1.8t very rough idle/miss

[Jarred]

as i've discovered recently, any small vaccum or air leak, can cause havoc, so I vote MAF, if not that O2 sensor, then depending on the work you had done, all the new joins/seals are all sealed up tight!

[Golf Loon]

Ignition control module very common on these cars. Wont show a code, or will show up as coilpack

I have a test unit if you come past. And can get you a new one lots cheaper than VW

[FknDubbin]

Haltech aftermarket ECU/computer

Yes it can also be done to your's using the oxy sensor and knock sensor to calculate the air/fuel ratio etc.

You still need to calculate the amount of air entering the engine. im guessing Haltech uses a manifold absolute pressure (MAP) sensor instead of a MAF sensor.

[JustCruisn]

I had a vacuum leak in mk mk4 and the idel was way rough. I found a hole in the pipe which runs from the throttle body round to the brake booster. A quick patch fixed this up.
Also APR chpped 1.8Ts can have a rought idle when the aircon is on, pretty common but not as rough as a leaking hose.

[torque]

Faulty maf; O2 sensors don't cause rough idle

[SoVeReIgN]

With the MAF disconnected it runs MUCH smoother but still not perfect.
Also feels alot smoother accelerating too - I'll give mine a clean and if that doesn't work (didn't last time) i'll have to source another replacement.

Damn.

Golf-loon - Do the audis have the ICM ? Is that the one that sits in the airbox on the golfs?

[gpk_gti]

on the side...

remember vw do a exchange service...pm william,maybe he can get u a better price like he did for me.

[ranton-inc]

Check MAF

Check Ignition Module Thingy (connected to side of airbox)

make sure your air hoses arent leaking MKIVs are prone to Boost/Vac leaks

check your downpipe is bolted to turbo correctly

check O2 sensor.

[balkanac]

Is there any info anywhere on how to realign the trottle body?