Ok here we go everyone with the dreaded misfire at idle issue with random misfire code p0300 and 1or 2 other cylinders misfiring too up in the 100plus range ,but runs fine with open throttle ,after partial engine tear down on one car trace cause to light carbon buildup around intake valves ,so since I had two cars in the shop doing the same thing I decided to do a intake system clean using BG product ,searoam works just the same but u will need a shop air pressure cleaning apparatus set at 40psi when hooked up and running ,pull fuel pump 20amp fuse from fuse holder fuse number 28 on the s4 4.2L engine, also you will need to remove the hose clamp from the main fuel line at rail ,so u can fit apparatus hose and clamp and that's if you don't have the correct screw on fitting for fuel rail ,I ran 2 cans of the BG product through the system it took about 15 minutes ,refit fuel rail hose and refit fuse started car gave a few high rev's to push loosen up carbon out through exhaust did a short road test drive came back hook up scan tool to monitor all 8 cylinders and bam no more misfire had car running for 15 minutes still all read zero misfire, problem solved ,so hence no timing chain ,no bad coils but did replace plugs because they all had carbon buildup on all of them coming out ,so I hope my info help a few people looking for help with dreaded misfire issues ,from Audi of Stuart tech here good luck ,one more thing to also check is the vacuum pump and spring loaded lever that operates the manifold internal flap doors for idle and full throttle flap positions check that lever is not stuck in one position and not working via the vacuum pump pulling and pushing arm to open and close settings this will also cause dread misfire pending what position it's stuck in ,again good luck .
Reply With Quote
Bookmarks