Hi, I have a 98 wrx sti which has developed an intermittent hesitation! I've noticed it when on boost as well as sitting at 60mph (or slower) off boost! The car runs perfectly and I might only get the hesitation 1-2 times during a 2 hour drive.

Car setup: apexi power fc & boost controller, FMIC, dump valve, decat exhaust and turbo down pipe, tubular unequal manifold, walbro pump relatively new plugs and leads. My had the engine rebuilt around 2years ago and has been fine and is rarely used other than a weekend car now!

Any help would be appreciated?

 

Usual problem with hesitation is electrical.
Can you still read any codes stored? If so, do that first.

When mine did similar, it was ONE plug lead breaking down.

 

As above. I had the same problem. Turned out to be coil pack and leads.