Poor performace
Most sensors in the engine are block-grounded. If the block is not properly grounded to the chassis, you have poor grounding and everything including the guages and sensors are going to get moderately upset.
I know electrical problems suck, but it sounds like you just need to find the ground strap and inspect it. If the connection is better made after the car warms up, it could be some kind of poor connection, which is harder to find than a non-connection.
\chris



