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Ali's Dad
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229 Posts
Discussion Starter · #1 ·
I have searched both on this forum and others to help resolve what I believe is an issue. My 03 1.8T NBC has developed a case of resonation. I have most likely just made up the word but it describes the situation.

Two weeks ago I replaced all spark plugs (No idea how old they were as we have had the car 2 years and only put 8K on it - now at 114K).

Since replacing the plugs the gas mileage has dropped from 28mpg to 22 mpg. The car also now vibrates under all conditions. Not axles, not transmission, not tires/wheels.

TB appears to be good, pulled all of the plugs and checked for issues - none.

Ran VAG-COM - only 1 error for a drivers door switch.

Vibration is real and it almost feels as if the exhaust is loose and vibrating - except it is quiet.

No loss in power - actually seems to have improved.

Checked all vacuum lines, all air hoses.

I have ordered new coil packs - just in case (although no codes were found).

Anyone have a similar experience?
 

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Peace Love & T.o.D.
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2,802 Posts
May sound like a dumb question, but did you gap the new plugs? Or did you at least check the gap before the install?
 

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Ali's Dad
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229 Posts
Discussion Starter · #3 ·
Did not gap them or check them. NGKs are supposed to be pre set to the bug's specs (they actually say not to gap them on the box as it might damage the platinum). But I will check them when I replace the coil packs.
 

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Registered
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3,690 Posts
Mileage drop is most likely due to the engine running too cold. This is a COMMON problem with these engine.

Thermostat will go soft, engine temp will drop, there will be no indications.

You need an OBDII tool that supports Live/Realtime Data.

These engines should run around 205F/96C even when cruising on the highway.

I have seen these engines run as low as 170F all day long without a single warning or code, this is how all of these engines ended up with clogged oil pickups.

Been there, done that.

The resonation issue, could be either the alternator pulley is seized, on these engines it is a complicated on way clutch pulley, somewhat rare and unusual or you need to check the exhaust system out.

Get the car up in the air and start "bumping" the exhaust with your palm or a rubber mallet and listen for noise. I had a gum ball size chunk inside the 2 catalytic converters dancing around making noise. It was a piece of the front catalyst that broke off.

I replaced the convert many years ago, but recently I have something in the rear of the exhaust rattling, not sure if a baffle has broken spot welds inside the resonator/muffler, if there is a heat shield rattling or of there is a piece of catalyst that broke free again and is in the exhaust system?
 

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Ali's Dad
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229 Posts
Discussion Starter · #5 ·
Thanks for the replies. I am fairly certain the resonation is not exhaust related - as I didn't quite describe the issue correctly. Since changing the plugs the car vibrates - vibrates at such a high frequency that it causes the plastic insides to also vibrate which is best described as resonating. I did swap out all the coil packs today- i will give it a bit of test drive later to see if there is an improvement.

I put a new alternator on back in July - pully could be bad but I dont' think so - seems to be turning.

Thermostat is another issue entirely. I will check it out. I have access to a VAG-COM setup so next week I will borrow it and drive around with it in real time (I have an 80 mile round trip commute so I should get some good data).

May sound silly but I have to say on this Thanksgiving that besides being thankful for family and health I am especially thankful for the .org. Y'all have given me the ability to keep my daughter's bug running when any sane person would have sold it. Thanks.:)
 

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Ali's Dad
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229 Posts
Discussion Starter · #6 ·
Test drive indicates that the coil packs fixed the problem. Vibration is about normal. Now on to fixing the suspension.:)
 

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Peace Love & T.o.D.
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2,802 Posts
Did not gap them or check them. NGKs are supposed to be pre set to the bug's specs (they actually say not to gap them on the box as it might damage the platinum). But I will check them when I replace the coil packs.
Yes, but SUPPOSED is a big word.
They are very rarely gapped correctly.
Out of the four plugs, I would bet that two were off tolerance.
 
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