E-320 SHAKES WITH A HUMMING NOISE WHEN ENGINE IS COLD

[cdarkoh]

I have a 98 E-320 and when the engine is cold especially, in the morning or in cold weather, it starts fine but if I shift the gear to reverse or drive with my leg on the brake, it shakes and makes a humming noise with the dash board, headliner,seats, etc.. also shaking. After, it warms up to about 95 degrees celscius, the noise stops and it rides as if there is no problem. Also, if I shift the gear to neutral, the noise and shaking level reduces. The problem only happens when the engine is cold and I step on the brake with the gear on reverse or drive. However, it drives smooth.
Has anybody experienced this before? Does anyone have an idea of what might be causing this problem? Please help.

[fraceman]

Rather than start my own thread, I will add to yours. I hope you don't mind and you will find this info beneficial :D

I have the same behavior in my 98' E320 as well. I have been reading around and have followed a few of the other recomendations.

I have replaced the CPS (Crank Position Sensor), this improved the response of the motor at speed, and did decrease the roughness at idle some, but did not resolve it.

I have checked the OBD-II codes (free at Autozone) and got - P0141 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)

I have also read here that O2 sensor errors could be a manifestation of the MAF sensor going bad. Seat of the pants is pushing me towards the MAF because of the following reason: The roughness clears as soon as the engine RPM's increase, or the car is put in Park or Neutral

I'm planning on replacing the O2 sensor, but I'm not sure which one is Bank 1 Sensor 2 (I'm assuming it is the Left side on the down pipe). Or should I be replacing them both?

Or Should I be replacing the MAF before I bother with the O2 sensors?

Thanks,
fraceman

[fried_fish]

It seems like you both have the same problem. I would definitely replace the MAF before doing anything. My friend and I worked on his E-320 and he had the same problem. Replacing the MAF solved his problem but he decided to replace the o2 sensors at the same time just incase. Thats my 2 cents.

[cdarkoh]

I just replaced the MAF and it did not fix it. Also the problem has not trigered any code to cause the "check engine" light to come on. I tried to scan it anyway and I had a pending O2 sensor heat circuit malfunction (Bank 2). Let me know the outcome after changing the O2 sensor.
Thanks

[fraceman]

fried_fish - 10/24/2005 2:38 PM

My friend and I worked on his E-320 and he had the same problem. Replacing the MAF solved his problem but he decided to replace the o2 sensors at the same time just incase. Thats my 2 cents.

Update:

Based on this e-mail from fried_fish, and my own suspicion, I decided to do the MAF first.

I have only had a chance to put about 4 miles on the car so far, but there has been an improvement. (The car was already fully warm from a day of driving so I will need to drive it today to surmise fully the effect.) I did notice an increase in the throttle response. The "tip in" is sharper that it had been in the past. I will post more on this in a few hours.

I purchased a Bosch replacement MAF for about $300 out the door at the local supplier. The big plus I thought was that it came with a lifetime guarantee. Replacement took less than 10 minutes. In fact I think I may have spent more time putting away my screwdriver and washing my hands than actually doing the work.

I'll post again soon.
-fraceman

[fraceman]

Update #2

The cold start this morning was rough again. Once the car was back up to full temperature it was running very well. The drivability is smoother than it has been for some time. The throttle is quicker to respond to sublte changes.

Interestingly it appears that the car's running temperature has decreased some. I will continue to monitor this to see if it may just be a weather related change.

However, the core problem remains un-resolved. I stopped by the parts supplier today and picked up both of the primary O2 sensors (left and right down pipe). I will not have a chance to install them until tonight after work. I will post again once I have some results.

Summary of actions thus far:
1) Replace Park Plugs
2) Replace CPS (Crank Position Sensor)
3) Replace MAF (Mass Air Flow) Sensor


-fraceman

[cdarkoh]

Hello Fraceman: Did you experience the humming noise and the shaking when the engine was cold after changing the MAF?

[cdarkoh]

Thanks for the update Fraceman. That is a very good information. It has saved me from purchasing another MAF. A mechanic friend of mine was also suggesting a vacuum leak but could not specify which one it is. Hopefully someone who have had this problem and solved would come to our aid.
Thanks once again.

[lexrex]

It's normal for an engine to run a little bit less smoothly at idle when it's cold. Have you checked your motor mounts?

When the motor mounts are worn, the looseness allows the engine to rock slightly side to side. As RPM increases above idle, the crankshaft torque plants it against one side and the vibration goes away.

Perhaps humming noise is an exhaust rattle resulting from the vibration of the motor?

[cdarkoh]

Hi Lexrex,
It is not just a humming noise but it makes the car's dashboard shake including the air condition vents, headliner,etc..However, this happens only when the engine is cold. When it warms up to about 95 degrees Cel. everything smoothes out.