Completely stumped

Hello to All

We have a mk1 cabriolet from 90/91 (LHD). I had to use the car as for my commute for a couple of months through the winter until I'd got a cheap runabout. I parked the mk1 up in the garage where it stood for a couple of months, when I came to use it again it would fire/start as normal then die. It stayed running eventually but then tick over kept increasing (and staying increased) every time the  accelerator pedal was tapped so I would have to shut it down. When it did seem to be ok I took it out onto the road for a short spin but on numerous occasions it died again. Left it for a couple of weeks now tried it again and it starts fine but then (without touching the accelerator pedal) revs itself up so hard so I just shut it down. Tried numerous times, same revving, until finally I started it, clutch dipped, in reverse and as it revved again slipped the clutch to back out of the garage and half way out the revs dropped of their own accord to normal tickover??!! and I moved the car and parked it up outside the garage.
It all seems totally random, at first I thought the accelerator cable had become frayed as that is what it seemed like with tickover rising every time the accelerator was blipped, don't think that is right now though as revs up from tick over without accelerator pedal being touched.
I wonder if it could perhaps be the simple computer box (not sure of the name) having had some issues with (or now effects from) dampness from car being used in winter then left for a couple of months.
Any suggestion are greatliy appreciated, it's all totally flukey when it runs so no rhyme nor reason to it. Have no idea where to begin as one minute it seems ok then stalls or revs start racing.

Thanks beforehand  

Is it a carb or a GTI?

If it's a carb model it could be that the wax stat is playing up.

Alternatively it could be an electrical fault. Might be worth checking all the wiring connections around the carb and from the control module to the ignition and carb.

Ian

Hello
Thank you for your reply.
It's fuel injection.
I'll have a look see at the electrics, hopefully something will be obvious!

Update!
I have just been out in the car, started ok but bit rough then settled down to normal tickover, left it for a while so decided to give it a short run along some quiet roads. Drove fine for a couple of mins then started reving and dying, reving and dying (dropping back to tickover) so drove it back home ok but not running normally ie the tickover is up and down, got back to the house and it sat for a couple of minutes with tickover normal then up to 2500/3000 rpm (by itself, not me doing it) slowly dropping in revs until eventually it settled back to normal tickover.
Anyone ever experienced anything similar or got ideas what the probs might be, I would love to hear them. It's a 1.8i and here is a photo of the engine. BTW while driving it, when the tickover went high I would blip the throttle to try to clear it but it doesn't the revs just go higher?!
Thanks again for any help
Richard

Well the 1.8 digifant, Hates Vacuum leaks

There is also the issue that the blue CTS sensor can cause lumpy reading and as it is only @ 9 bucks usd replace it and the o-ring.  On the back side of the throttle body is the idle bypass screw 7mm and brass if you can turn it with your fingers then the o-ring is shot and it is leaking air.  Count the turns to remove it, then write that number down, replace the o-ring with one from your favorite hardware store and return to the count that you wrote down.  Cover the threads and the threads of the screw only with Teflon tape.

Check the static timing of the engine easy to do with a DVOM.  No timing light needed.

Static Ignition Timing on VW A1 and A2 DigiFant Engines.

Vacuum leaks and the CTS sensor go a long way, but the last best piece of advice I have it to replace your battery to frame and frame to engine grounds…. The Digi hates bad grounds… You can use two off the shelf cables to replace the single. and at the frame connection under the AIR BOX.  clean it with a wire brush, and after attaching the 2 cables spray it with battery corrosion preventative spray paint.

Vacuum leaks.
CTS sensor
Grounds…..



Notice that I didn't mention the missing radiator cards, or the stray wires that are lurking about.  Also the Farging plastic outlet flanges and bits.

in the Archive section I have a list of how-to's on the 90ish digi cabriolets see the link in my tag line on the signature…

Briano1234
Thank you very much for the advice, i shall work my way through your suggestions, thank you!