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Another Gti rebuild starting issue

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Just spent last 18 months rebuilding a 1985 Mk1 cabriolet 1.8 Gti from a non running basket case. Car has been completely rebuilt from bare metal and now at the point of running and driving however I seem to have one of the very common problems with mk1’s which is starting and running etc. So to summarise…

Engine is a reconditioned DX code engine completely rebuilt
Fuel distributor re conditioned with new seals etc but none of factory screws touched
New cables
New fuel lines front to back
Tank was original but cleaned out and no rust
New vacuum hoses
New petrol pipe to tank
New distributor and leads
New spark plugs
New injectors

What isn’t new but put back on:
fuel pump ( can hear it working)
fuel accumulator
cold start valve
coil ( tested and working)

The issue I have is the following. The car will start on the first turn of the key when cold. If I keep my foot on the accelerator and revs around 1500-2000 it runs sweetly with no issue. As soon as I take my foot off the accelerator engine revs drop until it stalls. It is impossible to start again and just turns over. If I leave it for a few hours it will start first turn again and then stall if revs drop and again refuse to re start. I have checked there is fuel and spark and both are fine but engine turns over strongly but just won’t start. A mechanic suggested I look at the idle control valve or the fuel accumulator. Not sure it is the accumulator as I can see petrol nicely misting out of the injectors. Does this sound the right place to start? I am not sure what is the exact  starting process i.e. what does what in what order….

Any advice would be greatly appreciated as it’s getting very frustrating. As I say above I know there is both fuel and spark but once stalled it just will not re start until cold again.

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With hassle I had with mine being a pig
When I got down bottom mine it was fuel regulator warm up valve on side engine block   I changed everything nothing made difference till changed mine
But hey hope it help.

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Start back at the basics, check the timing marks on the cam belt, dissy etc. If you can post up some pictures.
If the cambelt is a tooth out to car will start and sort of run.
Are you using super leaded fuel?

Can you adjust the idle speed screw up so the idle is about 1500 rpm, will it run on its own with a higher idle speed.

Very last thing to touch or mess with is the mixture as you really need the car running to set it up on a CO machine…

Could be the mixture is very lean, when starting from cold the extra fuel from the 5th injector is helping starting/running and when engine gets some heat in it the 5th injector does not fire so that's why it's not starting?

1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.

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Sounds likes it maybe pulling air in. Brake servo?
Or maybe the WUR giving incorrect control pressure for a given engine temp.

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Is it getting fuel but won't start, are the plugs wet?

1983 MK1 Golf four door 1.8T 20V BAM remapped, MK2 dash and loom, TMI interior.  daily.

2014 VW California 5.1 with full Sportline kit, weekend home.

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Many thanks all that answered and offered advice etc. It actually looks like it was the fuel pressure valve (not sure that is the exact name) that screws into the fuel distributor. It has a spring and a needle valve with a couple of copper shims. I had split the distributor to change all the seals and metal gasket etc (I know you are not supposed to but made sure I didn't touch any of the factory screws and settings!) and it was dirty inside. I had no idea that the pressure valve was there. Haynes manual mentioned it and I thought I should check to see if any dirt was in there and of course there was corrosion and a few pieces of grit. A good clean out and the car fired up on first turn, idled fine, revved up fine and restarted after switching off.

It appears the problem is fixed..a real head scratch as there was fuel and spark, timing is perfect, new plugs, new injectors, new fuel lines etc

Thanks again for the advice.

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I made the mistake of assuming my woes had gone away! The car was running for a good 10 mins absolutely perfectly. Idling nicely and all seemed well the engine then spluttered as if fuel was starved and then stopped. Wouldn't start again until next morning when the engine was cold. Took ages to get started and once running it sounded rough. As soon as I take my foot of the pedal it then stalls and won't restart until cold again.

I took the WUR apart in case it was dirty and put new seals on it though it appeared clean inside. Now the car won't start at all. I have fuel at the injectors and spark but the car just turns over and won't catch. Any advice is very welcome.

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Just thinking out loud as it were.

If you have fuel and spark but no go then they must be being delivered at the wrong time?

Is it trying at all or just spinning over?

1983 MK1 Golf four door 1.8T 20V BAM remapped, MK2 dash and loom, TMI interior.  daily.

2014 VW California 5.1 with full Sportline kit, weekend home.

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As I say it was running fine then suddenly started running rough and then only starting when cold etc and now not running at all. It turns over constantly but with almost no sound of almost catching. I have checked timing etc and all is perfect. I was assuming either the WUR or fuel distributor is to blame? Fuel pressure as well as delivery seems to be an issue with these cars if I read correctly. What seems strange is that everything ran fine before this happened..

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have you checked the lift pump is working?

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I hadn't thought about the lift pump as I seem to have fuel etc at the injectors. Would an issue with that give the symptoms I have?
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