This may be a stupid question, but here it goes. My father in law's sable keeps popping a check engine light with a p0171 code. I replaced the fuel filter, air filter, and cleaned the MAF sensor but it keeps throwing a p0171 code. Please help, it's got me confused. The other thing I know about this car is that the tach flutters around 700-900 rpm's when at idle. I know it's in the zone, but it still is enough to piss me off, due to the CEL coming on, please help.