1.8T Hunting on idle

[scotta]

Bit of help guys please.

Ye wife's Got an A4 Avant 1.8T which has started hunting a bit on idle and running a bit rough just on idle. I took it for a drive and it pulls fine right through the rev range. From the bottom of second gear on WOT right round to about 6000 it's smooth, pulls well and you can hear the turbo spool ok.

However On overrun it seems to want to run on a bit. Additionally when the car is stationary revving it to 4000 rpm then releasing the throttle the rev's fall gradually for a couple of seconds before falling as they should back to idle. Idle then hunts between about 700 rpm to 1200 rpm and the engine is a bit rough....

Initially I thought Coil pack but they were all done about a year ago under warrenty and its not running on3 cylinders as it has done in the past when the coil packs went.

I'm gonna get it on vcds later tonight to check for any fault codes.

Any ideas?

[james]

check your ignition amp, it is on the airbox.

[scotta]

VCDS-Lite Version: Release 1.0
Monday, 05 November 2012, 20:37:44.
Control Module Part Number: 8E0 909 518 AL
  Component and/or Version: 1.8L R4/5VT         0003
           Software Coding: 0011501
            Work Shop Code: WSC 63251
4 Faults Found:
17705 - Pressure Drop between Turbo and Throttle Valve (check D.V.!)
        P1297 - 001 - Upper Limit Exceeded
16684 - Shareware Version. To Decode all DTCs
        P0300 - 008 - Please Register/Activate
16685 - Shareware Version. To Decode all DTCs
        P0301 - 008 - Please Register/Activate
16686 - Cylinder 2: Misfire Detected
        P0302 - 008 - Implausible Signal

[GLIDN]

can be one of the following, had tis on the girlfriends GTI 1.8t.

Firstly, pull the throttle body off and clean it internally. Also clean contacts on throttle sensor. Replace coolant temp sensor (I know it sounds weird, but is aiding to issues)

As you have misfiring, it could be plugs and or coil-packs. With those Audis A4's the coil packs are not that expensive, Perhaps it would be a good time to replace all 4 and new plugs? Just do not replace one only, as it will start a chain reaction and each one of the others will blow. (to do with resistance differences)

There after you should be sorted. It could be ignition Amplifier as pointed else where. Swap coil packs around and see if misfire stays on cylinder 2 or goes to allocated cylinder. If it changes location, it's coil pack. If it's stays on cylinder 2 it's ignition amplifier.

Hopefully this helps.

[james]

from that vcds,  sounds like you  have a boost leak.  check the pipe under tha manifold and the one that runs down the back of the engine.

[GLIDN]

Something else I forgot to add, replace all your vacuum hoses with 4mm silicone hose.
Lastly replace your diverter valve with a Audi S3 710N valve. Don't let the stealerships offer you an A4 replacement as they are almost twice the price if not more these days.

You won't be replacing the 710N valve for a few years. Ours has done 65000 miles at 20psi boost now. 710N still holding strong.

[scotta]

Update -

ive rescanned it on VCDS and got some more codes

17705 - Pressure Drop between Turbo and Throttle Valve (check D.V.!)
P1297 - 001 - Upper Limit Exceeded
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 008 - Please Register/Activate - Intermittent
16685 - Cylinder 1 Misfire Detected
P0301 - 008 - Please Register/Activate - Intermittent
16686 - Cylinder 2: Misfire Detected
P0302 - 008 - Implausible Signal - Intermittent
16891 - Idle Control System RPM: Higher than Expected.
P0507 - 001 - Please Register/Activate - Intermittent
17544 - Fuel Trim: Bank 1 (Add): System too Lean
P1136 - 001 - Please Register/Activate
16688 - Cylinder 4: Misfire Detected
P0304 - 008 - Implausible Signal - Intermittent

Looking on the Ross Tech Wiki common theme seems to be a vacuum leak. This is where it gets tricky

So far i have

Removed and Cleaned the Throttle Body.
Visually Checked the hoses i can see from the top for splits or tears. Checked hose connections. Sprayed a bit WD40 about to see ifi could get a raise in engine revs. Found nothing
Replaced the Coil Pack in Cylinder 2 - Had a spare!

Plugs were replaced a month or so ago when i serviced it. It runs fine other thatn on idle and its not down on power so i think they are fine
Ignition Amplifier - Dont think the A4 has got one of these. Ive googled and i can only find a locaion for it on the A3
Cant get the PCV valve off as it seems to be on with some funky clips. I would have thought if there was a problem with that the fault would go away when you took the oil filler cap off? Not 100% sure about that tho so welcome to be told different!

Running out of ideas now. Only thing ive got left is to change the DV as ive got a spare one in the hut that would fit it.

Failing that any ideas?

P.S. Can you do a throttle body alignment with the shareware version of VCDS?