Astra F/mk3, but only because my brother did tune it, and its true, if you tune it, it gets worse, he put an 2.0i Carlton/Omega engine in it, did a chip tuning on it, it ran well first. He also welded an mk4 Astra hood grill to it, put GSi bumpers on it and glued a diffusor and a splitter to it, then resprayed it with an Alfa Romeo effect paint and put some polished 16" Brock B1 on it.
A good Boyracer, right up to the moment, the oilpresure was gone and the crankshaft bent, the engine had an extrem unbalance, it lituarry shaked the windows out of the car, and of cause ran like a tractor.
So he put another c20ne in it, this time an even older one, whith a 135000 mileage before I got it from him.
It wont start everytime i was in a hurry, and broke down, when I driven a couple of times on short distances. Then the Valves became leaky, it had a poor fuel consumption of 20l/100km (about 11mpg). So I had refurbish the cylinderhead, where on other places the wheelarches startet to rust (thru the expensive alfa-romeo pearlmutt paint), so I welded it and resprayed the whole car, same colour. One week later I lost the GFK diffusor which was hotglued to original GSi bumpers.
In essence, it was a big pile of Problems.