I have a 1999 Audi A6 2.8L and I have the following error codes:

P303: Cylinder 3 Misfire
P300: Multiple Misfire
P305: Cylinder 5 Misfire
P1300: Fuel Level Too Low?
P1300: (Two P1300's showed up)
P0411: Secondary Air Pump or Vacuum Lines?


I noticed that there is not a hose connected to my coolant reservoir on the rear back right side (next to where the sensor plugs into the reservoir in the back). I think it's where the coolant overflow hose goes?? (I attached a pic)



The car runs great for the first 5-10 minutes but right when the engine starts getting hot it starts running like crap. The hotter the engine gets the worse it runs. The check engine light will come on usually within about 15-20 minutes but will be off the next morning when I go to start the car. The engine also seems like it's going to stall sometimes when in idle but ONLY if the engine is hot - usually between 210-230 degrees.

I also noticed what's looked to be coolant or maybe even water leaking out from the front passenger side (by the passenger tire) after the engine gets hot.

I changed all of my spark plugs and replaced all 4 oxygen sensors with OEM Bosch within the last 3 months. I've also replaced both coil packs and spark plug wires within the last 2 years along with both valve cover gaskets and the PCV breather hose.

I also cleaned the MAF with the recommended cleaner, replaced the air temp sensor and got a brand new alternator and throttle body within the past year.

Anyone with any suggestions please help, thanks so much!!!

 

98 A6 2.8 Quattro - 170k

I do not have a hose there on the back of the coolant tank, I don't think there is suppose to be a hose there.

I would check the spark plugs on the cylinders that getting misfire codes. What type of spark plugs did you use? I had a misfire and I switched to Bosch +4 spark plugs and that took care of the misfire.

P0411: Secondary Air Pump or Vacuum Lines - I have not been able to get rid of this code on my car. I know there is a vacuum leak somewhere and I have replace many of the 4mm vacuum lines. The code will go away for sometime but then returns. There are some fixes on the forum but none have resolved the code for me permanently yet. Check all of the vacuum lines.

On the coolant leaks, there may be a bad hose. I am working on tracking down the hose on my car that needs to be replaced. coolant leaks for me but in weird intervals. I know the hoses wear out and will need to be replaced as they get soft.

Good luck, these are great cars fun to drive but require lots of TLC.