My car is very temperamental, when it is cold its fine but as soon as she warms there are times where she struggles to pull of and she has a flat spotuntil about 3500 rpm and then she will start pulling like crazy there are other times where even after she has warmed up she is perfect there is nothing wrong with her tis problem is very intermittent any suggestions as to what this might be, i have already changed the lambda sensor and the mechanic put the car on the computer and the computer said it was the knock sensor and the map sensor is this posible and/or likely if so whereabout is the knock sensor situated? She also becomes very heavy on petrol when this problem occurs, thye engine is a !.6 16v HLX im going crazy cos i dont want to be changing sensors unnecessarily.