You have an oil pressure gauge? (Not a light?) then you have a Rallye dash cluster. In that case the IVR supplies all three gauges, oil, temp, and fuel.
It is nearly impossible for the IVR to be bad and causing this problem IF the oil gauge works "normally."
This is likely a bad sender, the engine "is" actually running warm, or else the sender wire is damaged and shorting some of the time.
