air mass sensor

[japimport]

hi everyone ive being looking on ebay and googling all day looking for an air mass sensor for my c200 95 it doesnt have a maf as most of the mercs do, mine hasnt got one im thinking should i have one, and all i seem to find on the internet is the mafs the reason why im changing it is when the car is at idle i can feel tremblings throughout the car only when idle ive already changed the engine mounts still no change ive checked my spark plugs to see if i can see anything unusual and they look fine i tried moving wires in engine bay to see if the engine reacts but no change anyone any ideas

 

[merc man]

could be a misfire, check the leads, failing that go to a parts dep in mercs and ask them if your car has a MAF, they will be able to tell you on the spot.

 

[grober]

Some of the early C200's had a different means to monitor the engine air requirement and don't have a Maff as such. The System is known as PMS manufactured by Bosch/Siemens. It monitors inlet manifold pressure rather than mass flow to judge how much fuel to supply to the engine. This gives the only decent explanation I have ever seen of the system in MERCEDES. http://www.hamsk.ru/murzik/WIS%20do...9%F1%F2%E2%EE%20PMS%20%F7%E0%F1%F2%FC%201.pdf
One possibility is that the following has happened :-

Function/faults Of PMS unit
4 piezo resistors, which are interlinked by means
of a bridge circuit, are located on an IC sensor
chip, which is designed as a diaphragm.
If the shape of the diaphragm is altered as a result
of the intake manifold vacuum, the piezo resistors
change their resistance. The change in the voltage
level which occurs as a result is used by the PMS
control unit as an operand for engine load.
Emergency running properties
In the event that the intake manifold pressure
sensor for detecting engine load in the PMS
control unit should fail, the injection time is
calculated as a subsitute from a map using the
throttle valve angle and engine speed. The throttle
valve angle is detected in this case by the throttle
valve actual value potentiometer (M16/6r1) in the
LLR actuator (M16/6) and passed to the PMS
control unit.

The PMS units are reckoned to be pretty reliable compared to MAF's but the at the age the car is???

The other possibility is if you have an ignition problem. The ECU or the 2 ignition coils can fail on these engines. The ECU driver transistors to the coils are glued to their heat sinks and when this goes they overheat and finally fail. Several firms offer a rebuild/exchange facility for these.

You need to get someone familiar with these engines to have a look at it and possibly read any fault codes to narrow down where exactly your problem is occurring Here is a PDF detailing the fault codes. http://www.hamsk.ru/murzik/Diagnostic PMS.pdf