chrisadsti

Hey Guys, I hope you can help me with this.

2004 2.5L Sti.

Now, I have "the surge". It occured anywhere from 2100 to 3000 rpm, BUT, only at VERY small throttle or on the over-run.
Does not happen at tick over.
( Its actually worst at 2400 rpm when just started from cold ),

I first noticed this 18 months ago, but only when starting from cold, and it didn't seem important, but it has steadily got worse.

I took scooby to a respected Subaru specialist, from whom I originally bought the car, and they said nothing showed up, and suggested changing the air flow meter. That done, the car is smoother overall, but the fault is getting worse. The surging now occurs from 1800 to 3800 revs, still on almost closed throttle only, as before.

Now this seems to me to be a throttle position related fault, can anyone point me in the right direction to cure it ??.

We have several average speed camera set ups round here at 50mph. Now 50mph corresponds to 2400rpm in 5th, and when in traffic you have to sit there with the engine hunting up and down, which is uncomfortable. Using 6th is OK but not for uphill sections.

Please Help !!.

VBR Chris Adams.

ps: the car is a 2004 Forester Sti., now at 54,000 miles. ( 2.5L Turbo, Japan and New Zealand model ).

f4la k

iTrader: (1)

Try resetting the tps, I had a similar problem with my impreza after i had my simtek fitted and i cleaned the tps and reset it, whether the reset works with the simtek or just the oe ecu i dont know, but my car settled down and has been ok ever since.

chrisadsti

Hi There "f41a k",

many thanks for your response, but what is a tps ??.

I am an engineer by the way, I just dont know what a tps is !!.

vbr Chris A.

ScoobyDoo69

iTrader: (17)

Throttle Position Sensor? That's a guess by the way!

nks

iTrader: (6)

TPS=Throttle Position Sensor...Not sure how to reset it though

chrisadsti

Ey Up Guys, so obvious, sorry.

Now we know what it is, how do we go about cleaning and re-setting it. Is there a service bulletin or similar ?.

vbr Chris A.

ps: I see peeps referring to an "MAF". I know what an Air Flow Meter is, but what is an MAF ??. Please don't say it is a Meter for Air Flow !!.

bmfcrash

iTrader: (14)

Ok, I wont say it is the Mass Air Flow sensor then

joz8968

iTrader: (13)

^^^

Scooby Dan

Does the car have an induction kit fitted ?
I had a similar problem on my STI and it was caused by a cold air feed to the induction kit which was causing turbulance around the maf.

chrisadsti

No Scooby Dan, the car is standard, Sti standard anyway.

Any ideas as how to "reset" the tps ??.

vbr Chris A.

Minjeeta

swap it with one of the tumble generator valve position sensors.....or is it AVCS actuators on your engine?

Anyway, what kind of surge are you on about? Boost Surge? Fuel Surge? Bladder Surge? Surge for the wifes tats?

chrisadsti

Ey Up Minjeeta,

thanks for that sensible advice. As I pass the Fire-station each morning and there are two fire-engines, I suppose it could be B ladder Surge !!.

Actually this is a genuine problem, it feels like you are gently squeezing and releasing the throttle pedal but you are holding it still.

vbr Chris A.

Saint AAI

How many miles has the car done and have you ever changed the Lambda sensor?

chrisadsti

Ey Up Saint,

I really do appreciate you guys trying to help me out. The Subaru agent is talking about swapping parts, which is OK until he says the tps is £450, and the O2 sensor £260, plus labour !!??.

The car has done 54,000 miles, one owner, full Subaru service history, and no I haven't changed the lambda sensor. Have you done this ?. Did it cure the problem ?. How much does one cost ?.

I don't mind spending money on the beastie, but the thought of another £1000 parts and still not cured is painful.

VBR Chris A.

joz8968

iTrader: (13)

I can't believe the TPS is THAT much!!!!!!

Robin Hood had nothing on Subaru main dealers.

markjmd

iTrader: (11)

All things considered, wouldn't the best way forward for the OP be to get a hired hand in suitably equipped with a laptop and logging software, and take the car out for a drive until the symptoms show up again? Seems like it would make better sense than the dealer's scatter-gun parts-swapping approach.

chrisadsti

Hey mark,

I'm all for a more diagnostic approach, but do you know anybody who could do this in my area, Sth Yorks / Nth Notts ??.

vbr Chris A.

markjmd

iTrader: (11)

A few names that come to mind:
Duncan at www.racedynamix.com
Zen Performance
Zak at www.mocomracing.com

These guys specialize in re-mapping, but I'd guess the same software will work just as well for diagnostics. That's a bit of a 2-sided coin though, as the better mappers tend to be booked weeks in advance a lot of the time.

chrisadsti

I have been contacted privately by a guy not far from here, and he says he can help.
I hope it works.

Thanks for the links Markjmd, I am nearer to Zen than the others. I will ring them tomorrow as I am down in Wellingborough next Sunday !!.

vbr Chris A.

Saint AAI

Is the problem worse when the car is cold aswell? Lambda sensor is the O2 sensor, so I'm guessing it's £260 from your previous post. That seems far to expensive to me though. Your mileage ties in with it possibly being the lambda/O2 sensor too. Not saying it is that though, just my guess. Narrowband Lambda sensors give out a voltage somewhere in the range of 0-1V, if the voltage is above around 0.5V then the ECU sees the mixture as rich, if below then lean. From what I understand, the ECU only takes notice of this reading under light load/part throttle conditions where it is safe for the engine to run a stoichiometric mixture. If the mixture goes rich, then the ECU drops the fuel until it sees the voltage drop below around the 0.5V, then it will raise it again until it goes above. If the sensor is on it's way out or not warm enough it may take a while to react so the ECU will keep dropping the fuel for longer until it sees the voltage it wants and vice versa. When the engine is under load, the ECU goes "Open loop" and ignores this sensor altogether as it becomes pretty useless at this point, it will be reading rich all the time. You could try unplugging the lambda sensor, with the ignition off, and then taking the car out for a small test drive. It will probably turn on your check engine light, but if the problem goes away it may prove it is the sensor at fault.

As I have said before, this is just my understanding of things and so may not be completly accurate, hopefully someone with more experience can correct me if any of it is wrong.

dynamix

iTrader: (3)

Easy test on the O2 sensor is to unplug it (top plug near drivers side strut top).

This will obviously bring on a CEL but it will stop the O2 sensor interfering with the fueling and essentially take it out of closed loop fueling.

If it does cure it - then get a new O2 sensor.

CEL can be cleared by turning the igntion on and off five times.

chrisadsti

Hey Guys,

Many thanks for the help. Took the car to Scooby Newbie yesterday, isolated a problem with the tps, working on that at the moment, but will try the lambda probe test today cos your explanations fit the bill.

Again, help much appreciated, its a brilliant car !!.

vbr Chris A.

scoobynewbie72

iTrader: (1)

02 was working fine, nice voltage and responded quickly

chrisadsti

rite toe