I have a 54 plate vectra which has chip box installed, it jerks at times at the rev range of 1500-2500 rev (95% of the time it jerks at 2000 revs) I have done around 20,000 miles in this car in a year of owning it and has been perfect.
Recently it started to go on limp mode a lot and after checking, it left me a deep hole in the pocket due to changing inlet Manifold, EGR valve and throttle body to solve the problem. Manifold and EGR valve are brand new and from Vauxhall, whereas throttle body is second hand from a vauxhall breaker. Throttle body was changed after all the manifold and egr valve job as it was still going on limp mode.
Now that limp mode problem is solved, it still jerks at times. Sound like turbo as it sound like sequentional dump-valve noise (kushhh kusshhh kussshh) and you can feel the jerking too. Car does not lose any power what so ever and pulls really hard at any revs like it should, just jerks.
What could be the problem? It doesn't happen all the time, just say about 1/5 times when you are at that rev range.
Thank you in advance :-)