86 gti idle issues !!

Hi all, hope someone can help me with this one !
On my 86 cabby gti im having idle issues !! One minute it will tick over at 1000 rpm and the after a blip of the throttle it will start to stall.
Other times it will tick over till I try and and turn the lights and blower on and then it will try and stall again.  
This is driving me nuts !
I really hoping that I am not the only person who has had this problem ?
 I have tried different tci units thinking this might be it but I am running out of ideas now lol. Sounds like its not always firing on all cylinders. Leads dizzy cap ect are all newish. Basically a new engine as well !!
I put new injectors in but cant see that they would be an issue ???? Helllllllp !

Have you checked and tuned the mixture? Sometimes if its wrong, then idling can be all over the place ie can't be properly set. I can't remember which direction but one way (rich/lean) "damps" down the idling variation so its very gentle, and the other way makes the revs bounce up and down more than they should.

Since there's a range of acceptable idle mixture settings (which don't really affect mixture at higher revs/load) you can tune it to one or other end of the scale and get a decent idle that way.

Hi paul ! Sadly I dont have a gas tester to check the mixture. Weird thing is I haven't touched it so it would be strange for it to go out ?
It seems to be electrical load that is causing the idle to drop ?? When the cooling fan kicks in it drops, same with the blower and lights. This fault has just suddenly developed in the last few days ???
I did find that the blower fuse was 30 amp and melted a bit where it should have been 20 amp in there. Hopefully its not melted wires behind my dash, going out to check now… fingers crossed lol.
Cheers paul !!

Yeah it just sounds like the idle speed is really sensitive to load. It will dip a little with electrical loads on/off but shouldn't do it to the point of stalling etc.

The trouble is that the fault is intermittent. One day the car will tick over lovely and another day im left foot braking up to junctions to keep the engine running !! Was meant to be doing my clutch this weekend but that seems pretty pointless if the car wont run properly...

Just tried swapping the battery over in case that was at fault but still no joy.
Pulled the plugs from the fuse board and no sign of burnt wires or corroded pins ect.
Could it be the ht leads ??? They are newish but only cheap motor factor ones ???
I do have a spare alternator loom so may try that…

I still think its the mixture, and you're chasing your tail looking at electrical stuff.

You maybe right paul ! The car is meant to be going on the rolling road soon but the mot will be first. Will just have to hope it passes otherwise I'll be getting the bus to work lol. May as well crack on with the clutch as im getting no where with this haha.

It would pay to check for any leaks on the air intake. Mine was a bit like that when I first got it running. Mine had stood for 8 years and had fuel issues but my idle was all over the place once I had sorted these. I could get it ticking over nicely but after a rev of the engine it would suddenly be nearly stalling or ticking over high, the engine would nearly die if I switched on a few electrical items! Lots of places that I had leaks including vacuum advance pipes, all the breathers, mfa hose if fitted and brake servo hoses. Good luck.

Cheers saulty, booked in for the mot on Wednesday and they are going to tweak the mixture for me at the same time.
Im going to go over the vac lines ect one MORE time incase ive missed something… lol. On the plus side my k&n air filter finally arrived today !! Its the little things !!

Well my situation has gone from bad to worse drastically.
On my way back from work the engine revs began to rise on there own up to about 2k. Luckily I was nearly home so trundled back. I checked the throttle body and it was properly shut. Started the engine again and the revs shot up followed by a dreadful metalic sound so switched off immediately. Whipped of the sump incase a con rod ect was failing but all was good. I decided to turn the engine by hand only to realise that it would no longer go past tdc on cylinder 1. I fear that somehow I have bent/dropped a valve…. no good on a big valve head…
I have another standard head I can put on but its not worth it untill I can get to the bottom of the cause.  Im thinking that the metering head failed causing a severe lean out of fuel creating to much heat in cylinder 1 making the valve stick and then hit the piston. Not had to rocker of yet as I was fuming a thought it a good idea to walk away lol.
Does my diagnosis sound plausible to anybody ?

Its possible but I've never heard of a metering head actually partially fail, so that it severely leans out the mixture. There's plenty of ways (and instances) where something in the fuelling completely fails and stops the engine. It would have to have been gradually failing over a long period of time to lean an engine out to the point of letting it burn up - normally its noticeable on the temperature gauge, and non-racing driving isn't severe enough to break the engine like this.

I suppose its possible that it was always marginal and the valves were on their way out, but a valve doesn't normally just "stick", it would get harder and harder to move resulting in its not closing fully and this would be noticed in rough running. Or a spring or collar etc fail.

I think what's more likely is there is an air leak somewhere which raised the revs, and there was an assembly error or component latent defect which meant the valve's life was short lived anyway. Or it might just be that the cam tappet has failed? Its difficult to say without having heard the engine running or heard the metallic noise you have.

If the engine cannot be turned over you may as well remove the head since it will probably reveal the issue. If there's no issues there, then it will cost a head gasket.

Its a bit weird that the engine was running but now subsequently can't be turned over with a bar. If something fails catastrophically, it would seize the engine while running, and if its going quickly in gear, the disrupted components would normally break the block and put a hole in it or crack the block to eg allow something loose to flap around.

As said, without all the info you have its a bit of a guess though.

I forgot to mention the suspected failure happened on the driveway not at road speed so at least the bottom end was saved. I shut the engine down as soon as I heard the noise. When I get back from work tmw I'll start stripping down the top end and see whats what.
I think your mixture/fueling idea was right paul !!
The head was in good condition when I bought it but It could be possible that something failed.
Definitely have to get another metering head as I dont trust this one anymore.
Really hoping to get to the agm this year but it'll be a push now.