SubiSteve

I have a '03 WRX Sedan bought with 110,000 miles. The Dealer I bought it from did the Timing Belt when I bought it and replaced a coil pack because I said I wasn't going to buy it with a CEL. So they fudged the timing belt job and before it went on the truck to be delivered it advanced timing and the motor was toast.

Luckily since it happened on the dealer's property pre delivery they had to cover it.

Fast forward a week after I physically received the car. CEL comes on.

First I changed to the Cobb SF Intake because they had a crap Advance Auto intake that was cracked. Idled terrible.
The Cobb intake fixed the idle problem and dying out issue from a stop.
CEL remained so I replaced the plugs with NGK Iridiums. The originals were pretty nasty. When changing these I inspected the coil packs and they were in pretty bad shape and it was obvious that dealer didn't replace any. Car started and had a better powerband (when it wasn't showing signs of the hesitation.) with the new plugs. Still a hesitation and CEL.
Ordered a AP V3. Read the codes and was getting P0171- Lean Bank 1 and always a misfire in cylinder 1 and 3 and randomly it would add cylinder 4 and even sometimes all 4.
When in economy mode it took hours for the CEL to come on and I could only ever get the Bank 1 Lean. Never a misfire. I live in Frederick, MD now and recently drove it back to my hometown, Chicago, IL. And drove it back and I got 26mpg and never a misfire with the economy map, just the Bank 1 Lean. With Stage 1 93 Octane I would get the misfires and leans always.

I then put in a new PCV valve and nothing.

After that I bought the Mishimoto Intercooler Hose Kit, silicone vacuum lines, and the stock BPV to replace a ****ty BOV which was leaking. Thought that would do it. Runs better but still hesitates and bucks and backfires and still CEL.

Yesterday I bought a Grounding Kit and the front O2 Sensor as a last resort before I take it somewhere. After work today, about two hours ago I decide to clean the MAF, like I've already done 5 times. As I was shining a light into the sensor housing to get a good look at the two resistors I decided to clean them with a Q-Tip, after spraying it with CRC MAF Cleaner. What do you know there was a huge hunk of crap on one of the resistors. I always thought one was a lot bigger. Nope!

After that she runs perfect. It's only been a couple hours but no CEL yet.

One thing I should point out is when in Neutral I would punch the gas and it would struggle to get to 3k and once passed it would climb normally. Look at the MAF gauge on my AP and even it 5th WOT I could only get as high as 71g/s. Now, in 2nd about 50% throttle I'm somewhere around 58 g/s and in 3rd I hit 145g/s. All in the Cobb Stage 1 Map. I don't know how I never noticed this before.

So everyone with a hesitation clean your MAF thoroughly. Not the connectors, or the sensor you can see outside the housing. That's the intake temp sensor. It's inside the housing out of sight.

Superusdm

iTrader: (6)

Nice write up. Thanks for sharing. Sounds like you replaced a lot of parts through troubleshooting that likely would've caused long term problems, so there's a positive spin.

SubiSteve

Yeah that's my thought. I like the piece of mind.