1990 325i says "vroom vroom vroom" when I start it...

The other day I think I didn't put my gas cap on correctly on my 1990 325i convertible. The idle was rough when it got to 2000 rpms, and I think I rectified the situation when I put some fuel additive into the car. I thought I accidentally put unleaded regular into the car...

After troubleshooting, the car's issue seemed to magically disappear. Whatever the problem was, it has gone away.

The stomp test throws a 1-2-1-1 error code, and I could not find a loose gas cap code, so I associated that code to the gas cap.

Fast forward four days. Problem still gone. Drove the car 100 miles without issue. However, I have now noticed when I start the car sometimes, it says "VROOM VROOM VROOM" about six times, then settles down to 6-800 rpms. I think she goes up to 1000 rpms when it does the vroom thing. It will do it between three and seven times, as if I am revving the motor with the accelerator.

Anyone know what's going on? Like I said, the code is 1-2-1-1.... which is rather vague.

I posted this in your 325es vs. 325i thread, but just to make sure you see it in one or the other, here it is again:

http://www.e30tech.com/forum/showthread.php?t=69067

Similar problem (surging idle), same code, odd outcome.