Rough/hunting idle, coil dying?

[rgvlee]

I'm after a second opinion on a recent issue that's come up
Over the last couple of weeks on startup the engine has started chugging occasionally. Once warmed up all fine.
No codes etc. Didn't think much of it it wasn't constant just every now and again. Wasn't like it dropped a cylinder just the odd misfire.

Today the issue has started occurring all the time at idle.
Rough idle (like a lumpy cam), rpm hunting between 750-900 rpm and occasionally if I coast to a stop immediately after I get off the gas the rpm goes up then slowly comes down.
Otherwise car drives fine you wouldn't know there was an issue.

I pulled all the plugs tonight (bkr7e gapped to 28 thou, 2500kms on them) and one was no like the others. Nothing major but noticeably different. I suspect I may have a misfire on this cylinder. I've popped in the pre-service plugs and the issue remains. I've swapped the suspect cylinders coil over to another cylinder but I don't really want to drive it much to see if the issue moves.

Anyone had a coil fail over a period time? I've had them go on my previous polo but they just stopped working one day there was no gradual decline.
I've still got all the sai connected, does that affect idle after warm up? I wouldn't know if it's throwing a cel as it's been coded out of my tune (and I have been lazy about removing it all)

[sambb]

do you have vcds? it sounds like a vac leak but that wouldn't affect just one plug position. if you can borrow a coil, you could shuffle them one cylinder at a time and see if it clears. shuffling a potentially bad coil will just move the fault to another cylinder and you'll get the same symptoms.

[h100vw]

Does sound like an airleak to me. The revs staying up until the ECU has time to adjust itself for the extra air. Still got std DV? Boosts ok otherwise?

VCDS would be handy.

Had a flat battery recently?

[rgvlee]

I too suspected air leak with the rpm going up when throttle closed but I have detected a bit of unburnt fuel smell.
It doesn't do it all the time.
The idle is all the time.

Other than idle drives same as always. Boosts hard still.
No vcds. Will an ebay cable do?

[h100vw]

I too suspected air leak with the rpm going up when throttle closed but I have detected a bit of unburnt fuel smell.
It doesn't do it all the time.
The idle is all the time.

Other than idle drives same as always. Boosts hard still.
No vcds. Will an ebay cable do?

As long as it can read fault codes and see measuring blocks. block 032

[sambb]

in the mean time check all the fuel vapour return and crank case breather lines and anything else thats easy to check. Listen for hissing at idle and spray crc on anything suspect. The revs should jump if it sucks it in. cos your combustion on cylinder may be suspect maybe give that cyliders injector seal a squirt.

[seangti]

Other than idle drives same as always. Boosts hard still.
No vcds. Will an ebay cable do?

You'll need the blue obd cable from ebay. Don't install the drivers that come with it as they are for Windows XP. I put a post in the VCDS section with links to the latest drivers going back quite some time now. You most likely will also need to set a com/serial port to a USB manually. Only takes a few clicks to sort out.

Use the free VCDS version to make sure it all works, that you can check measuring blocks and scan. The free version will be near useless for what you need at the moment as it gives very limited measuring blocks, not fuel or boost that you need at the moment. You will need to pay for the "lite" version which was around the US$99 from recollection which will give you access to what you need and auto scanning, ability to adjust/reset stuff.

The blue cables only work for our older ECU's (ours and mkIV's), they aren't canbus so won't work on a mkV or newer. Or pay for the full VCDS version at US$250 and you can do anything/everything.

[rgvlee]

It's the elm327 cable we need right?
USB Cable OBD2 ELM327 CAR Diagnostics Scanner Software Support 64 BIT System G | eBay

Also missed the battery question. I have fitted a new battery probably about 6 months ago.
The fuel smell is from the exhaust not the engine bay.

[Lucas_R]

^ Those ELM devices are pretty basic. And no doubt thats a fake ELM unit for $10. I have a genuine ELMScan and its still very basic compared to VCDS.

Ive also got a fake/copy VCDS cable and software you could buy if you want it. It works fine but you cant update the software (its version 11.11) otherwise it will stop working. You also cant use it with WiFi connected otherwise it will try to update the software automatically and stop working.

With the Polo GTI 20v being an older car, the old software version wont be an issue for you - but you just need to be diligent to make sure you dont try to update the software and dont have WiFi connected on your laptop when you use it. $25 incl postage and you can have it. I used it for 18 months or so on my Mk6 Golf R and never had an issue (does coding changes/error codes/measuring blocks etc etc)

I ended up buying the genuine VCDS cable as i was doing some coding on 2014/2015 model cars and the older software on the fake cable wouldn't allow me to make the changes i needed to do.

[seangti]

Just type in vagcom to ebay, they are the 409.1 KKL OBD I have and was referring to. I have no experience on the ELM stuff.

There are also silver cables with the FTDI chip, I have one, but it gives a very slow refresh rate in VCDS. I can't recall if it worked at all though... However, I needed the FTDI cable for logging in ME7Logger and for uploading tune revisions. For VCDS, use the blue cable. If you're running ME7logger, get the silver cable.

ME7logger doesn't scan for codes or provide fuel trims, etc like VCDS. So for your current situation VCDS is what you want to run. ME7 is a brilliant logger (unlike VCDS).