trying to solve a problem with engine bucking in 2000 Legacy

[996TT]

Hi and thanks for looking.

I'm not sure if anyone has ever had a problem like this before, but my brother's 2000 Legacy brighton has been having this weird bucking problem for quite a long time now. The car had pretty high mileage, so we recently swapped the long block with a lower mileage one with about 80k on it. While we were there, we changed the timing belt, tensioner, gaskets, coil, PCV , clutch etc.....we reused the original intake plenum..but purchased a new IACV hoping it would solve the problem....So even after all this the car is still bucking while coasting in any gear using light throttle......what happens is while driving in say 5th gear, while the throttle is depressed enough to keep the car at a constant speed, it bucks for a second causing the motor to rock violently back and forth, then continues on as if nothing happened.......it happens randomly . Checking for codes, the only thing I've seen is something to do with the "EVAP system" ...

If there is anyone that has ever gone through something like this before, please let me know if you have any ideas....

thanks in advance

[Huffer]

Was the clutch in good shape when you put the new longblock in?

[996TT]

the car was doing this before the engine was changed. The clutch is new now.

The car just loses power then comes back to life, it sometimes does this a few times before you have time to lift off the gas and then re-apply the gas....the it goes away until the right conditions occur to make it do it again

[jey]

what happens is while driving in say 5th gear, while the throttle is depressed enough to keep the car at a constant speed, it bucks for a second causing the motor to rock violently back and forth, then continues on as if nothing happened.......it happens randomly . Checking for codes, the only thing I've seen is something to do with the "EVAP system" ...

If there is anyone that has ever gone through something like this before, please let me know if you have any ideas....


A bad EVAP solenoid can cause this - happened to me. You can test this easily by disconnecting the vacuum hose between the solenoid and your intake manifold and plugging it up and see if the problem goes away. That's my current solution because I don't feel like shelling out for a new one.

[996TT]

thanks for the reply jey...sent you a pm