Annoying flat spot, no immediate start from cold

I have an 85 1.8 gti cabrio.
Fuel tank cleaned out, new lift pump with seal replaced and Bosch fuel filter on its way
At the turn of the key it does not fire up immediately, need to pump the accelerator a few times to get going, then stutters a bit
Once idling I have flat spot if I rev or blip the pedal

Last time I’ve been on here was 2009 when I had much fun in a Mk1 G60 ( how time flies )

What should I look for, change or make adjustment to
Would be good to have a process of elimination
Where would you start

Any help appreciated

Do you wait for 5 seconds after turning the key to run, before you then turn the key to start?

If your fuel pumps aren't allowed to pressurize the system before you start your car, it can hesitate as the fuel pressures aren't there.

So try, key in, turn to 1st position, wait 5 seconds, then start your car.

What's the CO? Mot should tell you this.

It could be a few things which are causing your problem

Leaking fuel injectors,
5th injector not working.
Thermo time switch not telling the 5th injector to work
WUR faulty,
Plunger in metering head sticking.

How's the ignition system, is the dissy cap, rotor arm, HT leads, spark plugs all new and are you getting a good spark.

How olds the air filter?

You should not need to keep pressing the accelerator pedal to start the car.

Can you smell fuel when it starts?

Briano1234 said

Do you wait for 5 seconds after turning the key to run, before you then turn the key to start?

If your fuel pumps aren't allowed to pressurize the system before you start your car, it can hesitate as the fuel pressures aren't there.

So try, key in, turn to 1st position, wait 5 seconds, then start your car.

I would sometimes wait to hear the fuel pump but i've tried that now and still a sort of stutter when i rev slightly, this is from idle speed.
If i keep the revs over 1000rpm then no flat spot

mark1gls said

What's the CO? Mot should tell you this.

It could be a few things which are causing your problem

Leaking fuel injectors,
5th injector not working.
Thermo time switch not telling the 5th injector to work
WUR faulty,
Plunger in metering head sticking.

How's the ignition system, is the dissy cap, rotor arm, HT leads, spark plugs all new and are you getting a good spark.

How olds the air filter?

You should not need to keep pressing the accelerator pedal to start the car.

Can you smell fuel when it starts?

No Fuel smell, i replaced the lift pump and seal as there was dirt, bits of rust in the tank
Tank has also been cleaned out, lift pump was very noisy anyway

I've made a note of the above list, a good process of elimination, once i go through will update on this

cheers

Remove the 5th injector (it's at the end of the inlet manifold) be careful with the paper gasket and try not to rip it or you will need to make another one out of a cereal box. Put the 5th injector it in a jar and with a cold engine try and start the car, the 5th injector should spray some fuel when cranking the engine over.
With this test you can eliminate thermo time switch and 5th injector.

mark1gls said

Remove the 5th injector (it's at the end of the inlet manifold) be careful with the paper gasket and try not to rip it or you will need to make another one out of a cereal box. Put the 5th injector it in a jar and with a cold engine try and start the car, the 5th injector should spray some fuel when cranking the engine over.
With this test you can eliminate thermo time switch and 5th injector.

Spot on,  will try this thanks 🙏