Your system is running properly.

At idle, the compressor will cycle a lot. At about 2,000 rpm, it will operate most efficiently. This is also the speed where the temperature will be the lowest and where the AC system should be checked.
Adding too much R134a will decrease the amount of expansion allowed and cause the system to run too warm.

Most 1998+ models do not have evaporator leak problems, like the 850s. They do develop leaks in the receiver/dryer tank if there is a lot of salt during winter driving conditions - very prevelant here in the USA. This does not seem to be your problem.

As for the drag on the idle when the compressor engages, check/clean the idle control module as it is not reacting fast enough to the speed change. This is common at low rpm while driving.

Klaus
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I still miss my 164