Intermittent misfire at idle

I've been daily driving my 82 GTI, which has cold start issues as it is (revs drop quite a lot after being revved then pick back up again) but a couple of weeks ago the car started being a bit hesitant and spluttering from cold but cleared within a few seconds, which started to bother me a tad. Anyway, it seemed to sort of rectify itself a bit but one day I had to stop off at the pharmacy on the way home from work, car ran fine for a good 20 minutes to the pharmacy, went in got what was needed, had a chat with an old lady who couldn't quite believe the golf was 40 years old then started the car… three cylinders, yeah, thanks.. After just bigging you up too. So the mile or so to my house was a sort spluttery affair but only really at idle speed then clears and car runs fine, same again from cold the next day but it cleared after a few miles, then nothing for a few days then warm start at the shops it starts again. In the last few days it's been more frequent. Though Friday I drove from work 4 miles to supermarket, misfiring. Come out the shop start the car, perfect all the way home, missing this morning for a few miles again but nothing on the way home.

Interestingly it ran fine home today, switched car off, straight back on again and it started misfiring, so I turned it off and back on again and it ran fine again.

I've swapped plugs around, ht leads (miss is always on cylinder 1) but makes no odds so not those but given starting and stopping the car made it come and go I'm thinking a wiring/earthing issue?

The car has had I the last year injectors and lines, and at Easter a new ignition coil, plugs, leads,cap and rotor arm. Anyone got any ideas as to the best place to start looking wiring wise? Or am I likely barking up the wrong tree?

My GTI had a rough idle issue that I played parts darts with (new injectors, plugs, leads etc)

Was fine when underway buy rough at idle, tracked down to one cylinder and it was a leaky inlet fanimold gasket (no idea how it was fine for years and then leaked?)

At idle and low amounts of fuel the extra unmetered air made it too weak to fire, when driving at higher revs the extra small amount of air made no difference.

Wouldn't explain why its intermittant though?

Early-1800 parts darts sure is fun though eh

That's interesting regarding inlet manifold gasket, I changed mine last year and they are a bit of a swine, like you say though it wouldn't explain the intermittent nature of my problem

One thing I did notice is that the plug in cylinder 1 was slightly carbon fouled perhaps and that cylinder 2 was a glazed yellow colour, which as I understand could be due to ignition too far advanced or lean mixture. Hopefully I'll get some birthday money next week and treat myself to a timing light and maybe a compression tester, though given the misfire appeared then disappeared again through starting and stopping the engine (when warm) I think that's not likely to be the problem, I think it's probably electrical but I don't know lol it does stink a bit of fuel when doing it though but I guess that's inevitable

Bad Cap, or wire, and the plug looks oil fouled.
Have you checked for voltage drop on the ground wire From the battery to the frame, and then from the frame to the engine?

Briano1234 the cap is possible, new at Easter and it's a beru so normally decent but can't rule it out. I've swapped plugs and ht leads around and the problem stays with cylinder 1 so I think they can be ruled out. As for the plug, its not the best picture, I'll upload another I took. I'd have thought oil fouled would leave it physically oily? The plug is bone dry and more sooty a quick clean with a wire brush and looked new again.

No, I've not tried that, I was going to have a look at the weekend, but life got in the way of that. But checking earths was next to check

Looks like it's over fueled running rich. Swap the injector still connected to the line with its neighbour and see if the fault moves (they are not sequential so can go in any order)

Early-1800 worth a try, what would cause rich mixture on just one cylinder though? obviously could be injector but they're probably less than a year old and done 1500 miles maybe. Could it cause an intermittent misfire? Certainly could explain some of my cold start problems

Reading more about the yellow colour of the other plugs which suggest the plugs getting hot quickly during hard acceleration (which I don't do huge amounts of)

could be a vicious cycle were the plug is fouled and not sparking right which makes it even dirtier which makes it run worse and so on.

Clean them up give it a good itallian tune-up run

Trouble with a good old fashioned Italian tune up is the other 3 plugs will probably end up looking like this

Read you can use a colder rated plug to overcome this though plug no2 doesn't look nearly as bad as those did when I changed them last year, haven't looked at no3 and 4.

Will give it a bit though, then maybe look into different plugs see if it is advisable or not really on a dx

The misfire seems to have disappeared though for now, touch wood. Not done it since Friday. Will still check earths etc as advised when I get a chance

A guess, the fifth injector is closest to No1, if that dribbled a bit of fuel intermittently it wouldn't help.

I did wonder that, could explain why cylinder 1 seems richer than the others, but I'd imagine it would need to be leaking a fair bit to cause a misfire ? This misfire is so intermittent that it's not happened yet this week (touch wood) id have thought it would be more frequent if it was fuel related?

Hello, did you find the issue ?

@Andr�Sophian no, touch wood it kind of went away and hasn't been a problem since apart from the odd occasion from cold, usually when the car hasn't been started in a week or 2, and it only lasts a few seconds.

If it started doing it again I'd probably look into cold start injector first.

It'll start doing it again next time I drive it now, you watch..