Just a thought. Might check around for a vacuum leak. A hose that has cracked, or come loose, or something like that. That can effect the idle speed on any gas engine.
Best of luck!

__________________
past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)