So I purchased a 2000 S4 a couple weeks ago as a daily driver. The car Has 180k Miles, and had the clutch done the day I bought it. Knowing that information Im wondering if any of you may be able to diagnose my problem. The car starts great 90% of the time, but once in a while it wont start at all, it will continue to turn over and not even fire. A remedy for the silution for now is simply roll start the car, It will turn over and never start then Ill roll start it and it will start?? Once it is roll started I can turn the car off and start it normally without any issues (it bassically resets whatever is going on). I have also bee keeping track of when it does it, I noticed that Ill park the car and I have roughly 30 minutes after the car is turned off to restart it and it is fine. After 30 minutes it wont start. If I wait a few hours until the car Is all the way cooled down it will once again start as well. I replaced the coolant temp sensor, swapped coilpacks and the sensors on the air box with my brothers s4 with no luck of fixing the problem. If you have heard of this let me know I could really use the help. Also i apologize if I am posting in the wrong section I have no idea how to navigate the site yet!

 

moved to correct sub forum

 

check all of your wiring from the battery, just to make sure nothing is loose/ broken, etc. check ground wires for both alternator and starter. i'm guessing it's the starter.

 

Could it be the crankshaft position sensor? ECU gets the rpm info from it. Have you checked the error codes?

 

I think that there are some minor fault in battery. please check it.

 

the car cranks amazing, it does not seem dead whatsoever. I have a check engine, the only code that reads is front o2 sensors. Could it be the crank sensor? yes... but wouldnt that mean it would never start even from a roll? Another thing to note is when the clutch was done it received a new battery.

 

I suppose faulty crank sensor would give some error code, so you can exclude that possibility. Based to your info we should concentrate what is different in the normal start and roll start.
This is far taken. Could your spark plugs be wet for some reason. This would explain it won't start but when it starts it starts ok after that. This wouldn't explain why it starts with roll start.
Second idea. Maybe your faulty O2 sensor sends incorrect data to ECU, which mess up the fuel/air relation. Again, this wouldn't explain why it starts with roll start.
Check your battery, in idle state fully charged battery should be something like 14,3V, when starting it should not drop much under 12V

This is just brainstorming but...

 

The ecu isn't opening injectors or sending spark when it has the problem. On a good start up in it at 11.2v while cranking, I have yet to test it when it won't start