amir

Hi, I have an A4 1.8T 2002. My check engine light came on a few weeks ago and after 20 enginge start ups, it went off but came on again soon after! it happened several times. The engine shakes for 10-15 seconds when I start it in the morning (specially when the weather is cold) and the exhaust makes "pop pop pop" sound! last week I took it to dealership and the computer scan detected these codes: 16684, P0300, 16804, P0420 (multiple cylinder misfire and Catalyst system efficiency below threshold) they suggested that it needs tune up. I agreed and they changed the air filter and spark plugs...., but soon after I left It came back on again. Right now I have poured some Seafoam engine treatment to clean the fuel line. I did some research on the internet and got confused! it looks like I have to keep changing parts until it is solved. Please give me your thoughts Thanks!

Dinky_B6

I had a similar problem on my 04 A4, the only difference is that I was getting an EPC light from time to time and I had some misfires while driving. The random or specific cylinder misfires code sometimes mean its the crank sensor(thats the codes I got too). Did you ever have any trouble starting the car so far?

Anyway I've replaced the crank sensor and the car is running smooth and perfectly fine now, thanks to forums and videos no need to take it to a mechanic

ceeeheee

check ignition coils and plugs for misfire. My 01 had a misfire few weeks ago so i just replaced the 4 coils and plugs and runs good again. They are really easy to get to and check, so its worth a shot.

Qbert

One cause many time overlooked. Vaccum problem. Same thing on my car did a complete change of all different relief valves and vaccum. Problem solved. About 300$ of parts at Audi. Engine runs like new.

Gave multiple misfire of cylinder 1-4 and lean mix

Joejohn2412

Hello, I know this is a few years off but hopefully this would help someone. Same thing happened to my 04 1.8. 14 dang codes. Ran like crap idling. Mechanic wanted to replace the head gasket. Came upon this by chance, collapsed breather hose. Found the hose and come to find out my crank case breather hose was demolished also (Hard plastic....very brittle) probably happened when I changed the oil. It comes out of the crank case right under the intake manifold. Replace hoses and pcv, car is running new! More power than before!! Maybe $110
One way i figured this out was I disconnected the bottom breather hose from intake (to pcv) and plugged it with my finger. Car instantly came into it.