BMW Repair: Engine doesnt respond well, exhaust gas analyzer, fuel additives

Question
It is manual.  So the best thing is to take it to the mechanic to analyze,  I beleive.  Do you hav any suggestions what I can do before I take it to the mechanic? I am trying to fix It if there is more than the dirty carburators or spark plugs.  What do you call the "head"?  I would very much appreciate if you can clarify.  I took the plactic cover of the engine but I still couldn't find the spark plugs.  It could be a serious problem or a simple problem?  It's only stutering after start everytime I stop.  Thanks again.
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Followup To
Question -
Hello.  I have 1993 325i BMW, 70K miles.  Within the last few months, I had a several problems.  First, the car got overheated and water pump was replaced.  Then 2 months later, it broke down again completely and the fluel pump had to be replaced.  Now, everytime when I start driving, the car doens't respond as if there is not enough fuel or too much air.  Once it goes to a higher speed, it runs fine.  I tried to see the spark plugs are OK, but I couldn't find where they are.  I will put the gas treatment next time I pump the gas to see if it'll make it better.  Do you have any idea what causes this problem and where I can find the spark plugs?  Thank you very much for your help!
Answer -
auto or manual?
the problem most likely will not be fixed with fuel additives.  What you need is to have your car put on a ossciliscope or ignition scope with an exhaust gas analyzer.
Or you can have the codes pulled with a scanner (the computer should tell you what it's having problems with).
the plugs are screwed into the head.
-cheers

Answer
Your car doesn't have a carburator.  the head is on the top most portion of the engine. I believe the plugs are on the right side.  It could be a simple problem but impossible to diagnose without looking at it.
I can't think of anything you could do to prep the car for the mechanic, the codes need to be pulled.
-cheers