Hey everyone, I really need some help. After a few weeks of troubleshooting on and off, I can't seem to figure out the cause of my stumbling idle. Here are the facts laid out at organized as possible, let me know if I am missing any information. Thanks in advance for the help!
2007 Forester XT Sports (~180,000 kms) with the following modifications;
- VF43 STi Turbo
- Cobb Catted DP
- Invidia Q300 exhaust
- STi TMIC
- Torque Solutions fuel rail with parallel fuel lines
- Cobb AP3 with the OTS stage 3 tune
- Secondary Air Pump Delete
- Koyo Radiator
- Mishimoto Turbo Inlet
- Grimspeed Intercooler Hose
- Light weight flywheel
- NGK Irdium spark plugs
Symptoms;
- P0171 - lean code
- P030-1/2/3/4 - respective cylinder misfire codes
- Stumbling idle (1000rpm to stalling)
- No hesitation under boost or during any throttle
Background;
Has been running great for the past year-ish. I did a road trip to BC, where they had no 94 octane gas, so I was forced to run 91 with octane booster. Once I reached Calgary and hit a red light, the idle felt a bit stumbly and it immediately threw a P0171 lean code.
Attempts at fixing;
- Front O2 Sensor
- Rear O2 Sensor
- HKS Air Filter
- Brand new DENSO MAF
- Checked for vacuum leaks using a boost leak tester
- Ran a few tanks of gas with fuel injector cleaner
After I swapped the MAF, and reset the ECU, the car would barely start. Once it did the RPM's would continually jump from 1000rpm (kind of stumbling) to 2000rpm. I only left it on for a few minutes just in case something was terribly wrong, so that's as far as I've gotten.
Further possible fixes;
- Fuel pump & filter - clogged maybe? I was planning to swap this for a Walboro 255 anyways
- Broken PCV Valve assembly - when I pulled my manifold, I noticed it was pretty gunky; I've already ordered a new one.
- Malfunctioning throttle body - I'll clean this as well as look for any faulty hoses
I can't really think of anything else. Started this thread to document my woes, and hopefully, someone can chime in and I can get back on the road! Luckily, I'm not dependent on my car nowadays, but I'm in Fort McMurray and unsure of any trustworthy shops as a last resort.
Tomorrow I may let the car idle, in hopes that it was just relearning the idle with the new MAF, but I wanted to get some feedback before potentially causing more damage.
My hopes are to get it nice and reliable (again) before putting it under the hot knife for a new paint job, then either build out a brand new short block, or cry of bankruptcy.
Thanks in advance for any assistance.
