WORKED ON MY OWN E-320 SINCE THE WARRANTY RAN OUT/ BEAUTIFUL CAR! SOOO- OK, CAR STARTS IDELING A LITTLE ROUGHT PULL A 400 CODE. CAR HAS ORGINAL EGR VALVE- SO WHAT THE HECK I REPLACE IT WITH A NEW ONE, CLEAN TUBE ECT. RESET CEL. CAR RUNS FINE, DAY LATER CEL COMES ON AGAIN SAME CODE 400 PLUS PENDING PRECAT SENSORS. AGAIN WHAT THE HECK? I REALIZE SENSORS NEED TO BE REPLACED. I PURCHASE BOSCH AND CAREFULLY SPLICE AND SODER/4 WIRE INSERT ALL 4 DOWNSTREAM AND PRECAT.NOTICE OLD SENSORS DO HAVE CARBON BUILD UP. CAR RUNS FINE TO WORK. ON WAY HOME /WORK CEL COMES ON AGAIN. OBD READER COMES UP WITH OLD 400 CODE/EGR FLOW, AND AND---- 4 NEW O2 SENSORS WITH A HEATER MALFUNCTION!!! WOW I WAS BLOWN AWAY! ANY HELP WOULD BE APPRECIATED. OUR LOCAL DEALER IN NOT TO REAPTABLE AND WOULD ONLY USE THEM AS A LAST RESORT. I DO ALL BRAKE/OIL/FILTER MAINTAINANCE MYSELF AND NEVER RAN INTO A PROBLEM LIKE THIS BEFORE. CAR ACTUALLY RUNS FINE EXCEPT SOMETIMES WHEN COLD A HARDER START- thanks, jack

 

How long ago did you replace the fuel filter?

 

Thanks for your quick reply; 15,000 miles ago; I have a spare Mann filter/ n waiting n the closet; will put it on tommrrow after work, let u know what happens. If anyone elese has idea's please let me know. Thanks again, Jack

 

have u got a donour air mass sensor ,if so try that thats the remady..........let me no hw u get on NAZ

 

Do you know how to checkif the start-injector is leaking?
The reason I ask is sometimes the start injector will leak, and constantly pour fuel into the head making the entire engine run too rich. The extra soot then clogs the O2 sensor, fouling it out. The soot is the give-away; the sensor should bewhite or clean.

Also don't throw the old O2 sensor away; you might be able to clean it, and use it as a test unit for troubleshooting in the future.

I don't know why you had to soldier anything; there is a connector plug for the 02 sensor under the passenger seat. Of course some people do not like connector plugs because they are often the problem themselves.

Blue

 

Thanks Bluesilver for the information. I took the car for a long hard run today after replacing the gas filter last night also added some seafoam. To my amazement the EGR code 400 indicating a flow malfunction DID NOT come out on the codes when the CEL finally came on about 90 highway miles/ avg 80-95 mph. Yet, when I got off the turpike to grab a sandwhich, (stop-go) the CEL comes on and all 4 codes refering to each sensor a heater malfunction. I 'am home now and the car is to hot to work on. Would like to pull the front sensors to see if they are sooted up.
PLEASE inform me as to how to check to see if the start-injector is leaking. Sounds very plausable. The engine is running to rich.
I don't even know which injector is the one you are refering to. Thanks again, Jack-------- PS nice looking E car, will post a picture of mine when I straighten my problem out.

 

Thanks, MAS was replaced new 6 months ago. I clean this sensor every oil change with CRC cleaner product. Jack-

 

What year is the car? and what model?

Blue

 

1998 E-320 not a 4matic.
Pulled the bank 1 sensor 1, and bank 2 sensor 1. Both had carbon on them not alot but a light blanketing. Also, had a cylinder number 2 misfire code. I pulled the two plugs on that cylinder and both plugs showed signs of carbon fouling, light but nonetheless fouled. Thanks for your interest and help. Jack

 

Hi Jack,

Ok, that model doesn't have a start injector, but the problem is still the same, too much fuel or not enough air. That engine is tougher to diagnose at home.

You changed the EGR, that was logical.
You made sure the EGR tube was clear, good.
Is the air filter clean?
Did you do a leak-down test on the two vacuum actuators on the front of the engine?

Lets see if anyone else knows.