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99 dohc auto idles good but stumbles and dies on acceleration

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I have a 99 Outback with a 2.5. I had pulled the motor and replaced head gasket and timing belt and water pump. Reinstalled and it ran good. Then I decided to install half shafts and front brakes and rack and pinion boots. I disconnected the battery so I could unlock the wheels to do the half shafts. Got everything together and now it idles great until you try and accelerate and it stumbles and has no power and sometime it dies It is not drivable. Out of gear if you move the accelerator slow you can rev it up and it does not miss. Any help would be greatly appreciated. And no codes.

Bob T

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Might be worth checking vacuum lines for leaks, etc. Older hoses can split, rot on a bend, harden on metal nipples causing a loose fit, etc.


If it won't idle smoothly in gear and keeps stalling, might wanna inspect your EGR (I assume yours has one but dunno enough about that year). It might be stuck, vacuum line to it is loose/broken/leaking, etc. The diaphragm can become faulty with age as well causing it to fail, or excess carbon/gunk might be messing with it's operation.


Idle air control valve sticking? If the engine is cold, does it kick up to like 1500 rpm range briefly, then slowly drop to correct idle? Or does it start and hang at normal idle? (cold engine). Might be worth checking it's properly connected, not gummed up internally, etc.


Double-check your battery connections. Although not seemingly as common as it used to be, actual battery clamps can corrode internally, inside the crimp, leading to issues. I had an '84 Chrysler Laser 2.2L turbo that actually picked up some power after replacing the clamps as the factory ones were that bad. Since you messed with your battery briefly, it might be worth inspecting the area for breaks, bad grounds, etc., especially since you are not getting codes yet.


These are all guesses on my part as I'm just a back yard DIY'r. Hard to guess w/o codes and car in front of you. You might even have something as benign as a failing fuel pump. I've seen some over the years cause stalling, but start back up, to eventually erratic starts that stall when trying to move.

Edited by Bushwick

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^ I had that issue with my EJ22 - but it'd only do it in certain temps once the drivetrain was nice and hot :/





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