Mercedes Benz repair: 190E 1988 Starting system, neutral safety switch, auto repair shop


Question
I own a Merc 190E 1988 2 litres petrol.
About 1 year ago the car used to go off while driving. Once stopped I had to wait 3 to 5 minutes before starting it again.
Nobody was able to find the problem, Then I thought It may be the allarm System. Eventually I took it off and the car started again without stopping any more like it used to.
I now have been driving it for 2- 3 weeks, I recently also changed the exaust, the battery, sparking plugs and the distributor rotor.
Nowdays I have been having a different problem. In fact the car sometime starts and sometime it doesn't. It may start 5 times in a day and not at all the day after.
I thought it may also been a timing problem.
I have noticed that every time I attempt to start the car, just after turning the key half way, and there is a whizz noise coming maybe from the engine it starts succesfully.
Help would be much appreciated.

Answer
Four possible issues:
#1. The neutral safe start switch (on the transmission) may be bad.
Broken Neutral Safety Switch and replacing shifter bushings
http://www.mercedesshop.com/shopforum/showthread.php?p=646647#post646647

#2. The ground cable from car body to transmission may be loose/broken.
Add a new ground cable from battery negative directly to the engine.

#3. The starter may be bad.
Any good auto repair shop can test this.

#4. Ignition switch unit may be damaged.
How not to remove the ignition lock! Butchery at its finest.
http://www.mercedesshop.com/shopforum/showthread.php?t=148451

Fixed my lock cylinder on driver's side
http://www.mercedesshop.com/shopforum/showthread.php?p=1056089&posted=1#post1056...

Ignition Cylinder Tumbler replacement; mixed diesel/gas
http://www.mercedesshop.com/shopforum/showthread.php?p=1065596#post1065596

Ignition Cylinder, Switch, or Housing?
http://www.mercedesshop.com/shopforum/showthread.php?t=145832