I just picked up a 01 5 speed a4 AUG 1.8t. The car didn't run when I bought it. Had numerous vag com codes but the ones that were relevant to this situation were 16705 Engine speed sensor (g28) implausible signal and 16396 Bank 1: Camshaft A (Intake): Advance Setpoint not Reached (Over-Retarded). The problem is I replaced the crank sensor with a new one from auto zone (duralast brand) and the car started right up no problem. Started about 5-10 times with no issues then all of a sudden no start again. It will start for a few days then it will not start again. The same check engine lights come back. I clear them each time from the stored codes with vag com. I verified timing belt is dead on, wires to crank sensor have good readings, fuel pump is good, fuel pump relay is good, battery good. I cannot figure out what the problem is. The only things I haven't checked yet are the cam sensor and the ECU itself. The car drives good when it starts. The car would die at random times when driving with the bad crank sensor. With the new sensor it has never died while driving just wont start at times. The only problem ive had when driving is above 3200 rpms the engine is very jerky. Sort of like a misfire but there are no misfires, maf is in spec, etc. I am stumped. Any ideas? Do you think it is b/c I used an autozone crank sensor vs an oem? If anyone has any input I'd appreciate it.. I am at a complete loss.

 

UPDATE: Bought a new oem crankshaft sensor from audi dealer. Put it in fired right up. Drove for about 50 miles no problems at all. Next morning won't fire up. Just cranks and cranks. Got car to start by pushing it down a hill and popping clutch in 1st gear. Drove it home and it starts again when the car is hot. It seems to not want to start once the car has cooled down. If the engine is still hot it will start up again and again. When I got it to start after popping the clutch, the issue of it being unsteady at higher rpms came back. Above 3500rpms or so the rpms will be really jumpy whether under load or just free revving. Same 2 codes keep coming up. 16705 speed sensor implausible signal.. this one comes up as soon as you rev it, and 17072 EM power relay load circuit (j271) open circuit. This one only comes on after I try to start it for a few seconds and it doesn't crank. I took crank sensor out again tested it between pins 2 and 3 and got 950ohms. I cleaned the sensor also. Put it back in and no start. No other codes besides these 2. I'm at a complete loss. I opened ecu and inspected it for any damaged caps or solders. Everything looks fine. Coolant temp readings are right where they should be, battery is in good condition. Someone please give some ideas. I alread bought a new j271 relay, which I doubt will help, but it will be in on tuesday. I don't want to throw $1000's into it just guessing at the problem. And the fact that it only won't start when engine is cold and the fact that it started when popping the clutch, but the only codes I'm getting is for the relay and the crank sensor makes 0 sense to me.

 

UPDATE 2: I'm not sure why I keep updating since no one obviously has any ideas. I replaced the j271 relay and it seems (so far at least) that it will start now whether cold or hot. I took it for a cruise after putting relay in and it still has weird issue above 3200 rpms or so. Rpms are very jumpy and as soon as this happens the 16705 code pops back up on vagcom, no cel though. The code will stay off and not return until I reach the higher rpms and the rpms get jumpy. I also swapped out the cam sensor (g40). Made no difference. The only other issue with the car is the turbo to manifold gasket is bad and has exhaust leak from there.. I doubt this has anything to do with the issue. The 16705 code is also the only one that every shows up. No other codes.