1989 Volvo

I have a 1989 Volvo wagon that won’t go above 2000 rpms. Any ideas. I have checked numerous things and replaced fuel relay, spark plugs, air mass meter, air idle motor and fuel pressure gauge. Both fuel pumps work great.

Will the engine rpm go above 2000 when the gear shift is in PARK or NEUTRAL? If so, the problem is, probably, not the ignition (spark).
Replace the fuel filter, and check the fuel pressure with the rpm at 2000, and the gear shift in DRIVE. This places the engine under load, simulating driving.

The car will not go above 2000rpm in park or neutral. It surges between 1000 and 2000 rpms. I have already checked the fuel filter.