Hey everyone this is my first post on here. Was hoping you guys could shed some light on my check engine issues. Ive got codes P0171 and P0174 - fuel trim system lean banks 1 & 2, P0420 catalyst sys low effeciency bank 1, and P0507 high idle speed. It previously had a vacuum leak (and P0171/174) with a dime sized hole in the hose between the pcv and manifold, i fixed that and no issues for about a week. I was doing some spirited driving when the damn light popped back on again with all these codes. It idles just fine however it does seem to have a spark knock or slight miss at low rpm. Anyone seen this before? Any help would be greatly appreciated!

 

Since it's only been a week since you repaired the vacuum leak any chance 171/174/507 are just history codes? P0420 might be the current code? I'd reset the PCM manually to clear everything and drive it for a while and see what happens. Just an idea...and welcome to the board.

 

I had the previous codes cleared so there shouldn't have been any dtc history before the new codes. I also checked the spark plug wires and they all looked fine to me, just replaced the plugs 6 months ago.

 

has anyone had any experience with anything like this?

 

I'd still try resetting the PCM, most codes stay in history for 40 ignition cycles. Won't hurt to try....

 

Try cleaning the MAF with some contact cleaner. I've had those codes on my Z and truck (171/174). Fixed the truck by changing some intake spacer gaskets that were leaky and on the Z it was a combination of a dirty and ported MAF not measuring as much air as was going in the engine - previous owner's version of a poor man's tune I guess... just hope they didn't spray it lean like that but nothing I can do about it now. Replaced the ported MAF with stock and lean codes are gone.

I have the catalyst efficiency code as well but that's because of my headers. If you're stock I think GM extended the warranty on the cats but who know if they'll honor it now that they're bankrupt.