P0171 Ford - Mercury cougar 2002 what do i try now ?

Question

It threw this code  I have changed the fuel filter,cleaned the Maf sensor,cabin air filter. What should I do next. I cleared the code and it stayed off but came back on a couple of days later

Answer 1

P0171 Fuel trim lean Bank 1

Vacuum leak are what you have to look for, The fuel trim are most affected when the engine is at idle, and this is where the code for lean fuel trim are usually affect the fuel trim.  You should also do a KOER (key on engine running) test this would also help to locate the problem if one of the solenoid is causing the problem such as the purge valve,

​ Use spray such as brake cleaner to look for the vacuum , such as behind the intake , especially at the PCV hose which tends to rupture.