Originally Posted by Rick76

I found the service information that describes how to check and adjust the secondary stage throttle valve. This is an easy check - all that has to be disassembled is remove the air cleaner. This could very well be the cause of your hesitation but not the rough idle. Autozen had a good point about checking the valve adjustment - you'll find posts on how to do that. Buy yourself a 17 mm crowsfoot and quality metric feeler gauges.
Basically the procedure for checking the throttle valve is to place a weight on the valve near the rear edge (closest to the firewall) and the valve should open 1.5 mm. The weight is 112 plus or minus 2 grams for 73 and 74 Federal, 143 grams 74 California, 170 grams Federal and Cal. for 75,76. I made a crewd test weight out of an old wheel weight, trimming it to the desired value. Mercedes had a test fixture for the test, but I doubt if anyone has one now.

The quote from the SI is:
"Check upper throttle valve for free movement.
Carefully place the correct test weight on the upper throttle valve (do not drop weight).
The throttle valve should be moved downwards slightly (approximately 1.5mm/.06").
If the throttle valve does not open at all or it moves more than 1.5mm, the tension on the return spring must be corrected accordingly with the adjusting screw. Loosen clamping screw prior to turning the adjusting screw. Recheck movement of the throttle valve with test weight. Retighten clamping screw."