Symptoms: At times, symptoms for major defects can be difficult to notice. In this case the customer could only make out a slight judder while accelerating slowly. There was also an additional noise coming from the turbo (called backspin noise or flutter), but that is not at all uncommon for this type of engine. It was this coupled with a slight drop in power that raised the question mark.

Diagnosis: Modern diesels have swirl flaps in the intake manifold. Due to age and mileage, carbon soot deposits cover these flaps. Add to that normal engine vibrations and it’s no wonder these flaps eventually come apart and break.

Once broken, these bits of metal get sucked into the engine causing damage to the valves and pistons. If you are lucky, they get spat out through the exhaust ports, straight into the turbo’s exhaust impeller, causing significant damage.

Solution: If, like this Insignia, you got “lucky”, the fix means you need to replace the intake manifold and the turbo.

Symptoms: The customer was complaining of power loss throughout the rev range and that the engine would sometimes misfire on start-up.

Diagnosis: We did a brief test ride and checked the ignition system. When we pulled out the coil packs, we found moisture on the coils and that 2 out of 3 spark plugs were loose. So we pulled out the spark plugs and noticed the loose ones were missing the earth electrodes.

Next we checked the engine compression to make sure that the missing electrodes hadn’t caused further damage to the pistons or valves. Luckily, they hadn’t.

Solution: After these checks, we simply replaced all the damaged spark plugs (£15 for all 3). We then torqued them to the right specs to make sure they do not come loose again.

Finally, we put everything back together and, there was a noticeable difference as soon as we got the engine running.