Here is how our '91 190E 2.3 behaves, since I fixed the idle. Note that the idle circuit of yours is a different design (I believe). When the engine is first started cold, idle goes to about 1200 rpm - not racing, idling smoothly - then drops to 750 rpm in 5 - 20 sec. Idle may go a bit higher, maybe 850, for awhile if it is pretty cold out.
If you have an idle control valve, it may be gummy and need cleaning. Injector cleaner in the fuel tank will NOT do this, it must be removed. If the connecting hoses are hardened with age, they should all be replaced, and I found the OVP relay apparently had bad contacts. Also check for proper operation of thermostatic elements and check for vacuum hoses loose.