Hello everyone, I have a 2002 A4 1.8T Quattro with 102,000 miles. Previous to now the only major problem I had was the computer needed to be replaced which I paid Audi to do a long time ago.

About 15,000+ miles ago I did a timing belt, tensioner, waterpump, drivebelt, etc. replacement myself.

Everything went well, with no problems until just this past week.

My wife was driving the car and the acceleration and idle just started getting jerky on her. She pulled over and we had it towed home.

I tested it out, yes, sure enough the idle is very rough and it's very jerky at 1st & 2nd gear, I didn't bother trying anything higher. The exhaust also smelled of unburnt fuel (the proper term being "lean", correct?).

I pulled the codes and got P0011 and cylinders 2 & 4 misfires.

I'm planning on taking apart the front of the car and taking a look at the timing belt, water pump and tensioner, perhaps something went bad and it's off by a tooth or so.

My questions:

Is that the right approach?
Or is the problem something else?

If so, what's the best method to see if my timing is good?
And if not, how to correct it?

Any help will be appreciated, thank you.

To be more specific:

The P0011 code:

16395 - Bank 1: Camshaft A (Intake): Retard Setpoint not Reached (Over-Advanced)
P0011 - 002 - Lower Limit Exceeded

I also HAD another code:

16804 - Catalyst System: Bank 1: Efficiency Below Threshold