The check engine light is on, on the Head-up Display of my car. It revs up and down when the car is not moving. I checked the cylinders as I was told at the dealership that if they misfire, this can happed. I checked that out and the same problem happened. I also had the transmission fluid changed but to no avail. I took it to the shop again and they told me it is the intake manifold causing this. I would like some advice and another opinion about the cause of this issue. Thank you.
Hello. If the engine speed is going up and down as the vehicle is sitting there and running, then it is not a transmission problem. It can be an intake manifold issue as they mentioned, as I have seen a lot of these fail and cause this. Most of the time though, it is caused by a faulty air flow sensor. When this is not reading right, then the computer cannot control the idle. I would scan the computer for codes to see for sure what the computer is seeing. If you are going to have this repaired, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose your Check Engine Light and proceed with appropriate repairs.