o2 sensor

[willz52]

I know there is a lot about these on the forum have read a couple. A lot of people seem to also point there problem to another factor but im just checking if this could be it...

From cold start up it will sometimes idle high (1,500 as it should while warming) but then fall down to normal idle speed (800) which i can tell is not right because it hasn't fully warmed up yet and needs it higher revs to warm correctly before idling at that speed. Once it is getting warmed up then it is sweet as. no flucturations once warm.

Also surges when you are light on the throttle but when you give it some boost it is perfectly smooth.

Haven't tested for voltage on the o2 sensor as of yet.

Car is v3 1997 sti, rebuild engine, cleaned IACV, changed AFM, surging was happening before the rebuild so it is nothing to do with that. Only thing that hasn't been changed that could do the surging is my o2 sensor and i havent changed coil leads or the coil pack but that itself looks fine.

Guessing its o2 but anyone got other suggestions?

[funkytown]

TPS..

[gazzy2000]

Yip sounds like an o2 issue, a Bosch 3 wire universal is what you are after.

You will pay btwn $130 -$170 for one of these compaired to $300 + for OEM subaru (of which is Bosch any ways)

i had really bad surging on my 97 STI and it fixed it. I have also used one on my 2001 GTB with no probs.

You must reset ECU after you change it too,

EDIT: also for surging issues.. make sure you have the same series tyres alround and pressures are the same, have seen wrong diameter tyres i.e. 45 series on front and 50 series on the back cause surging as the center diff slightly binds up with different rotational speeds.

[willz52]

Cheers, so any old Bosch o2 sensor thats 3 wire will do the trick? Never had to buy one before. And just from the usual stores??

[Guest keltik]

Umm....the 02 sensor isnt used during warm up is it?

Im with Funky. Smells of a Throttle position sensor to me.

[gazzy2000]

 willz52 said:

Cheers, so any old Bosch o2 sensor thats 3 wire will do the trick? Never had to buy one before. And just from the usual stores??

Just go to a reputable auto electrician and tell them the car you have and the year etc... quote the "bosch 3 wire universal" to them and they should be able to hook you up.

[willz52]

so tossing up between o2 and TPS. No codes being thrown by ECU....

[gazzy2000]

 keltik said:

Umm....the 02 sensor isnt used during warm up is it?

Im with Funky. Smells of a Throttle position sensor to me.

Surges under light throttle but boosts otherwise fine + idle surging when cold....

Exactly what i had on my 97 STI, o2 fixed the works, incl better fuel economy. I did the works finding/diagnosing the problem.

[gazzy2000]

 willz52 said:

so tossing up between o2 and TPS. No codes being thrown by ECU....

Yip exactly what mine did too.... no CELs

Be keen to hear how you get on with it!

[willz52]

sweet as ill give it a shot.

[gazzy2000]

Hey, it would be a good idea to reset your ECU (if you havnt already) after cleaning AFMs or IACVs etc etc, so the ECU can "unlearn" the false readings from faulty sensors.

This will ensure you havnt fixed the problem already, if you know what i mean.

I always reset the ECU after changing or cleaning any sensors to let it "re-learn" sensor inputs

Let us know, cheers

[funkytown]

 gazzy2000']

[quote name='keltik said:

Umm....the 02 sensor isnt used during warm up is it?

Im with Funky. Smells of a Throttle position sensor to me.

/quote]

Surges under light throttle but boosts otherwise fine + idle surging when cold....

Exactly what i had on my 97 STI, o2 fixed the works, incl better fuel economy. I did the works finding/diagnosing the problem.

yer and this is what i had one mine as well... was the TPS.. likely to be one or both of them...

espec the surging on light throttle..drove me mental

[willz52]

hmmm. anyone got a half good one of either that i could test??

[funkytown]

 willz52 said:

hmmm. anyone got a half good one of either that i could test??

2nd hand TPS's to test are cheap as ****.. get one from a BD or BG legacy - they are all the same.

They requie careful calibrating tho on a stock ecu.

[Guest keltik]

Simple fix. Unplug one and see when the problem goes away. Im assuming the EJ20 runs without a TPS....

All i know for sure is that the 02 sensor isnt used on warmup at all - so that wont be the cause of your idle issue

[funkytown]

 keltik said:

Simple fix. Unplug one and see when the problem goes away. Im assuming the EJ20 runs without a TPS....

All i know for sure is that the 02 sensor isnt used on warmup at all - so that wont be the cause of your idle issue

and a TPS will mine used to stall and the voltage was all over the shop - i.e TPS totally shagged

[gazzy2000]

Yea, it can be a process of elimination.

If your car has over 100K on it, i wud do an o2 regardless.

You just saved yourself $100-180 by learning about the 3 wire universal ;D

Plus you are doing it yourself, so you have saved heaps of $$$ right there.

Thats my fiddy

[driftrex]

tps is cheaper, so obviously would make sense to change that first, expect to pay around $20 2nd hand.

could be 02, but i have known a few people to always think thats the cause if every problem they have and turns out its not after going and buying one.

and yea 3 wire universal was about $180 retail last time i got one (however i dont pay anywhere near that ;D)

[Guest]

 driftrex said:

and yea 3 wire universal was about $180 retail last time i got one (however i dont pay anywhere near that ;D)

I made the mistake of getting Subaru to replace one of mine... fark it was expensive! Doh!

[gazzy2000]

bosch 3 wire universal o2 Sensor

[willz52]

cheers for that picture!

[gazzy2000]

 willz52 said:

cheers for that picture!

No worries, that should be the one. Let me know if you have any worries coz i can speak to the auto electrician i got it off (my old boss)

cheers

[willz52]

just put in new o2 sensor, old one looked f***ed. went for a spin and seems alot better in regards to surging. I'll know in the morning from cold start but think its solved most of my issues! thanks.

[gazzy2000]

 willz52 said:

just put in new o2 sensor, old one looked f***ed. went for a spin and seems alot better in regards to surging. I'll know in the morning from cold start but think its solved most of my issues! thanks.

Nice one! Did you remember to reset the ECU?

[willz52]

yea sure did. all seems good. will let u know how it is in the morning.