Will a clogged "Cat" cause poor idle

[SledDawg2]

I have been trying to assist a friend with his TDI.
its a 2003 Jetta wgn manual transmission.

His engine idles with a vibration and at low speed.
This vibration can be felt through-out the car.

The car accelerates good and the vibration diminishes as you gain speed.

My question is:
Can a clogged cat cause this type of idle / vibration ?

 

[IndigoBlueWagon]

Doubtful. More likely a fueling problem. Look at VCDS for injection quantity, whether or not the timing graph "floats," and any fault codes. And look at injector balance.

If you don't have VCDS run a can of Diesel Purge through the car and see if it idles better. Run it on the Purge straight, don't add it to the fuel tank.

 

[Rembrant]

I have been trying to assist a friend with his TDI.
its a 2003 Jetta wgn manual transmission.

His engine idles with a vibration and at low speed.
This vibration can be felt through-out the car.

The car accelerates good and the vibration diminishes as you gain speed.

Did he buy the car like this or has he had it a while and this is a new problem that just started all of a sudden?

 

[turbovan+tdi]

Could be motor mounts, DMF, miss due to injector or compression issues.

 

[Herm TDI]

OK...Some more info:
I've had this car here at my place to get a look-see.
The first thing I did was to get the car onto a lift to further isolate the source/ cause of the noise.

The noise is coming from the engine. This noise is a constant low pitch drone (almost like the engine is groaning). This groan type noise will dissipate above 1,100 R.P.M.

I removed the serpentine belt to further isolate the source such the accessory pack components (A/C, Alt, P/S).

With the transmission in neutral, serpentine belt removed and a new harmonic balancer the noise is still there.

The engine & transmission mounts and the dog-bone have been replaced.

Does anyone have any ideas ?

 

[Rembrant]

The engine & transmission mounts and the dog-bone have been replaced.

Are they stock replacement mounts & dogbone?

 

[Paul S]

Intake air leak before turbo entrance???

 

[Herm TDI]

Update:
Looking around via VCDS and I found the idle speed was low (aprox 845 RPM)
I took the adjustment to the max value (32803). This adjustment resulted in idle speed of 945.
This adjustment DID reduce the vibration / drone noise!

I would like to get the idle up near 975 RPM.

My question is: is there a any mechanical adjustment like the "hammer mod" to change the idle speed ?

 

[Herm TDI]

no leaks

Intake air leak before turbo entrance???

The air inlet system is solid. This was one of the things that "dawg" looked into.

 

[Herm TDI]

mounts

Are they stock replacement mounts & dogbone?

The owner bought the mounts from a local VW dealership (has the receipt).

 

[Rembrant]

The owner bought the mounts from a local VW dealership (has the receipt).

Ok, cool. I was just thinking out loud...maybe somebody had installed a poly dogbone or other mounts...that would cause vibe at idle, and droning noise in cabin perhaps...that would smooth out at higher RPM's.

 

[UhOh]

This is interesting in that I often have wondered how idle could fall below factory setting and given that the ECU should be able to adjust for it.

Seems that cranking the idle up via VCDS is bandaid-ish, that the source of the issue is still there somewhere?

Could the crank speed sensor have anything to do with this?

 

[nayr]

Def not a clogged cat, it will act more as a rev limiter than anything else..

Ive had it happen, after buying a used poorly running car with a bunch of CEL codes that I fixed up.. It does anything but get better as the RPM's increase.

How many miles are on the car? They get loose with age, have you compared the idle vibration and noise with another diesel of the same generation? If its a new owner perhaps they are just paranoid about normal diesel idle.

 

[UhOh]

It would help if someone could probe around with a stethoscope.

Herm, did you check out performance via VCDS? Seems like there ought to be a hint via IQ deviation. Higher revs tend to smooth things out (which may disqualify it being a crank speed sensor).

 

[AndyBees]

Could be a slightly burned exhaust or intake valve.

So, since we are all shooting with a shot-gun, I suggest doing a compression check. And, definitely check injection balance with VCDS.

 

[GreenLantern_TDI]

Id straight pipe it.

 

[UhOh]

Id straight pipe it.

How is this going to do anything with the problem?