MK2 GTI 8V idles but when accelerator is pressed revs drop and cuts out??

Ok so its been fine,

Then I've started having problems, i can't even rev the engine if i do it splutters and dies.
First off i thought it would be the blue temp sender so i swapped it for a new one no difference.
I fixed a coolant leek on the coolant flange (knew this would make no difference but did it anyway)
Cleaned the throttle bay and the ISV (yes it vibrates with ignition on)
fuel pump primes and relays click etc
it does smell very rich though.
Then i thought it must be an air leak.. low and behold the capped off one just behind the head was broken (the hard to get to one) so i trimmed off the broken rubber and refitted it but sadly no difference.

I did un-plug the MAF and the car started to work and i could rev the engine as normal (albite some smoke came out the rear exhaust ) does this mean its an air leak? and i replace all the hoses ? or a bad MAF? i've checked the wires to the MAF and they seem fine

The only other thing that's happened before this trouble is the earth that connects the boot lid to the inside of the engine bay was broken. Its right next to the hinge top right (but i think that been like it for ages)


... any help is super appreciated

 

Sounds like dodgy maf, or possibly the throttle switches?

 

is it possible to repair the MAF? or is it a case of buying a second hand one?

 

It's usually a replacement. You could try take off the plastic cover and check for wear on the track. Have a good look at the plug first, that the pins arent corroded in either the maf or the plug, or wires broken.

 

spray WD40 with engine running and if revs even out theres air leek in system perished rubber

 

Its shouldn't run? that's odd then, so why when i unplug it does it carry on running? does that still lead you to think its a faulty wire to the AFM?. Then engine starts first time then idles ruff, if i give it some revs it goes to stall but then i stop and it recovers to idle (roughy ) if i unplug the AFM it runs and then i can rev the engine perfectly fine. when i plug the AFM back in the revs kick up a bit and it returns to a ruff idle.. i found a cheap afm replacement so gave it a shot and yes its still the same. I've read through your guide a few times and will go over it tomorrow.

 

Also where does the AFM cable go to? is it the fuse box?

 

just found this which looks like a good detailed way to check the AFM wiring

https://easyautodiagnostics.com/vw/1.8L/maf-sensor-tests-1

 

I would say it goes to the ECU.

 

Attached are couple of photos with part numbers on. Did a couple of tests, first i unplugged the ECU and the car wouldn't start. plugged it back in and it started. I then unplugged the AFM (black box on top of the filter) and it started but runs rough. If i unplug the AFM it runs but i wouldn't say its fine but it will rev without stalling, i haven't tried driving it.

 

This is where i'm going to struggle a bit. Can i test the loom from the ECU to the AFM wire by wire? my voltmeter skills are very basic.

 

Thanks John and everyone else for the help, i'll report back with what i find!

 

just a little update as i'm currently fixing some rusty areas. I decided to pull the ECU to test it and as i pulled the cables apart loads of water dropped out of the the plug. I pulled the plugs apart and saw a lot of corrosion on the contacts (pic attached). I've brought the ECU in to clean and opened it to make sure the corrosion hasn't spread to the boards, happy to say it hasn't. haven't tested since as its raining again but will let you know.

 

i was going to ask about it tbh. the main scuttle tray is the thin plastic one which has crumbled (looking for an alternative if you know of one) the deflector above the ECU is there not that its doing a good job. when you say scuttle drain do you mean the holes on the left of the ECU near the bonnet cable bung? if so they're clean.