I have an Audi A6 C5 4.2l. About a month ago I was driving it and began to hear this awful knocking noise as if say, the intake cams were attached at the chain but all caps were off, Imagine the whole cam spinning and jumping around inside... Thats what it SOUNDED like. I immediately pulled over and flat-bedded it home. Pulled codes and bank 2 valve cover. Inital inspection, the valves and cams looked fine. Further inspection revealed the intake cam had jumped one tooth off timing. How!? Not a clue as it was a major B to get it back a tooth and that was with the use of the tensioner tool compressing and giving slack. SO initial though was shoes were broke off causing too much slack hence the jumped tooth... Wrong Put it all back torqued the caps, new gaskets set timing, used cam locking bar.... and all on bank 2 mind you. as that is where the MAJORITY of the noise came and also the cam sprocket was slightly off for the cam bar to sit in its holes., I though I could hear it on bank 1 as well but not enough to pay any attention to that side. Once i put it all back and put a new battery in I fired it up, had slight knocking then the smoothest idle i have ever heard out of my baby :) then i go to back up and take her for a spin, Bam it comes back when revs drop. Pull back in park it and rev a bit again... Smooth idle then on the way back down the revs I get that same chatter.
ALSO If i am to let the engine Idle like normal no load, it starts again after about 5 minutes. out of the blue. Beautiful idle then crap. and the engine runs until i turn it off. Nor does it appear to even have an issue running. Its just that damn noise, no sputtering or rough idling.... I cant figure out why it is so intermittent outside of raising the revs which will prompt the sound as well. So First thought is..... tensioners, right!? Wrong/maybe
Tensioner shoes are on and attached. lifted the tensioner up and cleared a blockage on the oil supply hole coming out of the heads the blockage was up against that small screen on the tensioner. Put that all back and no difference. I then crack open bank 1 valve cover and instantly notice, not as great of a scene in there, not the cams though. All timing appears to be ok on bank 1. What i did notice is that it appears the oiling is not as good on bank 1. cams are a little more worn, not much and the tensioner shoes (on top) are getting grooves in it from the chain. I have not YET lifted up bank1 tensioner to clear the same oil blockage like the other one had. I am assuming it will be just as bad. And after I do that today I will be all out of ideas... I am so frustrated. Please let me know if you have any questions. I am sure i am leaving out something valuable to you. Here are the codes pulled with VAG-COM. Ive also been meaning to go into the measuring blocks to see if maybe, just maybe itl show the duty cycles on the tensioners to see if one is crapping out or both. Some relevant some not.
17530 - Oxygen (Lambda) Sensor Heating; B2 S2 P1122 - 35-00 - Open Circuit
17548 - Oxygen (Lambda) Sensor; B2 S2 P1140 - 35-10 - Internal Resistance too High - Intermittent
17522 - Oxygen (Lambda) Sensor; B1 S2 P1114 - 35-10 - Internal Resistance too High - Intermittent
16544 - Oxygen (Lambda) Sensor B2 S2 P0160 - 35-10 - No Activity - Intermittent
16524 - Oxygen (Lambda) Sensor B1 S2 P0140 - 35-10 - No Activity - Intermittent 16486 - Mass Air Flow Sensor (G70) P0102 - 35-10 - Signal too Low - Intermittent
17930 - Camshaft Adjustment; Bank 2 P1522 - 35-10 - Malfunction
– Intermittent Cam position MECH (1&3 5V REF SIGNAL
17748 - Camshaft Position Sensor (G40) BANK 1/ Engine Speed Sensor (G28) P1340 - 35-00 - Incor. Correlation
18010 - Power Supply Terminal 30 P1602 - 35-10 - Voltage too Low - Intermittent
18032 - MIL Request Signal Active (Check TCM for errors too!) P1624 - 35-00 - Readiness: 0010 0001