Idle drops when put into gear
 

For those who read my previous post "bouncing idle" I resolved. Turned out the air sensor was not well connected! However, now there is a smaller problem. Whe the car is ither on "p" or "n" the car idles fine (with a/c on or off), however, when the car is on "d" or "2" "r" etc, the car idles terribly. It seems the idle drops and wants to turn off. Any suggestions? Thanks in advance.:D

What model is your car ?

You probably need the air/fuel mixture and /or idle speed adjusted. Some times if these things are not "bang on", accurate, your idle speed will fluctuate or stall.

AARON ROCHARD

1976 230.4 W115

well i would be checking everything in the electrical dept considering your other problem stem from that. look for broken wires that are arching out since your only having this problem when the car is under a load

Thanks for the quick replies. By the way, It's a 1995 c-280 (W202).

Or what about the gear relay or whatever? I think G-Benz had this problem on his M104... where it would idle fine in gear, but in Reverse it was a rough idle. There is something (a relay?) that knows what gear the car is in (N/P, R or D/3/2).
Maybe GBenz will help us out..... :D ;)

I was thinking some thing like that (a relay). I checked all the vaccum line and ther are connected! I noticed that with the A/C on the problem get worse. Is this problem in:
1. Fuel?
2. Air?
3. Spark?
4. Timing?
5. A combination?
Maybe by identifying this we can get to the problem quicker... Thanks.:p

IMO Its a combination of fuel-mixture and air.

What is the RPM at idle in N or P, and in D?

When the car is on "p" or "n" the idle is arround 7-8. When it is on "d", "r" etc. it's about 4-5 RPM. This realy sucks, everytime I stop at a light I have to swicth to "n" in order to prevent the car from shaking and idle from going back and forth.:confused: Do you guys think its the Mass Air Sensor? The weird thing is the "check engine" light is NOT on!

After further investigation, I realized the reason why the idle is droping it's because one cylinder wants to stop. Now when I stop at a light for a while sometimes, the idle begins to drop and eventualy one cylinder turns off. I have to restart the car and the cylinder is back working! Seems like the computer is doing this? I'm thinking it's eather a bad fuel injector or a coil? Am I going on the right track or totally off? Thanks for your help.:)

How do you know its 1 cyclinder knocking off?

I think it may be a relay issue ...

:confused:

Rough idle or stalling in D or R.
 

Hello Guys,

I have the same problem as described in this threat. I drive a 1993 280E euro without the EGR. When starting cold she will drive fine and fast. The minute she is on operating temp the idle will be very low when coming to a halt and if I don´t put here in N or P she will die on me. The engine will slowly drop in rpm´s and then start to shake as if she is running on only a few cylinders. I have replaced the OVP, fuel pump relay, all cables, sparkplugs and the boots under the coils and, this morning, the air mass meter. It didn´t do didly squat. The problem is still there. I had the Benz dealer read the codes and they told me that the air mass meter was faulty and that is why I replaced it. I agree that it does sound like a relay or a sensor since as soon as I step on the throttle the car runs really smooth and fine. She will only act up on idle. I have an after market cruise built in. This one lets me pull the gas so the engine is out of its idle position at a stand still and the idle is slightly higher then it should be. This seems to work but is a temp measure untill i fix the problem.
I hope that this threat brings an answre so I can be a happy benz driver again.
I will talk to my benz dealer again tomorrow and return his beautifull air mass sensor.

Thanks and happy motoring,

Marc

The symptoms do sound like MAS failure. CE light not on? Kinda weird. Do the OBDI cars have that "connection?"

Bad idle
 

Hey there Black mercedes,

The european cars do not show this on the stop engine light. We do not have the strict CA emission laws that make it ,a°°mandatory.

The symptoms are bad enough to get you to a garage realy fast.

After exchangind the meter for the second time the error code is still there. I asked the shop to check for a bad wire from the meter to the ECU since three failing meters it a little too much of a coincidence. I will know more tomorrow and will surely post the results in this thread. Lets pray to the gods in Benz heaven that I will finely find the cause so I can enjoy my car again.
Thanks for the reply,

Marc

Stalling idle is finally fixed.
 

Hello All,

I did exchange the spark plugs and all the cables and boots. Didn´t help. Then exchanged the OVP, this helped with the idle problem while cornering. At least so I thought. The stalling and rough vroom vroom idle when cornering in my case was caused by one of the ignition coils not grounding well enough. So every time I cornered it bumped up a little and lost ground. This meant that two cylinders were not firing. The catalyst will smell this and have the computer shut down the injectors on those two cylinders. The engine will then ofcourse stall. While coasting and hitting a bump it would hick up because of the same thing. When the coil falls back into place the injectors will turn back on. If this happends really fast, as in hitting a bump, the shtuuing down and starting up again will sequence so fast that it will feel like a hickup or a misfire. I lifted all three coils and made sure that when reinstalling them they were all firmly in place and I could hear then `click` into place. This solved my problem. The stalling or really rough idle at a standstill in R or D was caused by a broken wire between the air mass sensor and the ECU. I exchanged the meter for a scrapyard one and I still got the same error code on the computer. I then decided to put in a new one and this also did not fix the problem. Then the shop measured the current between the meter and the ECU and there was none. We found the wire broken. snipped it there, reattached both ends with the usuall duck tape and everything worked fine.
So I exchanged:
fuel filter, airfilter, ovp, fuel pump relay, cabled, boots, sparkplugs and the air mass meter just to find out that it was caused by a broken wire. These things are a nightmare. She runs fine now and I do not have to exchange a lot of things for the coming period. If the engine runs normal under4 normal conditions and you have a problem that occurs only now and then I can not imagine the HFM unit to be broken.
A hickup in the back of the car should be fairly easy to trace. There is not much there to hickup. There is the fuel pumps and the exhaust.

An idle surging betwen 500 and 600 rpm´s is, after reading all the posts, normal on these engines. When I stop the idle will fall slightly below what it should be and then pick up fast.
The surging in my case was a broken wire. Maybe you have a wire that is broken but still makes contact because it is inside a harness, maybe you can try to wigle the wire and see what it does to the idle?

Hope this helps in any way, dont by the expensive part yet, with these engines it is usually something silly.

Greetings and good luck,

Marc