My S4 2.2 turbo seems to not like low temps. With cold intake temps and full throttle from 3000rpm I get a huge jolt as the engine cuts and thn resumes. It would seem that it does not like the high boost (+-1.4 bar). Last night it did it twice and then suddenly from 5000rpm onwards a sudden drop in power. A VAGCOM test showed up halleffect sensor rpblem on the camshaft. It would appear that the cam belt jumped a tooth or two, but this still has to be checked. Can belt tensioner problems on 128000km cause this and if so where do I get them for a reasonable price? Does anybody know why my car would be jolting at low intake temps but not at high temps on the same boost (measured with an external gauge on the intake manifold)

Got the cambelt checked out and everything seems allright there. So how do I test the cam hall sensor? Ant ideas??

@Leon - I have mailed you the Erwin Manual's section on testing the Hall Sender. Also clean the connector with contact cleaner - it might help?

Your problem puzzles me - it sounds like overboost protection but the car did not show any overboost errors? A stab in the dark - it could be a MAF error. Have you cleaned the MAF? Take out the MAF and spray the inside with carb cleaner from a distance a couple of times. Unfortunatly, on your car's version of Motronic, we can't log the MAF readings. It is worth a try in any case.