Yet another weird question....

[Biggles1957]

W169 2006 Auto. The car has always idled nice and steady at an indicated 700rpm or thereabouts. Today, started up fine and drove - as usual - nicely. First time I stopped at a junction it idled at 100 to 1100 rpm. Drove off - all seemed normal. Every time I stopped, revs settled at about 1000rpm. Stopped for diesel. Started engine, normal idle speed of around 700 rpm. Drove away and at first junction, settled to 1000rpm. On parking up at home, revved engine and it settled every time to 1000rpm. Switched off and came in for lunch. Decided throttle linkage must need a bit of lubrication (My other cars range from 1932 to 1992 so have proper engines etc - none of this new fangled witchcraft / electrickery). Lifted the bonnet and decided it didn't have a throttle linkage to be lubricated or at least if it does its not accessible! Started car, idled at 700rpm. Revved engine, idled at 1000. Revved engine again - and it idled at 700 again and continued to do so every time I revved it. Any ideas chums? Is it going to be a 'module' or sensor somewhere that is on the way out? Any pointers gratefully received!

 

[Craiglxviii]

Throttle position sensor at a guess, these are usually built into the accelerator pedal. Mine went, required a new pedal, £25 off eBay, and one bolt to undo to replace it.

 

[Biggles1957]

Thanks Craig! That's pointed me in the right direction hopefully. I presume there's an actuator at the engine end is there? Or is it all controlled electronically at the point of injection? Just thought it might be worth lubricating whatever mechanism there might be?

 

[Biggles1957]

Anyone know if the pedal assembly (with the sensor built in by the looks of it) is the same for petrol and Diesel engine cars? As Craig says above - loads on eBay but just wanted to be sure before ordering one. Many thanks as always.

 

[Craiglxviii]

Thanks Craig! That's pointed me in the right direction hopefully. I presume there's an actuator at the engine end is there? Or is it all controlled electronically at the point of injection? Just thought it might be worth lubricating whatever mechanism there might be?

All fully electronic.

 

[Craiglxviii]

Anyone know if the pedal assembly (with the sensor built in by the looks of it) is the same for petrol and Diesel engine cars? As Craig says above - loads on eBay but just wanted to be sure before ordering one. Many thanks as always.

We would need to be sure of the part number first, but before that would need proper fault finding via Star to be carried out to ensure that this is the root cause.

 

[Biggles1957]

Well wot a rotten swizz! You can't buy the bit that's broken (the actual sensor) you have to buy a whole new pedal assembly at almost £150!! I would have much preferred to fit a new sensor (there's nothing wrong with the pedal - the car has only done about 55,000 miles and the sensor is held on by two little screws) but will have to get a second hand unit. Taking it off and cleaning it made it work fine for a while but it's gone wrong again today - unless it's something to do with the heat? Anyway, second hand unit on order so...

 

[V6Matty]

Wouldn’t be surprised if the car is working harder in the heat and upping the idle to compensate, maybe wait until it cools down a bit and see if it does the same

 

[Biggles1957]

I thought about the air-con 'drain' but turning that off makes no difference to the problem.

 

[Craiglxviii]

Well wot a rotten swizz! You can't buy the bit that's broken (the actual sensor) you have to buy a whole new pedal assembly at almost £150!! I would have much preferred to fit a new sensor (there's nothing wrong with the pedal - the car has only done about 55,000 miles and the sensor is held on by two little screws) but will have to get a second hand unit. Taking it off and cleaning it made it work fine for a while but it's gone wrong again today - unless it's something to do with the heat? Anyway, second hand unit on order so...

MB pedals that I have seen (in fact, all German cars) have two sensors built in (the car takes the sum RMS value from both sensors).

Most Japanese cars have a metal pedal assembly with a sensor bolted on. Sensor is cheaper to replace, but pedal is way more expensive to start with.

 

[Biggles1957]

Nope - this one (and it's the same as on the W245 B Class I think) definitely only has the one sensor fitted - unless within the sensor itself there are in fact two gizmos?

 

[Craiglxviii]

Nope - this one (and it's the same as on the W245 B Class I think) definitely only has the one sensor fitted - unless within the sensor itself there are in fact two gizmos?

More than likely. My 215 has a pedal assembly with one simple 3- pin lead plugging into the body harness. However inside the pedal assembly there are two separate sensors. That’s in a 2000 model year car.

A few years ago I had the chance to work in the engineering development of the A Class W176. The accelerator pedal in that car has the same sensor architecture in a slightly different pedal configuration.

 

[sonic]

I would leave it for a while & see what happens, not a major issue.