Lumpy on idle

[Redsfan2008]

Hi everyone, my A4 (B9) tdi ultra seems to be a bit lumpy at idle. Runs like a dream whilst driving but at idle it rumbles like a tractor and the gear lever shakes. Any ideas?

[jdragon]

How many miles has it done?

What's your driving pattern?

Assuming from driving like a dream it's responsive.

There could be a lot of causes; blocked fuel filter, dirty MAF sensor (was cause of my old B8 lumpy idle), engine mount. some will produce other symptoms e.g. bad injector and black smoke.

More info would help.

[Redsfan2008]

Thanks for your reply jdragon. The car has done 128000 miles so quite a lot, but full service history. My driving is motorway/urban mix. But to reiterate, the car drives perfectly, and responds to throttle inputs very well. 

[jdragon]

Run a bottle of cataclean through it. Quickest and cheapest option right now.

And be sure to drive it until you're display is showing 50 miles left, so it takes more through the system than the recommended 15 minutes on the bottle.

Report back the outcome.

[Redsfan2008]

4 minutes ago, jdragon said:

Run a bottle of cataclean through it. Quickest and cheapest option right now.

And be sure to drive it until you're display is showing 50 miles left, so it takes more through the system than the recommended 15 minutes on the bottle.

Report back the outcome.

Will do thanks. I’ll let you know if it makes any difference.  
 

[jdragon]

Might be worth checking the glow plug caps are well seated too.

Sometimes problems can be resolved by the most simplest interventions.

 

To give an example: abs light came on my in-laws dash. Garage quoted them £400/1000 to fit a used/new part respectively.

After a little Google and 5 minutes looking at the car, I discovered it was a blown fuse.

 

[Redsfan2008]

8 minutes ago, jdragon said:

Might be worth checking the glow plug caps are well seated too.

Sometimes problems can be resolved by the most simplest interventions.

 

To give an example: abs light came on my in-laws dash. Garage quoted them £400/1000 to fit a used/new part respectively.

After a little Google and 5 minutes looking at the car, I discovered it was a blown fuse.

 

I guess there are so many things that can happen to a modern car aren’t there. First thing I’ll do is put some Cataclean in and see if that helps. Cheers. 

[Stevey Y]

38 minutes ago, Redsfan2008 said:

I guess there are so many things that can happen to a modern car aren’t there. First thing I’ll do is put some Cataclean in and see if that helps. Cheers. 

Hi get the car scanned for codes, it sort of helps with the guesswork situation if no codes then you have an uphill task.

Steve.

[Redsfan2008]

11 hours ago, Stevey Y said:

Hi get the car scanned for codes, it sort of helps with the guesswork situation if no codes then you have an uphill task.

Steve.

Cheers Steve, I’ve got an OBD2 plug so I’ll have a scan to see if anything comes up. Thanks again. 

[Redsfan2008]

On 9/8/2022 at 6:53 PM, jdragon said:

Run a bottle of cataclean through it. Quickest and cheapest option right now.

And be sure to drive it until you're display is showing 50 miles left, so it takes more through the system than the recommended 15 minutes on the bottle.

Report back the outcome.

Hi, sorry it’s been so long letting you know. I had too much fuel in the car and had to use it before putting the cataclean in.  I have now used the cataclean and the difference is quite remarkable. Much smoother at idle and mpg is better too. Good advice thanks. I intend to use a bottle about every 3 months. Cheers. 

[jdragon]

5 hours ago, Redsfan2008 said:

Hi, sorry it’s been so long letting you know. I had too much fuel in the car and had to use it before putting the cataclean in.  I have now used the cataclean and the difference is quite remarkable. Much smoother at idle and mpg is better too. Good advice thanks. I intend to use a bottle about every 3 months. Cheers. 

Glad you have seen an improvement. I passed that little gem forward from @Stevey Y

The next thing I was going to suggest was giving the MAF sensor a clean with the stuff from Liquid Moly. This too made a huge difference to my previous car, when I had nothing to go on from the scan.

I'd also recommend using Archoil fuel additive.