It sounds as if you are only able to check low side pressure. You REALLY need to monitor both.

One other thing. On the Chevy trucks I've messed with, it is not uncommon for them not to get enough airflow at idle. The fan clutches wear out or something. You can easily tell that this is going on with manifold gauges, because you see the high side pressure go so high you feel like you need to hide behind something.

Until you can monitor both sides, you are handicapped in trying to determine the problem.

Hope this helps.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

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