If you don't get the codes, you'll just be throwing parts at the problem...and parts are not cheap!

But if you want to go ahead and do it anyway, I would suggest looking at the cheapest solutions...spark plugs, spark plug wires (possible issue with no rev/throttle), and replace old vacuum hoses (typical culprit of the idle surges).

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car