Suggestions please. Golf MK3 2.0 AGG engine. First to third all good at and speed or load. Fourth gear, part throttle acceleration and there is hesitation/stuttering. Pedal all down and all is good.
All plugs, cap, leads changed recently. We will remove the plugs and clean but the issue seems too specific to be plugs. Throttle body cleaned but didn’t help. Am I right in thinking it is possible to reset it or something? Need to get a reader to fit and look at codes. Wouldn’t the fuel filter cause an issue more generally. That said it is old so could do with replacing anyway.
I'm inclined to agree about the fuel filter, but if it's old, definitely worth getting a new one in there. Before the fuel pump finally gave up the ghost on my old 16V, it did begin to be selective on when it actually wanted to pump and performance began to take a nosedive - wouldn't rev all the way, stuttering/hesitation which could occur anywhere in the rev. band and pump became noisier.
Worth checking TPS for a dead spot, may not bring a code up. Lean mixture will bring a misfire or surging normally. Poor ignition can show up at lean cruise but can still be smooth at WOT.
You can do a throttle reset on VCDS but only required if idle is at fault which you say is fine. When I had my mk3 AGG I had problems with the ECU relay - used to misfire when hot, cheap enough to rule out. number 30 at position 3, VW number 165 906 381. https://www.heritagepartscentre.com/uk/165906381-relay-for-electronic-control-unit.html Also had a fuel pump die, but that was found to be because of a blocked fuel return line to the FPR and the fuel pressure reading over 6 bar! Good shout on TPS from keith. That will require a throttle body IIRC as tps is part of the body?
