Hello - I have an Audi A4, 2005.5 model year with approx 75K miles. Today, after approx 20 non highway driving miles the car began rattling during acceleration and the check engine light came on and was blinking. I pulled over and turned the car off, waited for about 5 minutes then re-started. The check engine light came back on but this time it was not blinking but I was experiencing huge rattling during acceleration. When the acceleration was from stop to about 30 mph it was rattling and getting worse then it would level off and the acceleration would be fine. I would let off the gas, coast and then when I went to accelerate again the rattling began.

As I was headed home anyway and about 3 miles away I decided to go through town and maybe stop at the local garage to ask what the problem could be when I remembered another mechanic told me that this problem sometimes happens when you get bad gas. The last time I filled was with 89, as I usually do 92octane, but have been cutting back as I did not think this would make such a difference. The DIY fix was to pull over, take the gas cap off for a few seconds, replace it and then see what happens. I pulled over, took the gas cap off for a few minutes and replaced it. When I restarted the car it was fine - acceleration seemed normal but the Check Engine light was still on.

I've also noticed over the last few weeks that when I park my car after driving there are metallic pinging noises coming from the muffler (or possible the cat cvtr).

I'm hoping this prob is a quick fix with bad gas / air in the gas and removing and replacing the gas cap did the trick. I'm hoping it's not the cat cvtr as I've no idea what it will cost to repair / replace and I'm due for new brakes, new tires and a timing belt.

Anyone have any ideas as to whether the "gas cap solution" is legit or what I am looking at? THANKS!
CJ

 

I have the same year and model but with 60 K. My light came on this morning on the way to work but without the rattling or loss of power. I have an appointment tomorrow with my mechanic. This is the first time I've ever had any issues with the engine. I'll let you know.

 

My check engine light issue turned out to be my thermostat. They replaced it and the sensors. The parts were cheap but the labor as usual was not. Set me back about $550.

 

The rattling is detonation. The flashing CEL means your car is misfiring. You didn't say what engine you have (which is kind of important) but if it's a turbo, run the highest street octane you can find, every time. The turbo cars need it to control/prevent detonation. There's a warning in the car to use premium fuel and they aren't kidding.