lastls1

My theory is that there is a solenoid, ECU controlled, that adjusts the intake cam timing at certain RPMs. It appears that the exhaust cam is directly driven by the timing belt but that the intake side can vary the timing. At idle or below say...1500 RPMS the solenoid is active. Above that the solenoid is inactive and the intake cam is allowed to change timing. Moving the two plastic half moons parts that touch the chain up or down retards or advances the intake timing. Is this about right??

The reason I ask is that at idle, my engine is rough and CEL is on. Above idle, over 1500 RPM, the car drives fine and mileage is in the 18.6 MPG range so things ain't so bad. I think the cam chain tensioner is not adjusting things and is stuck in upper RPM position. CEL codes are misfire cyl 1, 2, 3. One entire bank, which is why I suspect the CCT. Plugs and wires are new.
Thoughts??

4Rings::G2 boosted::

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The tensioner doubles as the variable intake timing actuator. It has two plastic "half moons", one on the top and one on the bottom. In between there's an oil filled piston to keep the tension on the chain. The whole tensioner moves up and down via a solenoid. When it's down there is more chain between the cams on the bottom, thus increasing intake valve timing. When it's up there is more chain between the top of the cams, so the intake timing is retarded. The VVT (variable valve timing) is only active between 1500-4200 RPM and only at WOT(wide open throttle), in that range increasing the intake valve timing causes an overlap with the exhaust valves and creates a suction effect where the leaving exhaust gases help to suck the intake mixture into the cylinder. At lower RPMs there is not enough air velocity for this to work, at higher RPMs the velocity is so great that some of the intake mixture would get sucked out into the exhaust. (This is also why folks with superchargers are disabling VVT, under boost it causes some of the intake boost to be lost to the exhaust).

Now, if one of your VVT actuators wasn't working it would result in cam angle error code, but only if you did several passes within those RPMS with the throttle all the way to the floor. The error is kinda hard to reproduce on demand. The reason for the error is that each cam has a cam angle sensor on the other end of the cam from the actuator that tells the ECU whether the cam is actually being advanced.

Do you get metallic rattling from your valve covers? That might be an indication of a failing tensioner cylinder that's no longer holding oil pressure.

Did you have a timing belt changed recently? It's possible your timing is off on that bank, that would definately result in the misfires from all 3 cylinders. Or your timing belt might have skipped a tooth. Or your intake manifold gasket is torn on that side. Or your loosing cylinder compression on that side, see if you can do compression test on cyl 1,2,3.

lastls1

Compression is good in all cyl. - around 150-190. Timing belt changed at 105K miles. At 153K now. No noise from under valve covers. Engine runs strong up to red line. Just a bit lumpy around idle. My indy mechanic is puzzled as well. His guess is cam timing slip/error.

4Rings::G2 boosted::

my best guess would be a timing belt that's off 1 tooth on that cam or a vacuum leak in the intake manifold on that side. What are the fuel trims reading on this bank?

4Driver4

I'd agree. VAG-COM and/or check cam timing with the tool.