Cruise control - speed surge?

Discussion in 'Engine' started by ss201, Mar 23, 2014.

  1. ss201

    ss201 Hardcore MB Enthusiast

    Messages:
    762
    Joined:
    Aug 29, 2009
    Location:
    Near Lancaster UK
    Car:
    190E 2.6 Sportline, W203 320 CDi SE Estate
    I drove my 320 CDI on the motorway yesterday. Set the cruise control for 70mph. Cruise control kicked in, but instead of maintaining a constant smooth speed (as it has always done), it sped up and slowed down by approximately 5-6 kph. I could feel the car surging and slowing, confirmed by watching the digital speedo display (in kph) varying between 107 and 113kph. When altering the speed up or down with the cruise control stalk the car continued to surge/slow, irrespective of the selected speed.

    Can anyone advise what might be causing this, please - and preferably offer a solution?

    Thanks.
     
  2. Dieselman

    Dieselman Banned

    Messages:
    34,206
    Joined:
    Jul 13, 2003
    Car:
    Peugeot 403 Convertible
    Probably one of the reluctor rings on the wheel hub is cracked or rusted way.
     
    1 person likes this.
  3. OP
    OP
    ss201

    ss201 Hardcore MB Enthusiast

    Messages:
    762
    Joined:
    Aug 29, 2009
    Location:
    Near Lancaster UK
    Car:
    190E 2.6 Sportline, W203 320 CDi SE Estate
    I think I may have caused the problem myself.....

    I recently had two front tyres fitted and went for Michelin 225 50 17s, instead of the recommended 225 45 17 (which are fitted on the rear).....on the basis that they would provide a slightly more supple ride than the Uniroyals I replaced (which they do - the ride quality has improved noticeably). My indie suggested that the difference in tyre size twixt front & rear may have confused the cruise control. I think he's right, as this is the first time I can remember using cruise since the tyres were replaced.

    If that's the case, spot the Chump!
     

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