1999 Chevy Cavalier Crankshaft sensor, CODE P0335

Hi there,

I'm writing about my '99 Chevy Cavalier.

I starting having problems starting it a couple of months ago. It would crank, crank, crank and sometimes start and other times not. When it wouldn't, it would seem to 'reset' itself when I turned the key to the totally off position and wait a second or two. Then it would start right up.
I also got the occasional backfire.

Next the check engine light came on and the speedometer went nuts so I brought it to the shop.
Code P0335 came up and they replaced the crankshaft sensor. That didn't fix the problem and I had to bring it back. They replaced the battery which was testing bad which fixed the speedometer and initially seemed to solve the trouble I'd been having starting the car. The next day, however, the problems returned including the backfiring (speedometer remains fixed). The check engine light is also on and still gives the p0335 code.

I brought it back to my mechanic a third time and he spent a day and a half trying to figure out the problem, to no avail. He said he even swapped the ignition with one from another chevy cavalier to eliminate that as the problem. Ultimately, he was stumped and referred me to the dealer.

The dealer has been trying to diagnose the problem now for 2 days and $400, but they have no answer yet and I'm still waiting. The only thing they know for sure is that I have a P0335 code and that there is a possibility that the crankshaft sensor is broken again even though it was replaced 2 weeks ago. They re-flashed the computer and that also didn't solve the problem.

Does anyone know what the problem might be?