Faulty Lambda Sensor(s)? Poor running from cold. Brake Pressure Solenoid Intermittent Warning

[MarkyB]

Trying to figure out what's going on with my 2001 AMK S3 with 71K miles. It's a TBW model.

I am the only owner and other than fitting aero-wipers it's stock; no remaps or performance upgrades fitted.

It's my daily-driver and gets a 15-20 mile round trip to/from work during the week (mixture of city traffic and a brief jaunt on a fast A-road) with a longer journey (motorway driving) every couple of weeks.

A couple of months ago I noticed that the the Emissions Warning Light (the one shaped like an engine) came on orange and stayed on. I've tried the usual fixes (see below) and cleared the warnings, but the light comes back on again after a couple of drives.

The engine fires up first time, but then runs unevenly (misfires?) for the first 30 seconds or so, then runs unevenly; underpowered, feels like it might stall when I apply throttle. It takes a while for the engine to warm up, but then it runs OK. I've taken to setting the climate controls to "ECO" to reduce the load on the engine when it starts and waiting until the engine has warmed up before turning it back to "AIRCON".

I've cleaned the MAF, Air Intake Temperature Sensor, the Throttle Body (which was filthy) and checked the hoses for obvious leaks and wiring (such that I can get to) for obvious breaks. Have also run a bottle of Cata-clean through the engine. The engine does now idle smoother when warm, but still runs poor on a cold start, particularly if the ambient temperature is cool; I didn't notice it much when the weather was warmer, but now the weather has turned cooler, it's struggling more.

Error codes suggest a fault with the O2 (Lambda) sensors (plural?), but I'm not sure where they are or how to go about replacing them. Quick check on eBay suggests that it's not a cheap part to go replacing on a whim.

There is also an intermittent fault code for a Break Pressure Release Solenoid. Have not noticed any issues with breaking, other than the brakes squealing under light breaking; the car still stops OK. The brakes work fine under heavy braking without any noise. Have standard Audi disks and pads fitted.

Thanks,

Mark

Chassis Type: 8L - Audi A3/S3
Scan: 01,02,03,08,15,17,22,35,37,45,54,55,56

-------------------------------------------------------------------------------
Address 01: Engine
  Controller: 8N0 906 018 J
  Component: 1.8L R4/5VT  G  0004
  Coding: 10710
  Shop #: WSC 01236
  WAUZZZ8LZ11003345  AUZ7Z0A1839630
4 Faults Found:
16684 - Random/Multiple Cylinder Misfire Detected
  P0300 -- 35-10 - - - Intermittent
16688 - Cylinder 4 Misfire Detected
  P0304 -- 35-10 - - - Intermittent
16701 - Rough-Road Hardware Not Present
  P0317 -- 35-10 - - - Intermittent
17540 - Oxygen (Lambda) Sensor Heating: B1&B2 S1: Heating Circuit Short to Plus
  P1132 -- 35-00 - -
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 03: ABS Brakes
  Controller: 8N0 907 379 E
  Component: ESP  20  CAN  V005
  Coding: 18448
  Shop #: WSC 01236
1 Fault Found:
00812 - Brake Pressure Release Solenoid (F84)
  35-10 -- - - Intermittent

 

[badger5]

coil packs, plugs, airleaks... a good starting point

 

[MarkyB]

Spark plugs were changed in June during the service which included an oil change, brake fluid change, new air filter & new pollen filter.

I replaced all four coil packs myself about 3 years ago, the previous set had been on the car for ~9 years.

Any thoughts on the lambda sensor fault code? Looks a bit weird to me, could be a fault with the wiring somewhere?

BTW, are there one or two lambda sensors and where are they/it?

Thanks.

 

[MarkyB]

OK. Much reading later and to answer my own questions and for the benefit of anyone else reading this; there are two lambda sensors, pre-cat used to manage fuel trim and post-cat used to monitor emissions and make sure the cat is still working.

I took the throttle body assembly off (again) and cleaned everything up (again), cleaned the air intake temperature sensor (again) and then carefully put everything back together (again). Ran a throttle body alignment using my ye olde VAGCOM (again) - actually twice as I accidentally tapped the accelerator pedal the first time when I was trying to keep my laptop steady.

Car now gets up to temperature faster and feels like there is more power so could have been a leak with me not putting the TB back on snugly enough and/or the TB being out of alignment.

Have a replacement gasket for the TB, but as the original one was still intact and was firmly stuck to the TB decided to leave it for another day when I have some gasket remover and a couple of days when I can do without the car.

I decided that I'd check / clean the Manifold Air Pressure (MAP, not MAF) sensor that sits on top of the passenger-side turbo inter-cooler, but couldn't undo the screw/bolts that hold it in place as they were corroded. I thought I'd managed to loosen one of them, but I think all I've done is snap the screw/bolt as it spins around and doesn't come lose / out Am guessing that I'd have to remove the bumper to get to the IC to remove it be able to drill the screws / bolts out, at which point I hand it over to a garage to do that job.

 

[<tuffty/>]

The MAP sensor uses captive nuts... if they are spinning then that is indeed IC out for drilling... had a similar thing with the MAP tube on my S3... had to replace it in the end as it wouldn't seal properly

<tuffty/>