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Clean Valves And Lifters?

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I just bought a 91 LS 400 with 213,000 mi. I just replaced the Starter, & PCV Valve. The engine makes a tapping noise when under acceleration. When I replaced the PCV Valve, I noticed that it seemed pretty sluggy in there. Would it help to remove the valve covers and clean the valves and lifters? If so what should I use? I know that in 97 the dealership ran some GM Top Engine Cleaner through it to remove a tapping sound. I wonder if I should try that again? Has anyone used this stuff on thiers? The three causes of this seem to be:

1. Sticky valves

2. Valve adjustment

3. Exhaust leak

4. Timing advanced

Do you have to reset the timing when you replace the timing belts?

I have a lot to do to this thing. Any input is appreciated.



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WHy waste all that time ,just buy a bottle of engine flush and run it then replace the oil (and filter) with cheap stuff for a week then replace with synthetic to make sure all the flush is gone.

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They work amazing i have used tehm on my wifes sunfire my civic ,lexus and the list goes on.

I use the penzoil one they all are pretty much the same

The lifters getting unstuck makes the biggest power and noise difference.

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