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Hi all, this is my first post on the forum. I've been reading and searching and there's a lot of great info here, so i decided to join.
I've been enjoying my 2002 E320 as it is a nice solid-feeling vehicle that has a comfortable ride. The car has about 170,000 miles.

Unfortunately recently it has started idling very rough when i come to a stop. It has even stalled. Sometimes I can restart it immediately and the problem will be gone and the car will drive fine. When the car is acting up it has a rough exhaust note like a pulse every other second (not running on all cylinders).

I pulled the codes with a generic reader and got codes P0300, P0302, P0303, P0305, P0306.

So, cylinders 1 and 4 are not throwing a code. Does/could it mean anything since these 2 are on the front end of the engine?

I cleaned the MAF but it made no difference.

I read that the these codes could indicate a bad cat. Is there an easy test for this?

Sorry for all the questions, and thanks in advance!
 

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Hello and welcome:)

Since you have misfires on both banks of the engine, I do not think it is the cats (typically one cat on one side fails, not both at the same time).

It seems to be a fuel / air mixture issue, rather than an ignition issue (because the misfires affect 4 cylinders at the same time. I am sure there are misfires at cylinders 1 and 4 but they have not reached the thresholds yet).

You say you cleaned the MAF, which part of MAF have you cleaned and with what ?

Have you had any maintenance and/or repair work prior to these misfires?

Have you tried removing the MAF connector with engine off, and starting the engine and see how it runs ?

After the test you should clean the connectors with MAF cleaner and let it dry prior to installing properly.

Also make sure that when you installed the MAF you had no air leaks at the intake manifold end (where the MAF unit is connected to the intake pipe with the steel clamp.

Make sure your air filter is clean, and the airbox clamps are installed properly.

Does your scanner provide fuel trims ? MAF airflow readings, engine coolant temperature ?
 

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Hi mrboca, thanks for the welcome and the helpful reply.

I had all spark plugs replaced and 2 of the coils, and 4 of the wires but still have the problem.

I recently replaced the alternator because when the idle problem occurs, the dash lights flicker and the voltage was reading a bit low. It didn't really improve things.

I removed the MAF and sprayed nearly an entire can of CRC MAF cleaner on both sides of the MAF. Didn't seem to help.

I also replaced the air filter at the same time.

I will go back over it and see if there are any vacuum leaks. I'll also try to run the car with the MAF disconnected.

The scanner I used was very basic and provides codes only--no details. I think I might try to buy a better one.
 

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Hi mrboca, thanks for the welcome and the helpful reply.

I had all spark plugs replaced and 2 of the coils, and 4 of the wires but still have the problem.

I recently replaced the alternator because when the idle problem occurs, the dash lights flicker and the voltage was reading a bit low. It didn't really improve things.

I removed the MAF and sprayed nearly an entire can of CRC MAF cleaner on both sides of the MAF. Didn't seem to help.

I also replaced the air filter at the same time.

I will go back over it and see if there are any vacuum leaks. I'll also try to run the car with the MAF disconnected.

The scanner I used was very basic and provides codes only--no details. I think I might try to buy a better one.
So starting from "no problems" with your car, what made you change the 2 coils and 4 wires ? Did you have problem only in two cylinders initially?

The dash lights flicker when the car is almost stalling due to misfire and recover. Probably nothing to do with the alternator. Make sure you read 13.5 to 14.5 Volts at the charging posts under the hood when the car is running.


When you say you cleaned the MAF, have you followed the sticky at the top of the forum page on how to clean it ? Sometimes people clean the wrong areas of the MAF and this does not help. You need to clean the the flat part INSIDE the cavity at the tip of the MAF insert, as well as the IAT sensor (outside diode looking thermistor device). Sometimes MAF cleaning will not help and needs to be replaced. That is why I asked MAF airflow readings from an inexpensive scanner.

Is the CEL on the display steady or flashing ?

You also may have a problem with the fuel pump and / or fuel filter (with built in regulator). You can get it tested with a fuel pressure gauge in 5 minutes connecting to a valve.

I think you will benefit a lot from a simple Bluetooth or wi-fi scanner and an application like TorquePro (for android) or similar for an Iphone. You will be able to read many of the parameters that will help telescope into the problem (like fuel trims, MAF, IAT, coolant temperature, Manifold pressure, system readiness, EGR status, etc etc.).
 
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