w202-erratic cruise control

[Mister T]

Hi all
I am a new member looking for some advice. I set my cruise at 70mph/just under 3K revs. Occasionally when I touch the accelerator the rev counter jumps up to 3500k but the speed does not change.When I tap the brake to cancel cruise control it goes back to normal. Can anyone offer any advice or has anyone had this experience before?

Thanks in advance

w202/1999/1.8C Class/petrol

 

[carabind]

is it an auto? If so, sound like you're dropping a gear when youtouch the accelerator. I had similar with a lexus a few years ago, but this would drop a gear whislt just driving along in criuse. Only way I knew was the rev counter, as the V8 was that quiet! never did get it sorted, though

 

[Mister T]

Thanks

yes it is an auto, I think you have a point, it does sound like it has dropped a gear suddenly. I am wondering if it is connected to the kick down linkage in some way.

Do you think they may be connected?

 

[Paul_Churchill]

This sounds quite normal - its an auto! it has a fluid coupling not a clutch like a manual transmission, its not a solid coupling - when you engage cruise, it gets its ref speed from the pulse rate of the hall sensor in the speedo and thereafter it moves the throttle to maintain the same pulse rate from the hall sensor - it only drops out if you touch the brake pedal i.e it drops out when the brake light switch makes OR if you disengage via the control stalk. If you press the accelerator when cruise is engaged e.g. to overtake on a motorway then the cruise lets you and, when you release the accelerator, it lets the speed fall back down to the reference speed that you set (this is explained in the owners handbook). Cruise is not connected to kick-down or gear change - it is only offered as an option on an auto - if its set at 70mph and re-engaged at say 25mph it simply opens the throttle and keeps it there until the hall sensor is pulsing at the reference that it sampled when you last set it - it cannot change gear for you - but the auto box can and does! that's why its not offered on a manual - it would be screaming in second gear trying to get to 70 with the throttle fully open. Many other manufacturers Cruise Controls drop out if you touch any pedal and they offer cruise on a manual BUT advise that you only engage in top gear - Cruise is only really appropriate for an auto and hence Mercedes never used to offer it as an option on a manual and probably still don't.