Wow! I will take this e-mail to the mechanic and talk with him about this. I have had regular service for the first 100,000 miles with the dealer and have had regular service since then with an authorized Mercedes repair place that I trust. Thanks, Josie

Yes…this system has all the systems mentioned. If the car is stalling as you come to a stop the “most likely” issue is a bad “Throttle position sensor” This is a small black switch that is screwed onto the throttle linkage under the Air cleaner. This is the switch that signals the computer to tells the idle solenoid to maintain the idle at stop. Easy to replace on your own. If I recall this has one electrical connector and two screws on top. Approximate part cost $25. If you have an meter, the connector can be removed and test the switch by moving the roller in and out. You should notice continuity between the contacts. Be careful as you remove the plastic tubes and connectors they are brittle and may snap off. If you do break them you can buy them separately from a dealer.