UK Car Repair: Vaxhuall Astra 1.7tdi - X Reg, astra 1 7tdi, fuel injection system

Question
QUESTION: Hi, I have an Astra with around 140k on the clock. The car feels very sluggish when started - but this changes if you drive at 3000 revs in 5th gear (usually at 80mph) for a few minutes and then I feel the cars injection kicking in - once I'm back on normal roads the car will them perform much quicker and with more power. have you any ideas what this is? I suspect something is sticking and it clears after being run at speed.

ANSWER: Could it be connected to temperature? It is rather unusual if it only happens under these conditions and i'm not sure of what would cause it.  When you say 'Injection kicking in" I wonder what you mean, the fuel injection system has no variances other than the ammount of throttle opening. Is the car supercharged?

---------- FOLLOW-UP ----------

QUESTION: Its not connected to temp, as you can drive the car for hours at 30-40 mph and this doesnt happen.

It only happens when you travel quite fast for around 3 - 4 minutes.

Thanks!

Answer
I have no idea what kind of car this is it is not sold here in the USA.  If it is not turbocharged then I can only imagine that some type of restriction device is fitted to perhaps reduce emmissions at certain speeds/temperature. Perhaps it should be kicking in at lower speeds but isn't. You need to talk to someone who knows the car or buy a repair manual. There are also many on-line chat rooms, you just have to look for them.