+25 STFT at idle... Ideas?

[kevstewart]

Hi guys, installed new turbo and downpipe along with EGR block off plate at the weekend and since then I've had high STFT(short term fuel trim)at idle... I've removed intake/turboinletpipe and checked all the simple things without success.
Any ideas?
The V band clamp at turbo/downpipe was a little awkward to sit right, could this cause my troubles?

A CEL popped up for too lean at idle as I've got unmetered air in the system - where do I go from here?

Many thanks, Kev

[SarcasticOne]

Changed size of MAF?
Boost leak?

Sent from my Galaxy Nexus using Tapatalk 2

[kevstewart]

Maf and SRI/TIP are all existing stuff. I'll do a boost leak test tomorrow to see if anything pops up. Could exhaust leak cause this?

[Axspeed6]

if its a big gap then it might cause you o2 sensors to read incorrectly (on the lean side) but the other metering sensors + the ecu's own check algorithms that deal with faulty o2 sensors etc and tell you that they are bad but v-band clamps are pretty damn good at sealing things that's why they're hard to get on, is it a cat-less downpipe???

[RedDjinn]

Sounds like something i had, ended up being a connection on 1st sensor on DP. Check the connection of all wires in the plug

[Axspeed6]

always good to get some electrical contact cleaner and give your wiring plugs a clean before installing

[Bakis]

Do you mean LTFT? On my dashhawk the STFT is NA but LTFT gets a reading :S...

My LTFT varies from 10.7% to 18.5% :S something is leaking in the pipes and can't find it for the lift of me might be exhaust or turbo but atm im stumped... Under load it reduces to 4.7% and 3.5% so i got no idea what the hell is happening.

[kevstewart]

Thanks for the tips guys... I'll check out sensor connections and give them a quick clean up too.
Before install my fuel trims were really good as maf calibrated via Versatune... + or - 3 at worst.
LTFT remains normal, STFT at idle is only problem.

---------- Post added at 11:38 AM ---------- Previous post was at 11:37 AM ----------

also downpipe has 200cell sorts cat welded in but after both sensors and the CEL that would pop up has been deleted via Versatune also...

[kevstewart]

Things got a bit more interesting today:


Set off on my shopping trip today - fault still on the car, 30+ miles journey 60-70 mph but a couple sets of traffic lights, went to first shop, fault still there, cruised along 30-40 mph to another shop and as parking up the fault cleared!!!
STFT returned to normal and started trying to bring down my LTFT... Idle Air fuel ratio perfect(under fault conditions it sits around 16.1 and triggers fault code for lean idle)


Off I went to two more sets of shops and filled up with fuel - fault gone..... However on my journey home I got about 20 miles at 60-70mph and the fault came back - STFT returned to +25 at idle and also at other low maf ranges at was increasing my LTFT's...


Returned to my town, picked up a chinese, fault still there... Car off, car on, fault still there, I set off again, 20mph, turned down my street(this is a matter of ten seconds)and fault cleared! Very strange!
Car now parked up at home with no troubles / untill I go for another drive up to 70mph I'm guessing.


Bit more information for you guys anyway, intermittent fault which seems to clear doing low rev/low speed driving and appear after driving 70mph for a while...


02 sensor?
Perhaps a slight exhaust leak which gets blown when driving at speed but clogs up at low speeds?


Bit of a long post but more info the better - thoughts/opinions welcome

[kevstewart]

Looks like purge solenoid valve is the culprit... Removed and it's allowing airflow.
This part:
I'll get a replacement ordered tomorrow and hopefully problem fixed!

[Bakis]

Where is this in our engine bay?

[kevstewart]

It's here:


Very easy to replace and a cheap part too

[Bakis]

@kevstewart can't see the pic sorry mate

[kevstewart]

It's between intercooler and battery, you'll see a check valve then the purge solenoid with a plug on it next to each other. Don't need to remove anything, in a very good position for replacing.

I was hearing a hissing from check valve - the solenoid stuck open so allowing air through and into the engine causing it to run lean.

Seems a 'common' fault on MSF

[Bakis]

Thanks ill look into it on mine

[kevstewart]

Mazda part no. L3K9-18-740B (Bosch part)
Dorman part no. 911-702 (much cheaper)

If you hear the check valve hissing it may be your problem too, normal idle it should make zero noise and purge valve in closed position.

I actually dropped my solenoid and it closed up - it must of been sticking causing my problems to go away then return randomly.

[Bakis]

just had a check on mine and no noises at idle and have it a tap to see if it was sticking and nothing , my search continues lol

[MattMPS3]

An easy way to check is to remove the solenoid from the engine bay (all of 5 mins), then apply 12v to the terminals of the connector, when there is current to the solenoid you should hear it click open, which should allow you to blow through it, when you turn the current off it will close and you shouldn't be able to blow through it.

[kevstewart]

New part installed, problem fixed... Hopefully helps out someone with similar troubles