I had the same issues recently with my GT. The symptoms were intermittent; there was a period of no telling how it would behave regardless of temperature or any other factors. Sometimes it would fail to start unless held close to 3-4k rpm, but then a few minutes later it would be fine as if nothing ever happened. Sometimes there would be no power in 4th/5th when accelerating on the motorway; sometimes it would jerk violently when letting go of the throttle, even gradually.

I've had two Polo MK2F's now and have found them to be extremely reliable, even in 2015, as long as there isn't anything mechanically or internally wrong which doesn't involve electrics, like a blown head gasket for example.

Which leaves the various electrical components. Although robust and long-lasting, they're now over twenty years old at their youngest and will inevitably need replacing. The symptoms I had on my GT were the result of a combination of exactly: worn-out spark plugs, a faulty throttle position sensor, and a faulty lambda sensor. The individual symptoms of each faulty sensor can feel similar when driving, but are not exactly the same; and when combined it's like a 'perfect storm', throwing the ECU into meltdown when it feels like it. All these erroneous readings from failing plugged-in sensors.

The old spark plugs manifested straightaway in an intermittent misfire (the plug gaps were huge, renewed plugs = no more misfire); the TPS stopped outputting its signal voltage to the ECU midway through the accelerator pedal travel, resulting in ragged power-delivery at that point (changed sensor, no more judder); and the lambda (the worst culprit) got worse gradually over time, finally to a point where it was running dangerously rich - exhaust stink and black smoke with a juddery drive similar to faulty TPS and next to no power. This was found by comparing the drive with it plugged-in vs. unplugged - big difference.

I cured the spark plugs first, then the TPS via faulty multimeter readings, then the lambda by comparing the drive with it pugged in vs. disconnected. It's a different car now they've all been renewed - much more 'refined' with more predictable power and torque. Well worth doing if you're sticking with the 3F GT engine I think, and provides a good solid base for modding.

Also worth getting a code-reader, so that when you're plugging/unplugging sensors to isolate and compare, the ECU can run properly with cleared fault-codes each time it's done.

The spark plugs are only about 4k old and have just been gapped, coil and leads are new. Really at a loss with it. I haven't really got funds that allow for a code reader unless anyone knows of any cheapo ones that actually work!

I'm beginning to think it might be a loom issue causing the spark problem and then a cumulation of dodgy sensors causing the running issues.

It certainly did deteriorate and get noticeably worse day by day. Unplugging the lambda made no difference and neither did unplugging the TPS.

Is it possible to test these sensors with a multimeter?

I had similar issues with my 3f GT. 1991 coupe. Solved with a replaced lambda sensor. Had a mobile tuner out and used reader to identify fault codes. Sensor did not register on the fault code reader. Guy suggested this was the problem. It's now time to change as many sensors as possible with the age of the car. TPS is the next one. Changed blue and black water sensor already. Car is now smooth as.

Perhaps the hall sender on the dizzy is playing up - this post explains how to test it and the coil: http://www.clubpolo.co.uk/forum/index.php?showtopic=301901

The code-reader I've been using is a 'Vgate SCAN VS450'; they're around £25-£30 online currently. It shows and erases codes stored in the GT ECU at minimum, and has various additional menus for more modern cars.

To measure sensors with a multimeter they must be back-probed with a length of stiff hook-up wire stuffed down each terminal on the plug. The TPS I doubt would affect cold starting but to test: one terminal is ground; one is 5V supply or thereabouts; and one is signal voltage which sweeps between about 0.5-4.5V as the gas pedal is depressed. Any spikes or 'stuck' readings from the signal terminal can mean a worn-out TPS. I never probed the lambda plug, just compared plugged/unplugged.

There should be a significant difference to the performance with either unplugged. This is what I found with my GT when testing:

No TPS connected = less snappy throttle response, less power/rev pickup, it seemed less 'finely honed' and more sluggish. Noticeable difference.

No Lambda connected = less noticeable initially than no TPS. Less torque when pulling away from stationary and much less progressive torque delivery at partial throttle (cruising). Feels like a smaller engine. Noticeably easier to drive overall with a new one.

There's videos dotted around youtube of GT's performing 0-60 runs and acceleration demos with the camera aimed at the speedo/tach; a fair few of them aren't as fast as they could/should be, even in standard form.

Awesome, thank you very much mate. I'll get one of those scanners ASAP and test some bits and pieces. I'll post the results as I do it. Together we can fix my bloody car hahah!

I wouldn't mind one of those scanner things myself does anyone have a link please ?

You can also access live sensor readings and ECU fault codes with a laptop and diagnistic cable.

I got my cables off ebay:

You'll need this:

http://www.ebay.co.uk/itm/VAGCOM-USB-KKL-409-1-Cable-For-AUDI-Volkswagen-OBD2-Car-Diagnostic-Scanner-D1-/221769909565?hash=item33a284453d

and this

http://www.ebay.co.uk/itm/Brand-New-Audi-VW-VAG-2x2-KKL-2-2-to-OBD2-16-pin-Adaptor-Diagnostic-Cable-/110845760401?hash=item19ceec1391

Then get a copy of VCDS lite, or (even better but win xp only) vwtool

If you want to do some multimetering IIRC the autodata pages on GT and G40 is somewhere on the club g40 website

Disclaimer - The cables are off ebay, so if they are duff and don't work, it's at your own risk. Also my cables didn't work on a couple or early GTs (H-reg), this may have been because the their diagnostic port was not wired up. My cables have worked fine on many GTs and G40s however.

I've been back out and tinkered with it some more. I now have fuel, I have voltage to the coil and regained spark. However it still won't start. If I put my hand over the intake it doesn't feel like it's drawing in very much air.

Any more ideas?

I've just thought (as stupid as it is) does anybody have a diagram of the HT leads numbered from the dizzy?

Obviously I didn't have any spark before but I've since had the dizzy off so I may have put them back in the wrong order

Looking at the passenger wing, starting at the socket furthest forward it goes 1,3,4,2 in an anti clockwise direction. Number one is usually around the 10 O'Clock positon.

Awesome, cheers man. I'm hoping that will be the last problem on my list.

I'll keep the thread posted, I'll have a go tomorrow and see how it goes

Right I've been out to shout at it some more today and I've got no idea what's up.

I changed the rotor arm and tried another set of HT leads.

Timing wise, at TDC the rotor arm points to the lead for cylinder 1. IIRC this is right.

I really am lost as to why it won't start

Are you sure you're getting fuel and spark? Do you hear the fuel pump prime when you turn the key? Do you have plenty of power in the battery?

Yep got fuel and spark to each cylinder. I always charge the battery before I try messing around with stuff

Can hear the fuel pump prime when the key is turned and when turning the dizzy

When you crank it over does it attempt to fire at all or just crank and crank with nothing else?

If it is trying to fire you might want to get a helper to slowly move the dizzy round as you crank to try and find a sweet spot where she wants to start.

It doesn't even attempt to fire at the moment but it cranks fine

When you crank it over does it attempt to fire at all or just crank and crank with nothing else?

If it is trying to fire you might want to get a helper to slowly move the dizzy round as you crank to try and find a sweet spot where she wants to start.

Still no joy with it. Tried resetting the ECU today and that made no difference at all

How do you mean you reset the ECU? Did you hook it up to a code reader?

Are you still getting fuel and spark as you were before?

I was told that removing the battery and then connecting +ve and -ve leads on the loom for 10 seconds would reset the ECU. Yes, still getting fuel and spark as I was before

That's an urban myth that doesn't work in my experience even with these basic ECUs.

If you are getting fuel and spark the car should run. Have you tried rotating the dizzy as you crank the engine over?

Ah right fair enough, I am planning on buying a code reader/clearer but funds don't allow for one at the moment!

Yeah it should be running, hence my confusion. I have tried turning the dizzy while cranking but I haven't tried 180 degrees out yet.

My current thinking is that it isn't getting enough fuel. The fuel level in the tank is pretty low at the moment (not sure if that would actually affect anything) but my plan is to stick a bit of new fuel in and use some easy start to see if I can get some life out of it

Fresh fuel might help, I'd avoid using easy start if you can though.

Why would you choose to avoid easy start?

I've never found it has done any good apart from making an engine run for 3 seconds then die again. Plus all the stories you heard of it doing damage etc.

Really it should be possible to troubleshoot your issue and resolve it without the need for easy start.