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Cam chain tensioners are about the simplest devices on the planet. I'm always mystified when I hear about them failing or being defective. The tensioner is a spring-loaded ratcheting plunger that applies a steady "push" to the flexible cam chain guide on the back side of the cam chain tunnel. As the cam chain stretches with wear, the spring and plunger on the tensioner press the cam chain gide farther inward so that the cam chain does not become loose and jump off the sprockets. The ratcheting part is what allows a mechanic to retract the plunger so that you can slacken the chain and remove the cams. If the ratcheting mechanism failed, it's possible that the cam chain could slap around in the tunnel under heavy engine loads, and the valve timing could be compromised, with intake and exhaust valves opening and closing at some random deviation from specification. That's a possible cause for the performance and noises you described.
Assuming a second bad cam chain tensioner, they're pretty darn easy to replace... a wrench, a screwdriver, and possibly a special holder tool for installation. I've never used the special holder tool... I just keep a phillips screwdriver engaged on the plunger screw and "palm" it during installation. The labor would be very minimal.
But I would also be concerned that there is something wrong with your cam chain... it may be stretched out of specification. The only way to tell is to take the valve cover off and measure. An excessively stretched cam chain could conceivably lead to early and repeated tensioner failure, or it could be the sole cause of the problem... too stretched for the tensioner to make a difference.
Of course, the problem may not be with the cam chain or tensioner. Lots of stuff can lead to the lurches.
I hope your problem gets solved to your satisfaction.
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