Underboost / P0299 pending / Bonus: Stripped T25 screw
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    1. #1

      Underboost / P0299 pending / Bonus: Stripped T25 screw

      2004 S60R - 6MT (re-posted from R Forum, as not getting any answers there...)

      Odd problem that has just started happening: Under ~1500 RPM in 1st, the engine feels rough when I go to launch. Launch is fine if I get above 1500. 2nd gear will sometimes drop like it's cutting fuel at times. Idle seems normal. 3rd and higher seem fine, not noticing it there.

      I pulled out my scanner, and I've got a pending P0299 - Turbo Underboost. Some research showed me this might be the TCV, so I've cleaned it and checked the lines. No change. Ordered a iPD HD one anyways, as the dealer one is more expensive (and out of stock locally), but it'll be a week or so before I get it.

      Checked the lower charge air pipe coupler (inlet to intercooler) for cracks, but didn't find any. Ordered a new one of those as well for insurance. It's an 04 with the metal pipe, so there isn't a rubber coupler to break at the back.

      The plastic piping from the intercooler outlet to the throttle body appears to be fine. No cracks or holes found in the accordian folds, and all the sensors seem to be sealed tight.

      Wastegate is set properly, checked with pressure gauge. Cracks at 7psi, fully open at 15.

      She's been running fine up until last Friday, when I really noticed it.

      Any other suggestions? (TB cleaning? Bad MAF (Jesus, not again..)? )

      Bonus question: The T25 screw at the front of the engine, that holds the charge air pipe in place? Yeah, some moron either cross threaded it, or put it in with threadlocker... I've broken two bits trying to get it out, and now the head is starting to strip. Anyone know what the thread pitch is if I have to re-tap it? (This makes it really hard to change the plugs... ) I'm going to have to cut a slot in the head and hopefully be able to get it out with the biggest slot screwdriver bit I've got this weekend...

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    3. #2
      Here's the fallout:

      Apparently, old plugs that are worn out to about .40 instead of .28 like they are supposed to can cause this! Glad I ordered plugs in order to do maintenance ahead of time. Replaced the plugs and the charge pipe to intercooler coupler, stutter/rough is gone.

      Threw in the iPD TCV afterwards, and it's cleaned up the shift lurch that has been happening as well. Launches cleaner and pulls better now

      As for the screw, I had to cut it off. Looks like the head/washer fused itself to the intake manifold (probably heat+galvanic corrosion). Once I cut the head off, I smacked the washer with a large screwdriver and hammer combo, then unscrewed the post with a pair of pliers. Replacement was a hex head metric bolt. M5 fine thread, 1.5 long and a 3/16ths fender washer.

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