W140 - wont go over 2000rpm

[frog1520]

Had a strange problem in my 97 S320 today. Was driving around fine, then when I pushed the accelerator the engine wouldnt rev, and the car was 'stuck' going at exactly 20mph. Taking my foot off the accelerator would cause the car to slow, then if I pressed again, it would go up to 20mph again, but no further - as if it was being electronically limited.

This also happened to me 4 days ago. When it happened last time, I stopped at the next lights, and turned off and on again. Then its been fine for 125 miles.

When it happened today, I pushed the kickdown switch, the box changed down, the car roared into life, and then it was fine. Havent had any problem with it since.

There are no strange noises, no misfires and no gearbox clunks. Temperature and oil pressure are good and the engine is running very smoothly.

Any ideas??

Thanks!

 

[Brian WH]

Sounds like a problem with the ECU mate. Needs to go on a diagnostic computer check at the Dealers I would suggest. They can look back to see what happened.

 

[frog1520]

Sounds like a problem with the ECU mate. Needs to go on a diagnostic computer check at the Dealers I would suggest. They can look back to see what happened.

Brian, thanks for the info mate!!

I wonder if S&R Motors (Mercedes Dr!) would be able to do the diagnostic check? Its easier to get an audience with the pope than an appointment at my local stealers...

 

[Brian WH]

Brian, thanks for the info mate!!

I wonder if S&R Motors (Mercedes Dr!) would be able to do the diagnostic check? Its easier to get an audience with the pope than an appointment at my local stealers...

As long as they have the Diagnostic Kit, anyone can do it.

 

[Anders]

This could sound like a problem with the Tempomat (cruise control) - does yours have Speedtronic, which sets a max speed?

 

[Brian WH]

This could sound like a problem with the Tempomat (cruise control) - does yours have Speedtronic, which sets a max speed?

If it is set to Speed Limiter it would appear on the Speedometer as set to 20mph. I didn't think you could set it that low anyway??

Update
Interesting that I tested mine and it does just work at 20 mph, minimum it will go, and if you kickdown it does override it. So if he had Speed Limiter that could have been the cause.

 

[frog1520]

This could sound like a problem with the Tempomat (cruise control) - does yours have Speedtronic, which sets a max speed?

Theres no speed limiter on this car as far as I know; you cant push the cruise control stalk in, and theres no trip computer under the 'sunglasses' box on the dashboard..

I didnt have cruise on at the time, but was wondering about this myself. I'll get the diagnostics checked out as Brian suggests (thanks), but if it happens again beforehand I'll try and engage cruise and see if i can accelerate it pushing the stalk up...

Strange problem... thanks for all the input, ill let you know what happens!

 

[Brian WH]

See Update above.

 

[markku]

Lim

Theres no speed limiter on this car as far as I know.
I didnt have cruise on at the time, but was wondering about this myself.

There are at least 3 variations of cruise controls in S320 -97
- Plain cruise control
- Speed limiter with variable speed
- Speed limiter with fixed 20 mph (30 km/h) limit

I have the latest and in the beginning (new to Merc) when hitting the blinker I did activate the speed limiter instead. My display says LIM when activated. I nearly got a heart attack by interpreting it as LIMp home mode.

Consult your user manual.

Still cannot figure out the necessity of this function.

 

[frog1520]

There are at least 3 variations of cruise controls in S320 -97
- Plain cruise control
- Speed limiter with variable speed
- Speed limiter with fixed 20 mph (30 km/h) limit

I have the latest and in the beginning (new to Merc) when hitting the blinker I did activate the speed limiter instead. My display says LIM when activated. I nearly got a heart attack by interpreting it as LIMp home mode.

Consult your user manual.

Still cannot figure out the necessity of this function.

Thanks for all the info chaps.

I think this is actually the cause of it, i.e. invoking the speed limiter by accident. I didn't even realise the car had this 'feature'; if I try and activate the cruise below
about 20mph, it instead sets the speed limiter to 20mph; and then wont go off until you either kickdown or deactivate cruise. The manual documents this but suggests
that something will appear on the dashboard to tell you its on. On mine, nothing appears, but its definately on!

I'll just be careful not to hit the cruise stick accidently in the future!

Now, why do they even make a speed limiter with a fixed speed of 20mph? Is that actually useful anywhere? A variable speed limiter I can see a good use for (speed cameras, built up areas, schools etc), but fixed 20mph seems pretty useless to me. Stops you speeding around the car park I suppose....

 

[markku]

Lim

that something will appear on the dashboard to tell you its on. On mine, nothing appears, but its definately on!

Are you sure? The display (LIM) shows up on outside temperature display, which is normally hidden behind the steering wheel.

Correction after testing: LIM shows above odometer very bright.