Hello from Taiwan. My family has a 2003 A3 1.8 (NA, not turbo) with 60000km. While the car has held up pretty well for the most part, it has this rattling problem that got much worse recently.

The engine's rpm tends to jump when idling, resulting in small rattles. This happens occasionally but hasn't been anything serious for many years. The dealership and third party garages can't seem to figure out what's going on.

In the past few days, the issue got worse. After driving for about 15min, the engine doesn't just rattle but shakes with the engine's rpm jumping up and down as if it's choking. However, it doesn't choke itself out. Usually this happens when I am waiting at a traffic light. Not only does the engine shakes, when pulling the car to the side, I realized that the brake pedal becomes really difficult to depress, making braking useless. I was lucky that the car was just rolling slowly.

When this happened (three times in three days), I put the gear in P, pull the e-brake and gave the engine a bit of throttle thinking that it was choking out. However I don't think this does anything for better or worse. The shaking and needle jumping goes on for 5 mins and I decide to try to drive the car to see what happens. The problem went away after another 5 min of driving.

The other day, my mom was driving the car and this happened. However she shut down the engine and both the brake and ignition completely locked up. It came back to normal after a hour.

It's summer here so I don't think cold temp is the issue.

The garage is still checking the car but I just want to see if any of you are familiar with this situation. Thanks a lot!