As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 2 ENGINE ACCELERATION SEEMED SLOWER THAN NORMAL DURING START CYCLE BEFORE START LEVER WAS MOVED TO IDLE. ENGINE STARTED NORMALLY AFTERWARDS. MAX MOTORING WAS 23.9%. NR 1 ENGINE STARTED NORMALLY. GROUNDED-YES. REMOVED AND REPLACED NR 2 ENGINE START VALVE, REF B737-900 AMM 80-11-03. VERIFIED STARTER CHIP PLUG FREE OF CONTAMINATION. CONDUCTED DRY MOTOR & LEAK CHECK. SIGNIFICANT SYSTEM GROUND VERIFICATION GOOD, REF AMM 71-00-00-800-811-F00.