My 1990 Legacy Wagon surges during acceleration and deceleration. It lacks the smooth, even acceleration and surges or "bucks" when accelerating or decelerating. It is worse when the engine has not yet warmed up, and seems that as soon as the temp gauge rises to normal operating temp, the problem clears up, for the most part. It also seems that when there is a load on the engine(even when at normal op. temp., going up hills or upon acceleration from a stop) you can feel it. By adjusting the position of the gas pedal while driving( give it gas and then let off some), it seems that I can get better/quicker acceleration. It seems to me that it is a timing problem. It's almost like it is advancing too much or not enough, and by letting the pedal off some while accelerating, it is letting the timing synchronize with the RPM's. Just a thought. No CEL's are displayed and no codes show up now. Any ideas???? Thanks in advance for the input.

TPS? Knock sensor? Air leak? Water temp sensor? ignition wires/plugs? fuel filter? -these possibilities come to my mind, but I am just guessing.

 

Let the real mechanics on this board answer this!

Fuel delivery. Start with filter, move on to the regulator (on the end of the fuel rail), and check the in-tank pump, too.

I have a similar problem. The fuel regulator is at the end of the rail? you mean after each injector? What could this be doing to cause this kind of performance?

Right side of the engine (from drivers seat), looks like a vacuum actuator.

I put in a tank of mid grade gas with a bottle of STP injector cleaner. It seems to running the best it has in a couple of weeks. When I saw that it was about $100 for a new regulator....whoa...try $2 gas treatment first.

 

I also tap VERY lightly on the exterior of the regulator to help free up any crud. It seemed to stumble as I did this and slowly got better as I went.