Unknown Part

[FamilyDub]

Gents, I need help................   

I have a problem with a rough idle/misfire cylinder 1.

The engine revs seem to be gradually lessening then the car will rev to about 2000rpm to compensate. Boost seems to be ok and I have no smell of unburnt fuel, so I'm guessing the fuelling might be running lean, but what might be causing this?

A bit more background:- I had a diagnostic done at an Indy garage and a replacement throttle body was deemed to be the issue, but this has been fitted and it hasn't fixed the problem.

I then asked for the coil packs to be rotated to other cylinders to check them, but this does not seem to be the problem either.

After my last service - at a franchised dealer - it was advised I needed an 'Inlet Manifold Pressure Control Valve' because the car was 'drawing air', for the sum of £110 inc labour... The Indy garage has categorically stated this ISN'T the cause of the problem, but can't find what IS...

When I asked my dealer what this valve actually was, no-one is willing to tell me and they have also flatly refused to give me the part number so I can find out off my own back... (Crow Rd, Glasgow, by the way  )

Does anyone know what this 'Inlet Manifold Pressure Control Valve' is, or recognise some of these symptoms?

I'd wager it was a dodgy DV or coil pack? Any help greatfully received....

[bacillus]

Does anyone know what this 'Inlet Manifold Pressure Control Valve' is, or recognise some of these symptoms?

I'd wager it was a dodgy DV or coil pack? Any help greatfully received....

I suspect the 'Inlet Manifold Pressure Control Valve'  is a long winded name for the MAF sensor.

Did the indie garage scan the car with VCDS and if so, did they supply you with the fault codes? This is the best avenue as the scan can pinpoint the fault.

Try disconnecting the maf and see if the car runs better. If it does then you've got a faulty maf.

[corgi]

Those symptoms sound similar to a defective IACV - idle control valve

[FamilyDub]

Try disconnecting the maf and see if the car runs better. If it does then you've got a faulty maf.

I'll try this

Those symptoms sound similar to a defective IACV - idle control valve

Interesting, and not something I've com across over the other threads or sites. I'll look further.

Any other opinions welcome........

[ub7rm]

I'm not convinced that these cars have an idle control valve as such but I could be wrong...

The problem sounds just like the fault I had on my mk4 which turned out to be the O2 sensor.  But could just as easy be the MAF as they both influence the fuelling.

[topher]

do a search for PCV .. fairly common fault. If it's leaking vacuum before the check valve then your idle will be all over the place. Fairly easy to diagnose if you know what to look for.. is your local independent a VAG specialist?

[FamilyDub]

If it's leaking vacuum before the check valve then your idle will be all over the place.

This sounds about right.

Is your local independent a VAG specialist?

Yes - an Audi Specialist that I picked up from friends on here:- 'A For Audi' in Clydebank. They thought it wasn't the PCV, throttle body or coil packs.