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Can you feel the vibration, or do you just hear it ?
Can you narrow the search with a mechanics stethoscope ?


If you feel it:
Probably an air leak,
check all vac lines and attachments
Check intake, everything from filter to valves.
or
Uneven compression,
check compression soon after running engine.


If you only hear it:
Check for something (such as a heat shield) loose or too close to something else.


Do you have aftermarket drive shafts ?
 

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Discussion Starter #44
I checked for vacuum leaks. Sprayed brake fluid on possible areas. Nothing.

But I am hearing some sort of hissing sound around this hose. (Pic)

will a bad vac. Line cause engine vibration?

-turbo is building factory level boost (10psi)
-there is no engine code.
-Fuel trims are normal.
-Readiness tests come all green per VCDS.
-Axles are original (Raxles)




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I again suggest you check each cylinder compression.
A small air leak can cause mis-firing/vibration. I guess you meant brake cleaning fluid
 

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Discussion Starter #46
I again suggest you check each cylinder compression.
A small air leak can cause mis-firing/vibration. I guess you meant brake cleaning fluid
Yes brake cleaning fluid. I will do a compression test.


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Discussion Starter #47
I checked for the vacuum leaks. There is none.

I hope the following pictures help identify the issue.

At idle, on park, the vibration is almost non existent. (20inhg)

The vibration is horrible at stop, with the ac on, gear on D. Car STOPPED. (10inhg)

Why does the vacuum/ boost gauge move that much when the ac on and in gear?

The car didn’t do it when bought it. I am not sure when it started but it was gradual.






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The A/C on and being in gear put a load on the engine. In order to keep the RPMs the same, the ECU needs to open the throttle more to compensate for the increased load. That effectively reduces the vacuum created by pistons. You can watch the gauge move about 5inhg when parked and the a/c running when the compressor engages and disengages. Same when parked and the SAIP cycles.
 
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Discussion Starter #49
The A/C on and being in gear put a load on the engine. In order to keep the RPMs the same, the ECU needs to open the throttle more to compensate for the increased load. That effectively reduces the vacuum created by pistons. You can watch the gauge move about 5inhg when parked and the a/c running when the compressor engages and disengages. Same when parked and the SAIP cycles.
I occasionally get P0507-001 code. I think I m going to replace the TB.
What do you think?


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I wouldn't consider replacing the throttle body without checking a few things first.
Have you done a TBA ?

I suggest you check each cylinder compression. Have you done this yet ?
Spraying brake cleaning fluid on the vac lines won't detect an internal leak such as a faulty PCV valve or suction jet pump.
 

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Discussion Starter #51
I wouldn't consider replacing the throttle body without checking a few things first.
Have you done a TBA ?

I suggest you check each cylinder compression. Have you done this yet ?
Spraying brake cleaning fluid on the vac lines won't detect an internal leak such as a faulty PCV valve or suction jet pump.
Well, i prepared the engine for compression test.

I removed the spark plugs, removed the fuel pump fuse, turned the key, the engine won’t turn over.

just one click coming from the headlight switch.

With headlights on, turn the key, lights go off and come back when I turn the key off.

Never happened before. What could it be?


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Discussion Starter #52
Update:

Turns out one of the wires from the TCM I soldered (brown-white) came loose.

What’s interesting is vag-com showed no fault code.


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"With headlights on, turn the key, lights go off and come back when I turn the key off."
That is normal.

The compression is fine on all cylinders.

Have you fixed the no crank problem ?
 

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Discussion Starter #55
"With headlights on, turn the key, lights go off and come back when I turn the key off."
That is normal.

The compression is fine on all cylinders.

Have you fixed the no crank problem ?
Thanks.

Yes. It was a loose wire on the transmission control module harness.
The engine starts now.

Now that the compression is good, What is next on the vibration issue?


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I suggest you check all of the breather system, and all of the vac system.
Including the PCV valve, the suction jet pump, and the brake booster.
 
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