Idle Misfire Help!!

[singh123]

Hi Guys I wonder if you can help (i know its not a mk5 but im sure you guys wont mind )

I have been experiencing a misfire at idle only I have logged each of the cylinders via VCDS and its showing a misfire on cylinder 4 but it doesn’t log an error when doing a scan. The revs idle at 750rpm and they stay there even when the car is misfiring i.e. the revs don’t move about.

The car driver’s fine when on full throttle and it doesn’t hesitate in rpm or misfire on load. But one thing I have noticed is if I use full throttle and build up boost to say 3500 rpm and then dip the clutch the revs fall to about 500rpm or so and then bounce up to about 1000rpm and settle at 750rpm.

I have replaced all four coil packs and spark plugs but the misfire is still there, so any help and suggestions will be helpful as is doing my head in

[winrya]

Took my car to votex today for a hesitation at 4k, he said he's just replaced an injector on a cupra. Had the same symptoms as you and replacing coils and sparks also failed before they got to injectors. Said something about an odd pop from the exhaust at idle.

[PDT]

find someone with VCDS near you and try a throttle body adaptation  (engine, measuirng blocks, block 60 and go. or engine, basic settings, block 60 and go.) Make sure the TB is clean by removing pipe from intake manifold and looking at throttle plate, clean with carb cleaner if dirty.

If this doesnt help, unplug the AFM and see if it runs any better at idle.

[singh123]

find someone with VCDS near you and try a throttle body adaptation  (engine, measuirng blocks, block 60 and go. or engine, basic settings, block 60 and go.) Make sure the TB is clean by removing pipe from intake manifold and looking at throttle plate, clean with carb cleaner if dirty.

If this doesnt help, unplug the AFM and see if it runs any better at idle.

Hi PDT

iv already had a throtle body adaption done one by awesome gti and iv done it myself aswell, il have a go at cleaning it aswell? Do you rekon i may have a split hose drawing in air?

Il give the sensor unplug a go, is there any way or finding out if an injector is faulty? The car dosnt seem to have lost power still pulls as normal i had it on the 1/4 mile at inters and it was performing well no hesitation or misfire

[PDT]

Also worth a try to identify the fault, remove plugs, clean them with carb or brake cleaner so they all look as clean as each other. Refit the plugs and let the car run at idle to replicate the fault for 10-15 mins and pull the plugs. If one is lighter/darker/dryer/wetter than any of the others then this could indicate the cylinder that is at fault.

[singh123]

I will try with the MAF out in the morning, i have just put 4 new coil packs and plugs in 2 weeks ago but the issue is still there

[bacillus]

fwiw here is a list of common misfire sources:

Bad or Incorrect Spark Plugs

Bad or Incorrect Spark Plug Gap

Bad or Incorrect Coil Packs

Injectors with high levels of buildup

Heavy buildup on valves

Bad or Incorrect Exhaust Valve Springs

Bad Exhaust lasher/rocker assemblies

Damaged O2 sensor

Damaged MAF sensor

Incorrect MAF housing

Heavy Turbulence over MAF housing

Bad or Incorrect High Pressure Fuel Sensor

Bad or Incorrect Low Pressure Fuel Sensor

Bad High Pressure Fuel Pump

Bad Low Pressure Fuel Pump

Bad or Incorrect Low Pressure Fuel Pump Pulse Width Modulator

Bad, Dirty or Incorrect Fuel Filter

Damaged High Pressure Fuel Pump Cam Lobe

Bad Evap Purge Valves

Leaking PCV system