Mk1 Cupra Boost Problem - Searched but cant find info.

[sion_kwl]

Hi Guys,
I have done many searches but not found exactly what I'm after..
Picked up a very cheap Mk1 Cupra last week (AUQ) and it has an intermittent boost issue that I just haven't been able to diagnose.

The Car:
AUQ engine, Remap (unkown origin, supposedly 240bhp), FMIC, Cone filter, Toyo-sports cat-back
Coilpacks, Turbo, MAF recently replaced, N249 removed.

Symptoms:
When under medium to hard throttle, 3krpm onwards (full boost I'd guess) it hesitates through the rev range, it's quite jerky, and produces a backfire.
Does not happen constantly, sometimes it will pull the entire rev-range fine, and it is very quick and very smooth.
I pulled the plugs and there's evidence of rich running, I have replaced the DV and checked for boost leaks and have drawn a blank.
EML codes are for N249 delete only. no flashing CEL when the problem occurs, and no limp mode.

My guess for now is the N75, but I thought I would try and get some more experienced opinions first. never had electronically controlled boost before!

 

[sion_kwl]

In case anyone's looking at this, I actually solved this with new plugs. old ones looked fine when I'd cleaned them but I guess you never can tell

 

[GilMastaG]

Was there any oil on them? I have a similar problem and my forth plug well has oil in it....got to find out why and how to fix it = /

 

[GilMastaG]

I found putting half a tank of high octane fuel really helped with performance, I been putting some thought to.decarbonisation, big john said it worjs wonders

 

[Bigjohn84]

Was there any oil on them? I have a similar problem and my forth plug well has oil in it....got to find out why and how to fix it = /

Oil on ur spark plugs mean the inner gasket is prob leaking and oil is getting down into the cilinder, take ur coils out one by one and look down the hole with a torch, if you see oil in any of them then it looks like the gasket needs changed inside the dam cover.