Ae92 Splutters 6000 - 7000 Rpm Help

[zuluae92]

hi i have a slightly modded 1990 rolla gti. as far as i know it has powerflow exhaust from cat back, piper x filter, chiped with a superchips box too, and poss an ingnition advancing box.( not sure there seems to be a blue box attatched to the ignition not sure wot it is). the engine seems strong and pulls hard, it really takes off at 4500 - 5000rpm. but then just when it seems to be getting to its best it will start to cough and splutter always between 6000 and 7000 rpm. if i do keep my foot planted then it will gradually but annoyingly build up whilst shanking me about. it will only do this whilst under load ie in gear, when in neutral it will rev all the way to 8500rpm with ease. which is annoying as i am loosing around 2000rpm of power.

was wondering if a simple dyno tune would solve this or if something else may cause this

please any advice or fixes would be greatly appreicieated

[Twincam.GTi]

Possible ideas:-

One of the three wires going into the MAP Sensor (black thing mounted on bulkhead behind injection unit area) has cracked/broken - they are tiny!

Tube perished that runs from map sensor into pipe mounted on injection unit

Distributor - is there much of an oil leak around (due to o ring seal wearing) -and they all usually suffer this! If so if it bad (e.g. is distributor sat in a 'mass' of oil?) if so oil could be drawn inside and inside cap area thus 'tracking' under extreme load/power.

Just a couple of thoughts, sorry

:(