My engine was noisy in the morning so I thought i might need a valve adjustment. So i went to my mechanic and had it done. The next morning after about 3-4 minutes, my rpms dropped and the engine cut out. I restarted it but it
did the same thing. After about 10 mins though, this stops happening, but rpms still seem low at times. I went back to have it checked out, says they readjusted some but i still have the same problem. What could be causing this? Everything else seemed fine before I brought it in the first time.

Have 97 civic ex 134,000miles automatic