I have a check engine light w/intermittent restricted performance (restricted performance seems to happen when the vehicle is slowed down at stop lights not normally when it's up to speed), code p0171. Mechanic diagnosed it as a leaking intake manifold gasket but I'm thinking it might be a miss diagnosis. Wouldn't a leaking intake manifold gasket produce both p0171 + p0174 if not an additional code along with them?

Thanks for the help

 

Depends how big the leak is, where it is, and how long you leave it to see if it also flags P0174.

I wouldn't leave it as running lean is a bad idea! Just fix it

 

Yes, having been in this situation, you will get the left bank and/or right bank lean codes (P0171 and P0174). They'll come in at city speeds but will clear after 20 or 30 minutes of hwy driving.


Mark

 

Lean codes left unrepaired will cause the ECU to compensate by enriching the fuel mixture which will eventually lead to catalytic converter overheating and damage/failure. Then there's the extra fuel $$ spent, the washing of oil from the cylinder walls... The larger the air leak, the more fuel added, the quicker the issues arise. Just trying to point out that foot dragging on this repair isn't a good idea.

Just call me little Merry Sunshine. ;-)