Hello,

I've just started having a problem where when I start my car - much more noticeably when cold, it will rev to almost 2500 rpm, come back down and then be really lumpy to the point of almost stalling. The car seems to drive ok but when idling at traffic lights it'll be lumpy again. I'm not that knowledgeable about engines but is there anything simple I could check?

Thanks!

is it only when cold?

To be honest I couldn't say for definite, I haven't done a lot more than the commute since it started so it's pretty cold each time, but when it was warmer it was certainly less obvious.

could be coolant temperature sensor

a dodgy coil pack

maf sensor

need to get it scanned really, do you have vcds?

I have to admit that the engine management light is on, it has been for several months. The code I read said something about the mix being too lean - can't remember exactly, was told not to worry about it too much though by the mechanic who last serviced it... I was given a cheap cable to read the codes and if I remember correctly it was an absolute pain to get it working! (driver issues mainly) but I'll try again to see if anything else has come up since.

may be lambda sensor then. Proper read from a member may reveal more

If the car is fine when up to normal temp then coolant temp sensor failing is the most common cause of poor idle when cold.

If you can post the code that would be helpful.

If it says its running too lean it could be a vac leak at idle.

Hi, this is the output I get:

VCDS-Lite Version: Release 1.1

Tuesday, 16 October 2012, 18:47:57.

Chassis Type: 1U - Skoda Octavia I

Scan: 01,02,03,08,15,16,17,19,22,29,35,36,37,39,46,56,76

-------------------------------------------------------------------------------

Address 01: Engine Labels: 06A-906-032-AUM.LBL

Controller: 06A 906 032 HL

Component: 1.8L R4/5VT G 0001

Coding: 11530

Shop #: WSC 31480

VCID: 6F9150BF3E93

TMBFL21U738675350 SKZ7Z0B1497195

2 Faults Found:

17544 - Fuel Trim: Bank 1 (Add): System too Lean

P1136 - 35-00 - -

17705 - Shareware Version. To Decode all DTCs

P1297 - 35-10 - Please Register/Activate - Intermittent

Readiness: 0010 1001

-------------------------------------------------------------------------------

Address 02: Auto Trans Labels: 01M-927-733.LBL

Controller: 01M 927 733 LL

Component: AG4 Getriebe 01M 4956

Coding: 00000

Shop #: WSC 00000

VCID: 857D92178C2F

No fault code found.

-------------------------------------------------------------------------------

Address 03: ABS Brakes Labels: 1C0-907-37x-ASR.LBL

Controller: 1C0 907 379 K

Component: ASR FRONT MK60 0103

Coding: 0021505

Shop #: WSC 31480

VCID: 321799CBED21

No fault code found.

Many thanks for your help!

Yep I'd say split vac hose somewhere. You have an additive fuel trim error which means its sucking in unmetered air at idle when it shouldn't be and making the mixture lean, you also have the 17705 code (aka "pressure drop between turbo and throttle body") which is usually a split vac hose or faulty valve in the vac system. Check all the vac hoses around and under the manifold for splits. Your boost is probably a bit down as well but not sure how noticeable that would be in driving

The dreaded 17705 code

As chicken says look for split vaccum & boost pipes. There are a couple of braided vac pipes by the inlet manifold that are notorious for splitting under the braid. S pipe under right under the manifold is also a prime suspect too. Check the small pipe going into the top of the DV too, & so on.

Thanks for that guys, not totally sure where all this bits are that you mention but I'll try and get someone to look with me tomorrow! I've definitely seen some braided pipes so I'll start there. Just tried a couple of warm starts by the way and don't get the huge revs after the key turn but it still has a fairly lumpy idle.

Hi again, I went on holiday before I could look at this again but back on it now. Can hear quite a loud hiss when the engine is running, would you expect that? seems to be coming from the driver's side at the front of the engine. Can't find any obvious damaged hoses though. My MPG is shocking, got 19 on my way to work today - a 4 mile trip with 80% of it at 50mph...

Ok, I've found the location of the hiss, it's hard to show where but I'll try in the photos:

That's one end of the pipe, it goes into the T at the location ringed.

This is the location of where the pipe goes, it feels like it splits in two at this point. It's at this end where the hissing sound is coming from, if I wiggle or push this pipe I can change the intensity of the hiss!

Does anyone know what part number this is and how on earth I would get to it to change it?!

Many thanks!

That pipe is commonly referred to as the S pipe, which is notorious for splitting. It runs from the PCV T pipe to the underside of the inlet manifold.

thanks, is that one of these? http://www.ebay.co.uk/itm/VW-GOLF-MK4-BORA-LEON-1-8T-AGU-AUDI-S3-BAM-ARY-AMK-INLET-PCV-BREATHER-PIPE-/160864700273?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2574488771

It feels like the end under the manifold splits into 2 but that could be just that the pipe is just wrecked!

Is it hard to get to to replace?

Thats the one. You can get that pipe from the dealer or TPS too. Not difficult to replace. Best to remove the black mounting plate that bolts to the manifold to get easier access. The PITA bit is breaking the OEM crimp clips that secure the pipe. You'll need to get a couple of jubilee clips to replace them with on re-assembly.

It's the pipe marked 4 on the ebay listing diagram.

Thanks for your help, I'll see if I can get one from the VW garage on my way home, if not I'll go somewhere else in the morning.