Hello everyone, although this is my first post I've often used searched this forum with great results.

I drive a 99' Ml320 with over 150k. The car began stalling intermittely this fall, usually after red lights. Because I don't do much driving I continued to drive the car very lightly and carefully. Immediatley after the first couple stalls it began losing power and eventually die while stopped. However I would be able to restart the car and crawl home. The follwing days after, the car would start rough, idle rough for maybe 2 minutes, the die. I've noticed if I pressed the accelerator the rpms would drop, and as I let go the rpms would jump. The harder I pressed, the harder they fell. If I very slowly pressed the gas the rpms would follow accordingly. I read the codes at the time and it came back with random misfires (I think it was cylinders 2,3,6), all four O2 sensors, and fuel trim. I accidentally cleared those that is why I am not exact.
At any rate I've replaced...the CPS this past summer, the brakelight switch in September, as well as all new spark plugs (Bosch Platinum+4), all new wires (karlyn), new MAF, and air filter. I've also removed and cleaned the EGR valve. After all of this the car is still behaving the same. I have rescanned the codes and this is what comes up....

P0300 Random Misfire
P0303 Cylinder 3 Misfire
P0302 Cylinder 2 Misfire
P0301 Cylinder 1 Misfire
P0110 Intake air Temp Sensor 1 circuit
P0130 O2 Circuit

I find it a little odd that before the repairs the misfires were truly random, after the spark plug change the misfires are all on the same side. Any help is really appreciated. Sorry about the length but I figured the more detailed the easier it would be to diagnose.

You've done most of what I would suggest and from my experience causes similar symptoms. Other possibilities are bad plug wires, a loose plug wire or a bad ignition module. Possibly a bad cam PS but that usually throws a code.

Dying while pressing the accelerator is in my experience a symptom of poor ignition (which floods the engine) or too rich a mix (which floods the engine ). But right now there isn't any way that I can tell which is causing the problem. You may even have more than one problem causing this.

Since there can be so many causes to this I would take the vehicle to a shop with a good engine monitoring system that will record multiple sensor readings and try and duplicate the problem with them monitoring it. Be prepared to pay a couple of hours labor for this.

The codes suggest that the passenger side of the engine is shutting down.
That suggests to me that you "might" have excessive exhaust backpressure.
I would have the exhaust backpressure tested on that side.

Has your ML had the catalytic converter recall??


Using Bosch +4 plugs isn't a good idea. They are "cheap" aftermarket JUNK!

If they were any good at all MB would use them from the factory!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
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Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I have no idea if the car has had the cat converter recall....How would I know?

What are the original plugs? Is it necessary to re-change the +4's back to the factory plugs?

Call a dealer & see if the truck has any open campaigns.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I just found out the cats were changed about 3 yrs ago.

Would faulty O2 sensors cause these same symptoms? I've been getting O2 codes off and on for a while now. Would that be a good place to start?

Why don't you post the codes, many times O2 codes mean other parts are to blame & NO they won't cause that type of problem.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

The last time I ran the codes the only O2 related code was P0130.
I recall in the past I had all four O2 codes thrown at me.

On another forum someone mentioned it may be fuel related i.e. fuel pump or fuel filter. What are the chances that may be the culprit?

Ethanol related.....