JBLUR

07 Is250 with around 103k miles have been driving great with no issues for the past 4 years. Just had new spark plugs installed basic maintenance performed. For a few weeks now the check vsc has come up along with check engine and the other usual warnings. This has caused lose of power and acceleration as I'm aware of past posts about check vsc and effects. Had it taken to a mechanic again and they couldn't find any readings or anything out the ordinary that would cause my symptoms based on the codes that were found. He suggested it could be the ignition coils but he didn't want to replace something that might not be the official issue as mine were still testing as good. also MAF sensor reading and O2 sensor was fine however one was reading a little slower than the other. Any help would be appreciated based on past experiences . Attached are the codes

MikeFig82

iTrader: (13)

If your mechanic tested the rear 02 sensor. I would replace it if it's being lazy to read. Probably ready to just give out pretty soon.

That's the code you have currently. Then go from there if the problems persists.

Did your mechanic test for Vac leaks anywhere?

JBLUR

yes he is, tested brake booster for vacuum leaks and booster holds vacuum as well leaks on the intake using the smoke machine, no leaks found. ( just typing from the inspection notes)

leoferus

P0171 can be caused by misfiring cylinders. Air fuel ratio is 14.7 parts air to 1 part fuel. So, when there's a misfire, the bank goes MEGA lean. In this case, this makes sense due to the fact that only one bank is misfiring and it is that bank that is going lean. If this were my vehicle or in my shop I'd look at freeze frame data for these codes to try to determine when the malfunction is occurring. I'd put the P0171 and P0138 on hold until the misfire is resolved.

For your misfire issue, if it were in my shop I'd look at freeze frame data and learn when the malfunction occurs. Sometimes, the code that has freeze frame data pertains to the coil that caused the misfire. If you can't look at freeze frame then, I suppose, you could drive around with a scanner connected and see if there's one cylinder that sets a code before the other. Try swapping the coil with one from the other bank, etc. Good luck.

Curious. Were Denso spark plugs used to replace the ones that were removed?

JBLUR

Yes Denso spark plugs were used for replacement and yes Mechanic drove for around 20 miles with the computer connected and all of the readings were normal and my car didn't malfunction during this time as I have been experiencing so the exact issues couldn't be pinpointed to a particular part due to this. Always seems to be the case your car acts fine the one time you want it to mess up in order to indicate what the issue might be while the mechanic is actually driving it around.