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I'm guessing this is fuel injected, correct? I would consider the fact that your fuel pump may actually have been bad, but besides that, you may want to look at:
Idle Controller (if you have one--I'm not familiar with this year)
Possible fuel leak somewhere (gaskets, lines, etc etc)
Check fuel pressure while running and see if it correlates with your rpm jumps.
I have checked the fuel pressure, the original problem was stalling at take off, replaced the filter, pump, screen, hoses and the overload relay. Cars runs smooth down the road but the idle goes up and down, I am wondering about the idle control sensor? Such a pain it has no computer connection, cant read codes...
I believe idle control valve on these was screwed into side of the block under the intake manufold, sensing coolant temperature and opening/closing air supply. It would not make the RPM fluctuate because it is working in very slow motion and it is closed when engine is warmed up. Check all the clamps on fuel hoses to pump and tank, you may be sucking air into fuel while pumping it out of tank. You can check your new pump by taking off supply hose from fuel distributor, volume should be one quart of fuel minimum per 30 seconds. There is also screen in the fuel distributor inlet where the supply hose fitting is screwed into and also in warm up regulator under supply hose fitting. Follow the fuel line from pump to engine and you will find them.
1999 ML320 230K miles
2003 Lexus GX470 285K miles
2001 ML320 162K miles
1980 280SE EURO W126 156K miles 142mph top speed SOLD
1984 300D TURBO DIESEL W123 SOLD