Rough idle and slow to acclerate?

Tiny
GLI_GUY
  • MEMBER
  • 2016 VOLKSWAGEN JETTA GLI
  • 2.0L
  • 4 CYL
  • TURBO
  • 2WD
  • AUTOMATIC
  • 90,000 MILES
My car is idling rough and feels slow at acceleration, spark plugs, and coil packs are brand new. I was thinking of cleaning the throttle body really good, and running some seafoam and isoheet through the system, if that doesn'tt fix it I am at a dead end. Also, my cruise control stopped working.
Friday, September 2nd, 2022 AT 11:06 AM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

Is the check engine light staying on when the engine is running? If it is, the first thing I recommend is having the can-bus scanned for diagnostic trouble codes. CAN stands for controller area network. Basically, the different computers/modules in the vehicle are tied together via a few wires. This type of scan will retrieve codes regardless of the module storing them.

Here is a link that shows how it's done:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

Also, let me know the following.

Did this happen all at once? Is there any smoke from the exhaust? Do you notice any odd sounds or odors when the vehicle is running? Does anything rattle under the vehicle? For example, is there a rattle or odd sound coming from the exhaust system?

Let me know.

Joe
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Friday, September 2nd, 2022 AT 9:17 PM
Tiny
GLI_GUY
  • MEMBER
  • 4 POSTS
No not all at one time, rough idle was first, then acceleration and poor fuel economy started getting shotty. Then cruise control started not working on and off, the. Airbag light came on, then check engine light. No smoke from the exhaust. I have it down in my opinions to either the PCV valve (it has crazy amount of vacuum in crankcase when I pull oil fill cap while idling.) Or throttle body is dirty or faulty, I just wanted an expert's opinion.
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Friday, September 2nd, 2022 AT 9:24 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

I don't see how the PCV could do it. You want that vacuum to remove crankcase gasses and pressure.

As far as the throttle body, it could cause the rough idle, but a loss of power after idle is odd. If you plan to clean it, here is a link that you may find helpful:

https://www.2carpros.com/articles/throttle-actuator-service

Also, take a look through this link. It could be a partially plugged catalytic converter.

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

Let me know what you find.

Take care,

Joe
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Saturday, September 3rd, 2022 AT 10:15 PM

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