As title. Mine has started drifting slightly, quite randomly. It can go up to 1500rpm. It will drop the instant I apply the brake.

I have a video of the tachometer while it's doing it, I'll upload it tomorrow when I'm on my laptop.

Also, does anyone know, on a duovalve which part tends to go - the solenoid, or the plunger? Because the right side is playing up, and rather than buy a new valve I'd rather experiment and replace the coil.

According to mcreynol in this thread, post #27, "Idle is managed as a closed control loop by the ECU."

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

It's definitely controlled by the ECU; even W124 OM606s idle speed is closed loop controlled, never mind the fully electronic pump on a W210.

I would begin by checking the operation of the throttle pedal position sensor - you'll probably need to plug it into a star tester, and read the live data. Before spending money, though, make sure that the throttle cable hasn't been over adjusted - i.e., make sure the TPS is going right back to idle position with a little slack in the cable when the pedal is at idle position.

I would not call the IFI pump on the 606 "fully electronic." It has an electric rack modulator and shutoff, but that's as far as it goes. Injection timing is still completely mechanical.

>> I would not call the IFI pump on the 606 "fully electronic."

Point taken, but;

a) in comparison with most of the W123s which people are used to, the pump on a W210 OM606 is light years ahead,

b) for an inline pump, I think it's about as electronic as you'll find on an MB car,

c) I meant, and should have made clear, that the injector pump on a W210 is controlled by the driver in a solely electronic way - there isn't even a mechanical accelerator linkage, whereas the W124 OM606 does have electronic idle speed control, but does have a mechanical accelerator linkage.

Despite the pedantry, [which is admirable - I salute you sir!], , my advice still stands, check the TPS via live data.

Your advice does still stand, but it raises an obvious question. Is this particular live datum available via OBD-2, or do you need SDS?

I would be very surprised if a basic scanner could obtain the live data - but, having never tried, I'm not certain. However, I am fairly sure there is more than one independant garage fairly close to P.O.D. who will have a Star diagnostic machine.

p.s., "datum"; take 10 pedantry points, and treat yourself to a banana!

The TPS is one of the items you can monitor from the OBDII so you can see if the switch is staying open or not however we have learned that cars sold on the other side of the pond don't have the OBDII port in many cases so I am not sure this advice is helpful to POD since he is in the UK.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

I have to wonder, since the throttle position sensor is just a potentiometer, if it isn't just dirty.

Maybe I'll spray a second of two of contact cleaner in there. It mostly happens when hot.

These things always come at the same time. My parking brake has just failed on the nearside rear wheel

http://www.youtube.com/watch?v=URCjPU8kwPc

Video will be there in a few minutes. The rev to 2k is me pressing the accelerator, the sharp drops are when I touch the brake.

I wonder if the fact that it drops down when the brake is applied may be some override for the TPS that the CPU initiates to prevent riding the brake.

I've never tried pressing both pedals at the same time whilst driving...have you? Come to think of it, it seems to be what happens sometimes when I try and drive the car up on my ramps. I have a heck of a time trying to get it to move while keeping a foot on the brake pedal.

If that is the case then it could very well be the TPS or linkage to it which is causing the idle problem and the brake action over-rides the signal from the TPS telling the engine to cut down to idle.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Yes, having seen the video, I would check the throttle cable to the TPS is free running, and that the TPS does go back to the idle position properly. Where are the return springs in the mechanism> - is there one at the TPS, and one at the pedal? - Are they OK? Is the pedal free to move on its pivot? With the pedal at idle, is there any free play in the cable?

The electrical detail I'm not sure about is whether these have an idle position switch as part of the sensor, or, whether the ECU learns where idle is by simply monitoring and storing the minimum TPS voltage. If there's a switch, it's easy, if the ECU uses minumum voltage, it's best to read live data. Live data being the best way to see what's going on regardless.

>>brake action over-rides the signal from the TPS telling the engine to cut down to idle.

Yes, dropping to idle is correct behaviour when the brake is pressed. This function itself can be over-ridden by pressing the throttle again - i.e., it only cancels the first application of throttle.

Yes, there is an SPDT switch as part of the TPS. Here is the schematic.





Parrot, if you figure out how to take the TPS apart without damaging it, let me know as I'd like to take mine apart to check the switch. In my TPS, the resistance across pins 3 and 4 does not go all the way to zero when the switch closes. The minimum I read is about 200 ohms and the opening of the switch as TPS goes above idle seems to be flaky -- the resistance bounces around before going to infinity.

Possible dirty contacts? This problem may be related to my problem where the engine occasionally does not respond to the accelerator pedal at very low speeds (parking lot or stop-and-go driving). Since this is an "occasional" problem, I'd rather not wreck this $500 part taking it apart.

Jeremy

Attached Thumbnails

 

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Cable is fine and snag-free - if it wasn't, the idle would immediately return to whatever it thought it should be when I released the brake pedal.

That the resistance increases as more throttle is applied (and with extra heat, obviously the resistance increases anyway) suggests its the TPS that is iffy.

I'll have a closer look at it to see if theres any way I can squirt fluid in there. It only needs a little bit, and the movement of the rotor.