1986 300E Stalling Problem Please Read
 

I took this car to a local imports garage. They have gave this car a complete tune up and checked everything and it still stalls. They tried the fuel distributor, fuel filter, OVP, fuel pressure regulator, distributor cap and rotor, plugs and wires, vacuum system. The only thing left is the computer. What could be the problem on this car??? Runs fine except for when you are at a stop the rpms surge and the car stalls. I am getting very frusturated. Thanks guys.

The OVP can be very hard to 'check'. It may appear to be fine functionally, and being a simple device - basically a relay - it would be easy to give it a clean bill of health and move on to the next suspect.

Problem is, this device tends to develop poor connections, either at solder posts on its circuit board, or at the relay contacts themselves. When that happens, voltage at its output fluctuates to the ECU, ABS, and elsewhere, causing erratic opertion of those modules. I had this happen even with a brand-new one I installed. Keep your suspicions about this device. Might be worth replacing as a matter of course if nothing else surfaces.

Steve

There's lots of stuff besides the computer.

In addition to a flakely OVP relay, you could have a bad idle air valve, or air leaks in the plumbing.

There are also a variety of sensors that provide information to the computer, which the computer uses to determine how much air the idle air valve should supply. If these are not functioning correctly, the computer will think that it should cut the power to the idle air valve. If this occurs at idle (instead of deceleration), the engine will stall.

There is a very large number of posts on this topic.

Sounds like your mechanic checked the basics. The next step is to drill down on the sensors. If it will actually die every time at idle, it should be fairly simple to find the problem.

I am with ctaylor, I would go for a very thorough cleaning of the idle control valve (ICV). And checking of the hoses attached to it. I had the same problem (with hunting idle) and the cleaning of the ICV fixed it. Remove it and use carburator cleaner.

Thanks for all the help. I'm going to mention the above to the mechanic to make sure he doesn't overlook anything.

Thanks again

You really need to find a tech who has worked with older high-mileage 300E's and 190E's because this seems to be a fairly common problem with them.

Your guy may be a good tech, but if he hasn't chased this problem before, you can waste a lot of time and money.

Another Possibility
 

Another common problem on higher mileage M103 engines is the airflow sensor pot gets worn out and will cause stalling, especially at idle. Do a search on "airflow sensor pot" for more information.