Mercedes-Benz Forum banner

middle vents

2K views 10 replies 5 participants last post by  Minnet 
#1 ·
hi i have a 1995 s 320 with 250thousand miles Two problem the car shakes after a little while, sometimes if i put on the ac or climate then i i restart the car it goes back to normal and power is resumed i lose acceleration power the car backfires and it hesitate these are the symtoms before i restart car ,, 2 the middle vents do not work!!! does someone have advise!!! thank you
 
#3 ·
Sounds like ignition problem, but could also be engine control, anyway something electrical (if it really runs normally after having been restarted).

The fact that the probem typically occurs when switching on a/c could indicate that the engine control cannot adapt the changing load condition and the fact that i resumes normal operation after restart could indicate that it then goes into "limp home mode".

Inspect the engine wiring harness to see if wires are cracked.

Otherwise I would suspect air mass sensor.

The middle vents are controlled through a vacuum circuit. I don't believe it has any connection to the engine problem.
 
#4 ·
the car is going into a "limp home mode" to protect the engine components, specially pistons, from impact damage due to the pinging caused by misfiring, thats why only 66% of the engine torque is allowed, 50% of the throttle pedal travel, and less than 10% of the driving pleasure!

chances are, most of your ignition components are fries, as well as your engine harness, and throuttle body. especially at such mileage.

check all of these components to find the problem.

the W140 IS IN FACT a reliable car, but its not beyond laws of physics, a W140 WILL run forever, but i needs to be serviced very well.

Bayhas M. Kana
W140 @ 272150 Miles



Minnet said:
Sounds like ignition problem, but could also be engine control, anyway something electrical (if it really runs normally after having been restarted).

The fact that the probem typically occurs when switching on a/c could indicate that the engine control cannot adapt the changing load condition and the fact that i resumes normal operation after restart could indicate that it then goes into "limp home mode".

Inspect the engine wiring harness to see if wires are cracked.

Otherwise I would suspect air mass sensor.

The middle vents are controlled through a vacuum circuit. I don't believe it has any connection to the engine problem.
 
#8 ·
roysofia said:
is this expensive
why did you buy a mercedes if you are going to ask such question?
 
#9 ·
roysofia said:
is this expensive
About 100 USD.

And yes, this could be the problem (among other things).

Still try to inspect the engine wiring harness as the first thing, because this does have at limited lifetime, because it is the first generation made of biodegradable insulation material, which starts cracking after some years. Leaking currents in it can cause all kinds of funny behaviour.

If it is OK, you can start looking other places. The problem can be in the ignition (fx. ignition coil as suggested) system or in the injection system (fx. the air mass sensor as also suggested). Any of the places could cause the computer to be confused and enter "limp home mode".
 
#11 ·
roysofia said:
:bowdown: thank for help,, i fixed the middle vents the vacuum was unplugged very simple i checked harness pretty good condition i cleaned airmmass system no change so next ignition coils does anyone have a diagram can i do this myself is it easy?????
Are you having one common ignition coil or does every spark plug have one each?
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top