Q: Car Revving in Idle. Performance not affected.

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Hello,

Over the past few weeks my car has been revving in idle. It also tends to run just below optimum engine temperature. Engine management light was on. Temperature gauge tends to be just left of mid-line. I brought it to VW dealership to have it assessed. They diagnosed the problem as being the Throttle Body. Cost 735 for part and labor. Price in Euros as I'm writing from Ireland. However, when I got the car back it was the exact same way!! Except the engine management light was off. They took it back and then said it was "Breaker Valve on Rocker Cover". They replaced this. 190 Euro. I spoke to the mechanic and asked is he sure that the Throttle Body had a problem in the first place. He explained that a faulty Throttle Body can affect this Breaker Valve on Rocker Body. Does this sound ok? I just feel that the throttle body was not the primary problem. I have the old one so I could get it checked out. Car still driving great.

Thanks for taking the time to read this. Cormac Cawley

My car has 180000 miles.
My car has a manual transmission.

If I understand you correctly, Your car is working properly now, but you wonder if you really needed to have the throttle body replaced. The short answer is, it’s impossible for me to say. But here is what I think might have gone down. The throttle body on your car is a very common failure. For some reason VW just can’t seem to make a throttle body with any staying power. It’s usually the first really expensive parts replacement that VW owners have to do on their cars. But it has redundant circuitry in it, so if one of its position sensors fails, another can take over and the only thing you notice when it first fails is that the check engine light comes on. Fast idle is a classic symptom of a failing throttle body as well. So when the technician scanned your car, and found codes for a bad throttle body he assumed that switching the throttle body would solve your idle problem and didn’t look for any other failures. Most of the time he would have been right. So I expect your throttle body DID need to be replaced, and if you were to put it back on the car you would probably get a check engine light on for your trouble. But any source of air getting into the engine that doesn’t go around the throttle body will give you a high idle, so if the break valve was leaking or sticking, that alone could have been the cause of the high idle.

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