Check your ignition coils, and / or your TCI (black box).
The TCI is now 30 years old and also the ignition coils that dissolve slowly by showing the temperature differences.

try also to change the ignition coil of wire to spark plug. Do not buy expensive cables, just buy a cheap makes less problems.

You can also use external coils, must have 85 ohm output to the spark plug in which brand does not matter

Attention, the TCI may, it does not work if you can not plug the polls on mass.
Can then quickly pass a defect.

Problems 3000Rmp is often a problem with TCI have had many here.
You press the thumb  

Fixed
Swapped pick up coils even though old ones tested ok and swapped alternator old one had burn mark on 3 pin plug
Runs fine now