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When cam deviations change over long periods of time, the most likely - although not only cause - can be wearing variocam chain pads. Replacement parts are inexpensive. The major cost is the labor time to remove the valve covers.
If your pads are wearing, the deviations will only get worse. If your numbers are accurate, you should determine the root cause given your on the edge of being out of spec. IMS in only one of many failure modes in 986 engines.
Sometimes you can identify wearing pads by finding brown chunks in the oil sump.
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