As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MCP IAS/MACH ADJUSTER KNOB IS INTERMITTENT. ON MULTIPLE OCCASIONS THE CREW WAS UNABLE TO SET THE PROPER SPEED ON THE FIRST COUPLE OF ATTEMPTS BUT THE PROBLEM WOULD CLEAR AND ALLOW PROPER OPERATION. GROUNDED - YES. RMVD AND INSTALLED NEW MCP. PERFORMED SYS OPS TEST AND LLM REQUIRED TESTS. ALL TESTS PASSED. REF B737-900 AMM 22-11-34/401.