[mlambrecht82]

The sensors do work when the engine is cold, you have HO2S (heated oxygen sensors) so they heat up to over 600 degrees almost instantly, but the engine is in open loop, in other words it disregards the signal from the o2 sensors, until the engine coolant temp. has reached a certain level. When the engine is cold it dumps extra fuel in to help the car warm up faster. Once the engine is warm it monitors the o2 sensors to keep the car at stoichiometric. Check for Trouble codes using your instrument cluster and if nothing shows up then just wait for the car to warm up before you rev it. Especially if its been sitting for a while and all the oil has leaked down in to the pan, metal on metal is a bad thing, let the oil get inbetween them first.