Hey guys my brother is having a problem with his car, it is a 94 ST205 Celica GT4 WRC. We imported it a year ago and had no real problems with it. But now its got a massive hesitation when the boost.
Its weird, when the car is cold it only boosts a little (pretty sure its ECU controlled) and no problems, but when it warms up and it sees hard acceleration and boost the stock boost gauge goes all the way to the top of the guage and there is a massive misfire/hesitation. The car basically starts bucking. I changed out the plugs (pain the ass with top mount water to air intercooler), and the plugs looked a little dark, but otherwise fine. The distributor cap and rotor looked fine too, plug wires look new.
The only think I can attribute the change to is that a few weeks ago, regular gasoline was put into it by accident. I first noticed the hesitation a day or 2 later and 1/4 tank had been used. I dumped some octane booster in it and some 44k fuel system cleaner, but no change.
The car drives perfect under light boost and is still driven daily, and isn't throwing any engine codes. When the hesitation happens it also doesn't throw the check engine light or anything. No smoking or anything weird either.
Any ideas?