After installing a Dinan chip in my 1990 525i, I have a couple of problems. First, at a full stop my idle is very rough and occasionally the car stalls. Pushing the gas just enough to get the rpms over 500 results in a smooth idle. Second, I hear a high pitched sound coming from the engine. Almost like an old computer monitor. It might not be a result of the chip, but I just started noticing it. Please help!