geniushanbiao

One day my wife told me the check engine light was on my 07 R350 4Matic with about 80k miles. I asked her if there was any driveability change she said no. I got home and hooked up my Autel EU702 scanner and it returned 3 codes: P0300(random misfire), P0303(cyl 3 misfire) and another one about camshaft sensor/actuator on bank 1 I can't remember the exact code number since those codes appear differently on the EU702 scanner. I was very much worried if it was the "soft sprocket" problem but I proceeded with my diagnosis.

First I cleared the code and tried the start the engine. It started fine but after a second or so it started to shake and the check engine was blinking. I shut it off after a few seconds and then hooked the scanner up again to check. This time there was no camshaft code but the P0300 and P0303 were remaining.

Then since it says cyl3 misfire I pulled the coil (of course pulled the air cleaner box as well) and checked the resistance it appeared fine. Then I pulled the plug and it looked fine(I replaced the plugs with the stock Bosch ones around 72k miles mark around a year ago). Then I swapped the cyl3 coil with the cyl6 coil. Put everything back, cleared the code then start the engine it still shakes and check engine light blinks. Shut it off then hooked up scanner it showed me P0300 and P0302(cyl 2 misfire)... Very confused so went to sleep.

The next morning I started working on it again. Since it told me about camshaft sensor I pulled all 4 camshaft sensor wires(didn't remove the sensors) and measured the resistance and all are the same(I don't have specs but I believe they are all in range). Also pulled the 4 actuator wires and measured the resistance all were about 10Ohm so also assume they were working. Put everything back and then tried to start it. It shaked as I expected. Then I turned off the engine and restarted again. Can't believe it went OK! Also the check engine light was OFF! I let it run for some time and did a test drive everything was fine! I stopped the engine and hooked up the scanner the 2 codes were still there. I cleared the code then used the car till today about 70-80 miles passed no problem came up. Looks like a ghost problem that came and go. The only thing I could suspect was that there might be some air in the gas line...

Anyone had similar experience?

need4spd

A lot of electrical gremlins are caused by bad ground connections, I would check those first.

efzauner

Great! So maybe a dirty connector?
I have had similar issues with *brake fluid leak stop driving immediately*
There was nothing wrong, I disconnected the brake level fluid sensor to check it. All was fine. Reconnected and all was fine again. Gremlins!

geniushanbiao

Good thinking! I'll check. Do you think the battery connection can be a problem as well? I never opened the battery well since I bought this car 1.5 years ago.

geniushanbiao

Actually I also have the "top up washer fluid" warning all the time since a couple month ago. Haven't got time to check it up.