Engine Performance problem
1994 Subaru Liberty 4 cyl Two Wheel Drive Automatic 110000 miles
For the last year my car has been having an intermittent issue going up hills. What will happen is that sometimes half way up a hill the car will rapidly loose power, engine makes a put put noise, revs wind down and it crawls unhappily to the top of the hill. Once stopped at the top of the hill it (usually at a set of lights) it will shake quite roughly. If I put the car in neutral and keep the revs up a little the shaking stops.
5 minutes down the road the car runs fine again.
At other times going up hills the engine pings
Now I have replaced over the year the air filter, the fuel filter and the fuel pump / mesh filter to no avail and I have just checked the fuel rail pressure which is within spec (30psi increasing to 40 psi when the vacuum hose is removed from the regulator). And to cap it off for the last 6 months I have been running the car on 98 octane in the vain hope it may help. None of this has fixed it, sometimes it goes away for a month only to come back worse than before. Any help would be greatly appreciated.