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Really Bizarre Engine Problem

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Hi All,


My N/A Legacy has developed a bizarre engine problem over the last few days. It seems to only happen at highway speeds, and not under acceleration. The car doesn't want to stay at a steady 65-70 MPH. I can't tell if it's surging or losing power, or both.


For instance, I'll bring the car up to 65, and if I let my foot rest on the pedal the car will accelerate for a second, then slow down for a second, then run fine for 5 seconds, and then the accel/decel will start over. Sometimes it just accelerates, sometimes it just looses power.


It doesn't throw any CEL, and the problem doesn't seem to happen when I'm driving through the city.


There is one other kinda strange thing the car does. When it is idling, it will keep a constant RPM, then every 15-20 seconds the RPMs will jump a few hundred, then come right back to normal.


And thats not the most bizarre part. The engine can keep a constant speed when I have cruise control turned on. I was going to check all the obvious things like plugs, filters, wires until I put it in cruise control and saw it operating flawlessly.


Are these cars drive-by-wire?

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Well, there are several things it could be. Maf, O2 sensor, plugs, wires.


At 100k, plugs should have been replaced 3x, wires at 100k arent a bad idea either. We have seen several cars exhibit similar problems and it was a dirty maf and/or O2 sensor.


When you have the timing belt done, i would have the mechanic check it out.




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