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i need help diagnosing a 2005 C230 Kompressor (M271 Engine) that is hard to start and will not idle. It runs ok with reasonable power when the RPMs are over 1500. It dies if you let it idle when cold. Will idle but very rough when warm. Starting requires a shot of stater fluid spray.

It is throwing codes P0171 (lean trim adjust limit) and P0300 (misfire) all the time and occasional throwing codes P0304 (RPM) and P0444 (Evap purge circuit open).

Cold compression test results:
dry: 95-100 PSI all cylinders
wet: approximately 110 PSI all cylinders

Cold cylinder leakdown test shows minimal or no leakage all cylinders.

I have used an inspection camera through the plug hole to inspect the inside of the cylinders and it looks good inside. No signs of cylinder scaring and no signs that the valves are contacted the pistons.

I have removed the valve covers and inspected the timing chain that is tight and most likely replaced. I have also placed cylinder 1 at TDC and observed the timing marks on both camshafts. Although not perfect, the timing error appears to be less than a single link so the valve timing appears to be correct. I ulilized the inspection camera to look at the lower timing chain gear and observed minimal wear.

Just purchased the car, so do not know the history. 140,000 miles. The body/interior indicates the car was well taken care of.

I'm at a loss to explain the low compression with no cylinder leakage? Valve timing? Would the compression test be affected by low boost pressure?

any help is greatly appreciated.

- Roger
 

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The psi # does seem low to me but it is normal on some cars. So I guess try to find what is normal for yours. What's important is the #'s are more or less similar, which yours are. If the cam cam jumps a tooth it'll generally run fine but power will suck.
So my guess is it's not cyl psi or valve timing, but some electronic issue. So I'd think about the normal electronic parts that talk to the computer, like the MAF, MAP, intake air temp and water temp. Without those the computer is running blind. Or the part may not be totally failed and just give the wrong #. It should throw a code but it's not an exact science so they can give no code when bad, a code when nothing is wrong, or some other code altogether. The 171 code could simply mean it cannot adjust to get the fuel mix right make it run right, so one part may be telling the computer it needs less fuel but doesn't. If trying to give less fuel then it may misfire giving you that code. Or it could be something like a bad ign coil causing a misfire which the O2 sensor will see and the computer may think it needs to leans out the mix, but again that only makes things worse. It can frustrating, I know, but what may help is researching common problems for that specific engine, those specific codes on a Mercedes, specifically yours, and see if an OBD2 scanner can tell you other stuff you might not normally notice. You can get one on Amazon for $10 that talks to your phone, and it's worth having. I got the little translucent blue one, and considering I've had about five of them now ranging up to $70, the little $10 is just fine.
So research probs with your engine and hopefully someone more experienced will chime in.
 
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