I have this problem on my 96 Regal custom. 3800 Series II NA. Through an SES at me. Got it scanned. P0171. "Bank 1 lean". There don't appear to be any vacuum hoses leaking. Cleaned MAF with electrical cleaner. Replace MAP. SES went away for a week, then came back while I was in traffic on the highway. Rough starts. Once it starts and is warmed up, I can start and restart with no prob until it cools down. Then rough starts again. What could it be?