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For some time, I've had a problem with the performance of my Ford Focus 1.6 TDCi (Diesel): when accelerating hard in the 3rd or 4th gear, there was a performance drop and I sometimes had to go off the gas pedal for gas to be registered at all again. The drop was much more severe than a turbo lag.

The strange thing is that after the temperature dropped one night by about 10°C (and has stayed at that level), the problem does no longer exist. I'm completely at a loss as to what could have been the problem. (The lambda sensor should not be sensitive to 10°C changes in ambient temperature, and I don't know what else would be.)

  • So this happens while running through the rev range in a single gear? Or is it only when you shift from 3rd to 4th? – Zaid Aug 21 '15 at 14:59
  • Yes, it happens in the 3rd gear. Normally, I'd kick down and there would be some acceleration. When the problem was there, I'd kick down and there would be a drop in performance until I would get completely off the gas and then slowly accelerate again. – pmf Aug 21 '15 at 15:07
  • Difficult to say, but I'd inspect your throttle cable & linkage to make sure it's not put out of joint when you kick down. – Zaid Aug 21 '15 at 15:44
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Whilst technically a car has more power in colder air because the relative density of colder air is greater and therefore contains more oxygen than warm air, it should not cause the behavior you describe.

It sounds to me like one of the sensors your ECU uses is faulty. My first port of call would be to have a diagnostic scan done which will pinpoint any faults that car has registered and go from there.

  • No error codes (transient or permanent). Sensor might be; there was a problem with the idle regulator due to a loose cable. – pmf Aug 21 '15 at 14:26

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