I bought a 2002 wrx recently. The previous owner put on some after market parts. Exhaust, radiator, intercooler, and others. The engine sounds like it was misfiring, but after a little look and taking off the intercooler hoses I found that exhaust gas was going into the intake manifold. What could cause this, and what damage could have been done to the engine with this problem.
Thank you for any help.