SZMB

1998 C280 132k mi. The idling is smooth when in P or N and RPM is ~800, but rough idling in D and RPM drops to ~600. Has anyone experienced this problem? Could the problem related to the ICV? Any input is appreciated.

tex07

mass airflow sensor? could be a problem with sensing air/fuel ratio is my guess.

SZMB

Good suggestion. I disconnected the MAF sensor, and the idling is very smooth through all the gears. I'll try to clean it with a can of carburetor cleaner first, and if that doesn't fix the problem, i'll get a new sensor. Have you ever tried to clean the MAF sensor first before buying a new sensor? Thanks for the help.

rfoo

I think cleaning the sensor is possible but you really have to take precaution as it is really sensitive. I read an article here or club202 about how to clean them with care. try researching it.

SZMB

I cleaned the sensor w/ a whole can of MAF cleaner. The idling is a little better, at least the car does shake anymore, but it's still too rough for my liking. I'll go ahead and order the sensor online. The dealer wants $350. The online store autohausaz.com is $185. Not sure if it's OEM part.

ob1kenobi

I agree with cleaning the MAF sensor.

Did you get any cel code? What is it?

SZMB

No fault codes. I just purchased the MAF sensor online, hopefully that will fix the problem.

$tallion

I think its CRC cleaner. Spray it SPray it again if that dont fix it then I dont know what to tell you..you might need a new maf...I Had the same issue this fixed mine

SZMB

I just got a new MAF installed and the idling has improved in Drive gear. However, there's still this low frequency humming sound from the engine, and RPM at 600, and still not as quiet as in P or N. But after driving for about 10 mins and the car is warmed up, idling is very smooth in any gear. Has anyone experienced this problem, i.e. idling becomes very smooth after the car is warmed up?

egreckis

I have the rough idle at 600 rpm until it warms up and the runs smooth after that. Where is the MAF located??

rfoo

Located after the airbox and before the cross intake pipe. It's a round thing with a plug connected on top.

egreckis

Thanks I found the MAF as well as the Overvoltage Protection Relay Module. From what I can visually see the MAF seems clean. So I am not sure if it is bad.. The relay I think is my main problem so I will see if I can acquire thru a mechanic I know. Thanks for the all the help..

bagelsjustbagel

i have the exact same thing. the car kinda rumbles but rpms stay around 600?

New motor mounts will probably fix that

rfoo

I had a similar problem which I thought got fix when I cleaned my spark plug and connecting wires. It went away after awhile but came back just recently. Changed the motor mounts thinking it was the problem but didn't help.

Mine shakes at idle mildly...

But then again it's a case to case basis. It might work for you but not mine. I suspected my MAF so I'll probably clean it and see what happens.

wesrick

So, can someone explain how to 'clean' the MAF?

Pics are OK!

egreckis

I found the overvoltage module at a local MB repair shop and it did the trick. Runs normal now. The guy said when I asked him for the part "yep pretty common to hear that they go out." Now it runs smooth again. It cost $65.00.

ll1l2l1l2lll

this recently happened to me. however it only rumbles at idle. when i put on the gas, it just stops and runs normallly (however sometimes without a lot of power) happened driving on the freeway with a lot of traffic. motor got pretty hot. mine rumbles like crazy though.

egreckis

Okay.. Turns out the overvoltage module was not the problem. The MAF was the problem. Got a hold of one in local parts shop. Cost $210.00. Ran the car for about 100 mi. and had no issues whatsoever. So that must have the whole problem..

g3llings

I'm hoping a new MAF will solve my problem. My car runs so rough right now that as soon as I switch to drive it almost stalls... and if I hit the accelerator it gets even worse. Makes sense to me... If I am already running lean and open the throttle body to let in more air without the MAF recognizing it im going to stall or very close to it.

g3llings

update:

I had the coil pack which controls cylinders 1 and 6 replaced. My car will actually run now, but the rpm's still drop to around 600rpm when I shift into reverse or drive, and I still have a slight misfire... I disconnected the MAF sensor and the car seems to run a little better, but not perfect... does this mean the MAF is the problem, or could it also be the overvoltage relay or Throttle Position Sensor since removing the MAF doesn't totally solve the problem? Seems like it could still run a little rough since the computer then has no read at all of the air flow, right?

egreckis

ad the coil pack which controls cylinders 1 and 6 replaced. My car will actually run now, but the rpm's still drop to around 600rpm when I shift into reverse or drive, and I still have a slight misfire... I disconnected the MAF sensor and the car seems to run a little better, but not perfect... does this mean the MAF is the problem, or could it also be the overvoltage relay or Throttle Position Sensor since removing the MAF doesn't totally solve the problem? Seems like it could still run a little rough since the computer then has no read at all of the air flow, right?[/quote]

I had the same issue and disconnecting the MAF did the same thing. After replacing it, it ran normal. Your problem sounds like the same thing. Shop the unit as the price seems to run quite a range. I've seen on ebay for as low as $45.00 but I bought at a parts shop for $165.00. Need is a costly thing.

g3llings

Thats true. Unfortunately the dealership tells me that the problem is the wiring harness, but maybe I'll get lucky and a new MAF will fix it? The dealers are always trying to get the most money possible. Thanks

wesrick

I found the MAF cleaner at my local parts store - used about half a can on it, but still rougher than a skunk.

I know I need to replace at least one of the O2 sensors - could that be causing a rough idle?

egreckis

Got a check engine light. Buddy loaned me his OBD to see what code would come up. It was P0505 idle control system malfunction. Seems pretty common but the repair not that easy. Need to check several items for correct settings or replace. So I am going to attempt to test any suggestions?

egreckis

I have replaced both the MAF and the overvoltage modules... I still got a check engine code P090505 turns out that could include vacuum leaks.. So I followed a couple of the vacuum lines and indeed found one brittle one I replaced. The idle than kicked up to 750 rpms, but is not consistent so I will be looking to replace as many plastic vacuum lines as it takes to see if my problem is solved.. My car ran about like yours when I disconnected the MAF so you may be experiencing the same anomaly as I am..