1994 E420 runs rough at idle and blinkers
 

Hey everyone, I have a 1994 E420 with the "Check Engine Light" On. It runs great except after the engine warms up when the car runs rough when you come to a red light with the foot on the brake. The RPMs also sometimes flucuate below 500 RPM and the engine runs a little rough when the engine is warm. If I put the transmission in neutral, the RPMs go to 600 RPM and runs smoother. What do you think it is? Since the "Check Engine" light is on, I have a feeling I need an oxygen sensor, but not sure. Also I believe the plugs were changed in January and not a lot of miles put on since then. Also a new air filter was put on recently. It is possible that the wrong plugs are in there, but it seems like it is something else.

Also, when the car warms up, the blinkers sometime don't work. Also the main cig lighter doesn't work. I checked fuse and they appear okay.

Please help.

Matt
1990 E420, 140k miles

I would also like to add that when the engine is warm, have the trans in drive, with foot on the brake, the RPMs can flucuate from 100-500 RPM sometimes. But then when I hit the gas pedal, it's a little okay, especially when I take off after a traffic light turns green.

Has the engine wiring harness been replaced?? If not you need to do that asap. Try not to disturb it too much while you're checking. The problems you describe could be due to it.

If it has, then read the codes (DTCs) stored in the Diag Module; use the procedure in MENU#2 on my pages.

Let us know what you find.

Check the DM codes on the pushbutton / LED of the 8 pin diagnostic connector.

So the plugs were replaced in January...what about the caps and rotors?

btw...check fuses up close and personal...hairline cracks are known for not being spotted at first glance.

Good luck!~

Would like to clean the mass flow sensor
 

The wire harness has been replaced. I would like to take off and clean out the mass flow sensor on my 1994 E420. Can you please tell me where it is located? Does anyone have a diagram of this engine layout?

The MAF is located under the air-cleaner; remove it and then loosen the 'clamp' around the MAF body to remove it. Don't forget the connector on the side of the MAF.

Use some MAF cleaner and re-install. Let us know what happens.
.

How is the wiring that feeds the ETA? Usually that's toast by 140K and can lead to rough idle..

Have you checked for vacuum leaks? I've heard/seen the intake like to leak on occasion.

Jonathan

What is the ETA?

I cleaned the Mass Flow Sensor and no change. My mechanic says I need a new one. I disconnected the Mass Flow Sensor and the bad idle goes away , but the engine wants to stall when I hit the accelerator so I connected the Mass Flow sensor back. The rough idle returned.

I don't think it is a vacuum leak. It gets worse when it rains. My mechanic says that a bad Mass Air Flow sensor will have a harder time with moisture outside.

ETA is electronic throttle actuator. All this guessing is great sport but why not check the fault codes?

My mechanic say that the fault code says it is "fault 90" or something which has no description, is it like a miscellaneous code.

Although there could be a problem with the mass flow sensor, i could not see anything wrong with it with the naked eye. It looked fine to me. I would hate to replace it and still have the same problem.

Where is the ETA? Do you have a picture of it?

The ETA 'saga' I had is described in MENU#24 w/ pictures and links to get it fixed . . . if it's bad.

This is not a credible assertion. There's no substitute for reading the codes yourself.

I've seen a bad ETA throw Odd codes (shorting wires do wonders for DTC's).. Cut the wiring insulation open and have a look..if it's bad it's bad so I wouldn't be to concerned wiggling it about.


As for code checking, I've never seen a 90.....follow Jim's site, build a code reader and go through it step by step..his site is an utter WEALTH of information!!!!

Jonathan