I have a 1999 VW Jetta (80K miles). The check engine light goes on hen there is moisture in the air (something that has happened since I bought it). The resting rate for the RPM is about 8. Over the past few months I’ve notice that at stop lights the RPMs suddenly drop to about 7 for half a second then returns. It also goes up to about 40 RPMs before it “shifts” gears after I reach about 30 MPH. What could be wrong? I admit, I don’t drive the car much … maybe 50 miles a month.
Please take the car to autozone and post the code here. It is always a start up point to find the problem.
Getting the codes is the first step and odds are that it’s related to the ignition system; and especially so if the car has never seen a set of spark plugs in that 80k miles.
Bad spark plugs contribute to failed plug wires which contribute to failed coils and moisture in the air will exacerbate this problem quite a bit.
Try a new set of spark plugs and spray the coils/wires down with some WD-40. Maybe you’ll get lucky and not need the more expensive stuff; knock on wood.
Do not spray the wires with wd40. Never. That is only going to attract more moisture until they fail completely. The dust that will settle on the oil will speed the failure. Spark wire should be clean and dry of all contamination. Clean wires means not problems. Check for sparks when the engine is running in the dark. Any glow from the wires should be traced down.
You could try my brother’s suggestion when we were kids “Just grab the spark plug wires, one at a time, while it is running. If one is cracked you’ll feel it.”
You can tell if you need new wires when your hair stands straight out, you jump back quickly from the engine and smack your head on the hood, then you fall on your behind on the ground and twitch for a while.