The sensor by the oil filter and water pump is the Oil Pressure sender unit. Sometimes you may see sensor in the oil pan which would be for oil temp.
If you are having idle problems more likely you have a problem with air/fuel mixture indicating possible vacuum leak or bad AMM, etc. Also may be caused by lack of, or weak spark. If your car is not getting spark to one of the cylinders the car idle would drop to below normal. Another possibility is air box thermostat that opens/closes the flap in the air box bringing hot vs. cold air. Common failure is for the thermostat to die and keep hot air flowing into the airbox from the exhaust side (pre heat hose). This throws off the AMM and you get crazy mixture.