Loosing power

[Wahwah]

I have 2006 corsa which as soon as I get to 50mph just looses power doesn't cut out but when I come to slowing down its struggling to stay running and pulling off again is a near death experience every time if I switch the engine off for a second the problem goes and I can pull off no problem and car runs fine until I get to 50 again and the whole thing repeats had new coil pack and lamder sensors done and it's still doing it but diagnostic test is now coming up with nothing

 

[Burnerman]

Two things I'd consider.....first, run the car without the lambda sensor, just to check for a blocked exhaust and then have the fuel pressure checked.
John

 

[Belle427]

If the car has been reasonably well serviced, and the fuel and air filter have been changed recently, two other common issues are the crankshaft position sensor and the maf sensor (mass air flow).
Quite difficult to diagnose this type of fault as it involves a certain amount of guesswork or someone very competent at engine diagnosis.