2001 Legacy low speed hesitation

[Zoltan]

I have a 2001 Legacy EJ25 automatic with low speed hesitation problems. Car is new to me and has 130 000 miles on it.  It does look like it was in a bit of a fender bender and had a front fender replaced. I looked underneath the car and it does not look major. Car was giving codes for 3 missfiring cylinders. I changed igintion coil, new NGK plugs and wires. Codes are now gone. Its better, but hesiitation at low speeds is still there, sometimes it will make a poping noise once or twice (backfire I think). It was cold this morning (40) and she stalled out for the first time, so the cold does seem to make it worse. I have searched a around and some say to change the front O2 sensor even though no codes and some say to check  grounds.  I am checking the grounds but I just want to know if anyone else has any additional experience or  thoughts on this?  If someone can tell me which grounds to check that would also be a help. Electrical work is not my strong point but I guess I will learn!  Thank you for your time , it is much appreciated.  I

[montana tom]

vacuum leak or the timing off a tooth,    both come to mind. 

[1 Lucky Texan]

yep - def check timing.

 

I wouldn't rule-out a 'dropped' valve guide or burned valve.

[montana tom]

Burned valve and it would be shaking at idle ,  most likely show a misfire code. Compression test would show that.

So far in over 30 years messing with subarus and I personally have not seen a dropped guide, even when I was dirt circle track racing and seriously over reving at times, the heads always held together... more than I can say for a few pistons though .  

[1 Lucky Texan]

there's at least 1 video showing dropped guides. I think a car has to have been quite neglected to have that happen though.

[1 Lucky Texan]

re-read the post, the backfiring kinda points to some timing or maybe valve issue - I suppose over-fueling might be an issue too but????

find the tooth count for the engine on-line. Bring the marks on the pulleys around to the timing points and do a tooth count.

 

here's some wild ideas;

 

one thing that will kill power often with no code is a bad knock sensor, easy cheap to replace too.

although it seems to be a rare failure, the car has 2 temp sensors, the gauge part can be good, but the ECU uses a different sensor (in a single unit on some cars) to determine if a 'choke' condition is required and if bad, might not be supplying enough fuel when cold? or too  much when warm?

another easy thing that will mess with idling - the IACV tube under the intake tubing could be cracked/loose.

dirty throttle body might cause idling problems.

Edited October 5, 2018 by 1 Lucky Texan

[Zoltan]

Thanks for everyones input.  I will check for a vacum leak.   I do have a question about the timing? Why would it run better in warmer outside air temp than in the cold. Would I be correct to assume that this point more to a sensor problem.

[1 Lucky Texan]

some cars with bad plug wires or coil, or, maybe with oil leaking onto the plug boots, will drive-off moisture when temps increase, reducing misfires. Some folks have even used plant mister bottles undehood at night on their idling car - the mist will show arcing and maybe cause engine stumbling.

 

The other issue could be as I oultined above about the engine temp sensor - if the ECU thinks the car is always at a higher temp, it won't 'choke' by sending more fuel to the injectors when cold.

 

plenty of other things other things; like a gummy deposit in the throttle body or gummy buildup in the IACV or ???? might be different viscosities at higher temps. Metal parts change shape with temp, wires/connectors/ground connections could change a little with temp. I have read of older crank position sensors that failed at high temp......who knows?

Edited October 5, 2018 by 1 Lucky Texan

[Zoltan]

Ok. I check my plug boots for oil, and check throttle body and IACV.  I will report back tommor ow.  Thanks again for your help!  

[Zoltan]

I checked for oil in all 4 spark plug holes. None.  I changed IACV, did not help. I changed throttle postition sensor. Nothing.  I am sure glad pick n pull is a mile from my house. lol  Ok I guess I will order a new front O2 sensor from rock  auto.  I was told this may be the problem. I am in Canada and the shiiping will take 10 days.  I will report back!  Thanks again for everyones help

[montana tom]

Did you change the engine temperature control?  Located on water jacket under intake  manifold on pass side.  (pick and pull)

Knock sensor ?  driver side under intake manifold ?(pick and pull)

Did you check timing ?

Have you done a compression test ?

 Have the valves ever been adjusted ?

[Zoltan]

It was the front 02 sensor!   Thanks for everyone's time and input!