SmokeSilver

Has anyone had this problem: I have a 97 E420 with 96K on it. When sitting in drive, say at a light, with rpms around 400-475, the engine will "stumble" rpms drop down a bit then back to over 500 then back to 400. It has never completely cut out, but close. At idle, then rpsm are around 600-650..is that normal? Seems like 750 would be normal.

Could this be caused by a bad/wornout refenence sensor (CPS)? If so, that would be an easy fix.

Thanks

mercedeslover

I have had the same problem and taken it in to the shop several times. They have changed different components but the problem still persists. Where is the sensor you mentioned and how do you change it?

I hope someone on this forum can help us with this annoying problem.

SmokeSilver

He advised me that we could spend a lot of time and $$$ trying to figure out which electrical component is causing it. He also drives a 97 E420 and has noticed the same thing. With the age and mileage on the car, he said components get old, etc. and as long as it is nothing more than a nuisance, don't worry about or spend big $$$ trying to track it down.

The Reference sensor is on the fire wall drivers side of the 420 just behind the valve cover with lile for colored electrical cords coming out of one end and a cover hosed looking thing coming out of the other...that hose one mine is royal blue color...

The sensor is on about $44.00 and you should be able to replace it yourself...I think.

Anyone else had this problem and had it fixed???

jrmd01

SmokeSilver

You need a another mechanic...Mercedes has this very famous problem and most official MB mechanic know how to approach this problem systematically to avoid throwing random parts on the car.

I've fixed numerous things on my 1986 300E to fix the idling problems. Every year since 2001 I've fixed it, only to have another component fail producing another idling problem the following year:

2001
Rotors
Cap
Spark Plugs
Wires

2002
OVP

2003
alternator
Found a loose vacum hose

2004
Nothing

2005
fuel pump (was making noise anyway...sign of impending failure)
fuel filter (first change since 1986)
temperature sensor (better, but not fixed)
injectors cleaned
spark plugs
ignition coil (fixed idling problem)
...
ANOTHER new idle problem started last month.
Next couple of things I'll try later this week
1. MAS potentiometer
2. O2 sensor
3. Fuel pressure regulator
4. CPS

Your mechanic is right on one thing...the older the car gets, engine components begin to degrade and "break down". But if he's competent enough, he should be able to fix your problem without randomly throwing parts at it.

If you're a decent "DIY" start with the simple stuff. Do a simple tune up...new plugs, new rotor, new distributor cap, higher octane gas, techron treatment, new filters, clean out the ICV, etc. If that doesn't work, then try replacing the more common components that fail or should be replaced as a preventative measure. ie. MAS, OVP, ignition coil, all sensors, relays, fuel pump, etc.

You can save a lot of money working on your own car. BEWARE...changing the above items may/may not fix your problems (so it can also cost you a lot of money too, so you'll have to "pick your poison"). Personally, I don't mind changing most of these things because they are things that are recommended to be changed on the MB maintenance records anyway.

If none of the above work, then you have a serious problem. Get an official MB mechanic to properly diagnose the car. At least you know you won't be charged $100 labor to change 6 spark plugs ($5 each) that you could have bought online for approximately $2 each new.

Good luck.

edit...
BTW: Just from your description of your idling problems, I highly doubt it's the "reference sensor" also called the crankshaft position sensor. Failure of that component usually presents as stalling at idle w/hard re-starting.

MBZ12

I posted this same problem a while back in this forum. https://mbworld.org/forums/e-class-w210/106912-car-started-sputtering.html The only difference is that my RPM's remained steady each time it stumbled while at a light. It went away and now only happens every once in a long while...knock on wood (tap, tap). The only thing I did was to change out the air filter....

RobertG

Smoke Silver;
check you gpm if it's degrading and your exhaust smells rich it sounds like your o2 sensors are getting tired.Cleaning the mas air flow sensor with electrical contact cleaner might help out too.

ruffrob

O2 sensors are EXACTLY the problem,I had mine replaced last Friday,and the 'stumbling' ceased. They can be obtained at www.thebenzbin.com for $177,and I got 2. The symptoms are just as you guys described. My mechanic explained that the air mixture was incorrect since they (the O2 sensors) were faulty. Good Luck...

SmokeSilver

Thanks! Did you replace them yourself or do the O2 sensors need to be done by a mechanic?

RobertG

If you can raise the car off the ground safely to get under it you can do it yourself.