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A healthy reading should be less than 1 / second square at idle (after fully warmed up).

 

Have you tried replacing your sparks plugs and coils? You can swap the coil with another cylinder and see if the misfire follows the coil.

 

Did you just get the car with this problem or the problem just developed recently.

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Yes compression is good on all .All  about 210 psi but  #  6 a little weaker at 195 and plug shows a bit of oil .The codes are p0300 and p0304  . Miss fire clears up at higher rpm  I have not done leak down test 

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In the meantime you may also want to attach a vacuum gauge at the intake vacuum to see if the needle are bouncing. That will tell you something mechanical is bad such as a burnt valve, broken valve spring, bad lifter, etc.

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Excellent. I'm not too familiar with those codes but per the DME 7.8 diagnostic info for 996  P1362 is  intake valve of cylinder #4 does NOT switch to small lift i.e. stuck at large lift. That makes sense because at low rev, the intake valves should use small lift and they change to large lift at higher rev. That's how variocam+ works. You mentioned misfires occur only at low rpm. That's because the lifter #4 is stuck at high lift.

 

P1371 is a general lifter code for any cyl #1-#6 do not switch to small  lift.

 

I think it's time to remove the bank 2 cam cover and inspect all the intake valves.

 

BTW, can you check the "Cam deviation" readings of both banks? Are they solid and remain constant regardless of revs? This does not change the above but I am just curious about the general health of the engine.

Edited by Ahsai
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11 hours ago, wyovino said:

Bore scoring? Cylinder 4 is textbook bore scoring victim for MY2003.

 

While the cylinders may be scored, I doubt bore scoring will trip the very specific intake valve lifter codes.

 

It sucks that one cannot inspect the lifters without removing the cam cover, which involves a lot of labor. That's why the factory manual recommends replacing ALL the lifters (intake and exhaust) of the bank that is affected. The logic is if one lifter went bad, it's possible the others could follow since they wear similarly and are subject to the same operating conditions.

 

If the mileage is high, it will also be a good opportunity to replace the timing chain pads.

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