I have the identical car with almost 60,000 original miles on it. In order to diagnose the problem you will need a little basic knowledge of Bosch K-Jetronic fuel injection, and the 2.3's ignition system. Modern autos have a single "Engine Computer" that handles both the spark and fuel requirements of the engine. This is not the case with an 1987 190e 2.3. The fuel system has its own ECU that is located behind the battery in the engine compartment, and spark is controlled by a electronic ignition module mounted in the engine compartment on a fender. The spark plug wires will be going into it. There are 2 types of ignition modules sold that year. One is very simple an can be bought on Ebay for about $72 new. The other is more sophisticated, and much more exprensive. I don't know the list price but I'm sure it is obscene. You will probably have to by it used unless you have very deep pockets.

If you wan't to check for spark, Sears sells an inductive spark tester, I believe made by a company called Liddle (can't exactly remember correct spelling) for around $10. You place it next to any spark plug wire and if voltage is passing through it the tester will flash each time the distributor passes spark to that wire. Check each wire individually while someone is cranking the car, or better, if the engine is running. It will isolate the miss. Be aware there might be more the one cylinder not firing correctly, so you may find more than one cylinder missing.

If it is only a single cylinder, you should still change all the spark plugs, wires, cap, and rotor. It doesn't pay to do only 1 cylinder.

If there is no spark going to any of the wires, it is likely the ignition module.

Next, if the problem is fuel related and your not knowledgeable as to the functioning of the K- Jetronic fuel distributor, have a professional mechanic remove the fuel line into the distributor and check that gas is reaching it. If not check the fuel pump.

You will also need to check the condition of the sensor plate. It is located under the air filter cannister. This car doesn't use a normal PCV valve, but a load of other sh_t. The sensor plate alway becomes gummy and full of oil, hampering its correct movement.

If gas is reaching the fuel distributor, than the fuel distributor could be bad and need rebuilding. It has to be done by a pro rebuilder, and they will ask for the old fuel distributor (core) as part of the deal. I have seen rebuilt ones selling in the $400 to $500 range, but don't run out to by a fuel distributor first. The injectors for the engine are very inexpensive and you can purchase a complete set for under $100 including delivery. I suggest you do the injectors before the fuel distributor. The injectors will require new rubber seals that are a few dollars each. Order them with the injectors. The injectors don't bolt in to the head. They are held in place by a retaining plate that can be re-used. Each injector has its own fuel line and it can be a pain the #@$ to seperate the fuel line from the injector. It is much easier to remove the other end of ther line going in to the fuel distributor. Note which fuel lines go where, because they're like a rubics cube if you try to re-install them without knowing the injector and fuel distributor port they were removed from.