ALL SHOOK UP
QI have a 1993 Rover 214 Cabriolet. At idle there is a vibration that is felt in the cabin and the steering wheel visibly shakes until you rest your hand on it. One of the electronics modules next to the battery shakes at idle – but increase the revs slightly and it stops. The engine looks rocksteady and the mounts are in good order. Do you think it’s just cabriolet ‘scuttle shake’? Would suspension braces help? John Jeffrey, cambridge
AWe don’t think this is directly related to the car’s open body – and suspension braces would have no effect. We think you’re experiencing a simple resonance. The engine’s producing a vibration that may be too fast to notice, but a lower-frequency part of it (a ‘harmonic’) is being picked up and amplified by part of the body.
Try recalibrating the idle speed. Turn the ignition on with the engine stopped, then press the throttle to the floor and release it five times in succession. Wait a couple of seconds and you should hear the stepper motor that controls idle speed reset. It’ll then fine-tune itself as you drive, if it needs to.
If this doesn’t cure it, look for a small air leak, or similar, that’s upsetting low-rpm running. Make sure the Manifold Absolute Pressure (MAP) sensor is firmly attached.