NoviceSubyOwner Posted March 2, 2020 Share Posted March 2, 2020 (edited) Was driving last night and noticed the CEL came on with flashing "cruise" light. Car started idling rough when I came to a complete stop, dropping RPM and shaking the whole car, sounding like its about to die. Made it home by fluttering the gas in neutral at stops. Plugged the code reader in and got 2 codes but both were the same P0171. Figured I would start by running an injector cleaner in the fuel but when I started it today it would idle for 10-15 seconds and then stall. Any ideas on what might be going on here and where is a good place to start? Thanks! Update: First of all, thank you for all the help and suggestions, this site and its users are awesome. So I purchased the MAF sensor cleaner. As I was removing the sensor I noticed the intake hose was loose on the manifold side. previous owner/mechanic must not have fully seated the hose before tightening the fastener and as I was driving down a bumpy dirt road, it shook off. Cleaned the sensor and the filter anyways and buttoned everything up and it no longer stalls when idling at a complete stop. However the car still idles down (when coming to a complete stop) to the point where it shakes and almost sounds like it will stall before reving up again. Any thoughts? I did not check for vacuum leaks or spark plugs/wires... Edited March 3, 2020 by NoviceSubyOwner Update after repair. Link to comment Share on other sites More sharing options...
BoozeRS05 Posted March 3, 2020 Share Posted March 3, 2020 Based on some quick searching, vacuum leak or sensor malfunctioning. Go to google and type in 'Subaru p0171'. Start reading and watching. My guess is turbo inlet or TGV gaskets are leaking badly. EB's Subaru journal - 2005 LegacyGT Wagon & 2014 Forester FB25 (2008 specB - RIP) IG@legacygtliving Link to comment Share on other sites More sharing options...
Pleides Posted March 3, 2020 Share Posted March 3, 2020 Sounds like a simple vacuum leak. Have you changed out the intake filter recently? Maybe an old hose is torn or worn out? Link to comment Share on other sites More sharing options...
apexi Posted March 3, 2020 Share Posted March 3, 2020 I wonder about the age of your spark plugs and wires, and how clean your maf sensor is. Wouldn't hurt to clean the maf sensor wires, pics below https://legacygt.com/forums/showpost.php?p=5838491&postcount=4 Link to comment Share on other sites More sharing options...
Noob2Sub Posted March 10, 2020 Share Posted March 10, 2020 Just finished clearing the same code and rough idle situation on my 05 and the problem was with the blue T. One line disconnected at the manifold and a second cracked line behind the alternator. Before spending money on parts check for a vacuum leak. Check out this thread for some good diagrams of vacuum hose routing. I traces these and inspected u til I found my culprit but remember just because you find one keep going as there could be more. https://legacygt.com/forums/showthread.php/2005-2006-lgt-colored-vacuum-routing-diagram-143225.html Link to comment Share on other sites More sharing options...
ttnio Posted March 10, 2020 Share Posted March 10, 2020 smoke test for your air leak . Link to comment Share on other sites More sharing options...
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