Hi guys, not sure if you will be able to help but my mk4 hasn't been running great for a while and I've gotten to the stage where i need to sort it out! I just bought a DMS mapped ECU for it, but has had the problem before i put the mapped ECU on it. Its running standard exhaust/cat/intercooler with a 130PD N75 valve, 130 MAF (think theyre the same as the 115 anyway) 130 alloy intake pipe and airbox and i removed the N18 and the other valve (EGR and ASV) and all the vacuum hoses. I'll post the vagcom graph up later but i logged group 11 and my actual boost follows the N75, which underboosts til 2k~ then overboosts so the N75 hit 65% and says cut the boost, then it underboosts and N75 reards 25% and says boost. you get the idea its like a sine wave! Specified boost is 2090mb and the actual boost reaches 2250mb then drops to around 1800mb and repeats. I checked all the vacuum hoses for leaks, the actuator moves freely and holds in place and i cant move the actuator any further than it moves under vacuum so i've ruled out sticky vains and vacuum leaks/actuator. The MAF reads pretty good (up to around 790 full throttle). I plumbed in a temporary vacuum guage so i can see whats happening while driving and it sits around 26" on idle and when i put my foot down it goes down to around 8-9" but backs off when the N75 detects the overboost. It seems to drop from 26" as soon as i put my foot down rather than at a certain rpm which confuses me as there must be an optimum RPM for the vains to open/close? Also, it's clean as a whislte. No smoke whatsoever so it cant be boost leak and it should smoke somewhat as it's mapped. I think it could be a dodgey N75 but that sounds too easy. I took the EGR off and although oily as expected it wasn't coked up (i drive the golf hard most of the time to keep her clean) so dont think its overboosting due to inlet manifold/egr blockage. Any ideas guys?
Sounds like a bad maf to me, can you log these with vagcom over a 3rd gear Wide Open Throttle acceleration (WOT) from 1500RPM to redline. Preferably up a slight hill 001+003+004 (log three at once) 008+011 (log two at once)
