RPMs Jump and Fall after being parked overnight?

KMB687

MEMBER
2015 VOLKSWAGEN JETTA
1.8L
4 CYL
TURBO
2WD
AUTOMATIC
91,000 MILES

Upon start after sitting for an extended period (overnight) and after starting and driving just a bit, the engine's RPM's begin to jump and fall, or hang. There is a rough idle that accompanies this behavior beyond just the RPMs jumping. It does shake the entire vehicle. I have noticed it will only do this before the engine is up to temperature, but again, only after it has sat for an extended period. This issue used to only happen maybe once every other month, to once a month now nearly daily.

This has been developing over the last year or so. I have changed the spark plugs, fuel filter, air filter, and had a computer recall update done. I have just put in a "Gum Out" additive as well, which has not changed the behavior.

Attached is a video my wife took.

Video (Click to make bigger)

1 Reply

KEN L

MASTER CERTIFIED MECHANIC
43,047 POSTS

Thanks for the video, did this occur after the spark plug change? If so, I would remove the spark plugs and check for cranks in the plug which is common when you change them out also only use the ones mentioned below. It is very important to only use the spark plugs VW recommends. If okay, I would check for vacuum leak when the engine is cold.

This guide can help us fix it:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

We should run the codes as well.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

It could be the MAP sensor is starting to go out

Manifold absolute pressure sensor 06L906051B $96.67

Check out the images (below). Please let us know what happens.

Images (Click to make bigger)