Poor running when cold

My mother’s 2002 Astra G 1.6 is very rough – almost undriveable – from cold start-up until warm. Once warm, it runs fine but cuts out intermittently. Following a diagnostic check by her local mechanic, the crankshaft and camshaft sensors were replaced. This cleared the codes, but the problems persist. Her mechanic has declared that he is at a loss as to what next to look at. The car has done 85,000 miles and covers fewer than 3000 a year.

I am not sure whether this is relevant, but around eight years ago we experienced the same cutting-out problem, but not the cold rough running. The problem was traced to the EGR valve and was solved by blanking it off.

Chris Robertshaw

With any temperature-related problems, the first check should always be the coolant temperature sensor. Using live data to ascertain if this is reading correctly would be a good move. If the sensor is reading accurately then next check would be the air temperature sensor. This is located in the induction hose on your mother’s Astra, and a false reading from this could give the symptoms she has.

If both of these sensors are reading accurately and given that the original codes were for the crankshaft and camshaft sensors, I would check for any play in the timing belt. A slack belt – possibly due to wear in the tensioner or water pump bearings – could give symptoms similar to those experienced.

With regard to the blanked-off EGR valve, this may well be relevant and it would be worth removing the valve and checking the blanking plate, which may have blown through, recreating the original problem.

If none of the above exposes any problems, I would suggest starting with the basics. Carry out a compression test to ensure that one or more cylinders are not lacking compression. The problem may also be either a worn camshaft or hydraulic lifters that are sticking or worn.