Hesitation on WOT (V70 2.0 T5 AWD 1997) Topic is solved

[misha]

We are back on the beginning.
Like abscate pointed out...it doesn't necessarilly mean that Maf is bad.Being a Bosch unit and symptoms doesn't match with a bad Maf...it could be just a vacuum leak or exhaust leak before o2 sensor.

That said...Flexi pipe between exhaust manifold and cat can also disturb fuel trims...so as exhaust manifold gasket.If they are cracked,they sucks in "false" air,which wasn't metered by Maf,but o2 sensed it.Intake manifold gasket too.

Maf and o2 works as a team...volume of entered air measured by Maf MUST correspond with volume sensed by front o2.
If there isn't a match,ecu isn't happy and it tries to adjust the fuel trims with the best way it can to keep the engine running at it's best.Sometimes it runs rich,sometimes it runs lean.

With your symptoms...it must running lean.
I would also check ALL hoses connected to a turbo...sounds like there is no enough boost.
Injector's o-rings could also be a culprit....everything is possible.

ALL vacuum lines MUST be checked,exhaust system before front 02,intake,codes read...etc...in order to proceed further.

It could be something simple since check engine light isn't ON.

Almost forgot...
Since we determined that you have M4.4 ecu....if you can find a VAG-COM KKL serial cable,i can send you VOL-FCR via e-mail.
Note that it's version 1.3.0.6 and it's for serial cable(db9) which requires an old laptop or desktop.
There are also adapters which can convert serial cable to USB but i don't know anything about COM1 port settings in this purpose.

[Fiodor]

Pcv system vacuum lines Where are these ?
Fuel tank vent lines What are these ?
Vacuum tree vacuum ports CHECK
Sas system(if equipped) vacuum lines What is the SAS system ?
Brake booster vacuum lines Where are these ?
Fpr vacuum line Where does this one hide ?
Fuel tank cap must be OE and tight untill it clicks CHECK
Air filter housing vacuum lines I don't think I have any
Right side of intake manifold between ps pump and intake manifold...vacuum elbow CHECK

Thanks again for helping me out, I used to have a 740 which was much easier to work on... But I love this one and it drives me mad to have small issues like that.

Edit: I have a VAG COM KKL cable with USB, I think it's supposed to work if I reduce the data transfer speed

[misha]

Pm me your e-mail and i'll send you the software.

PCV is a little different on turbo cars....i would wait for instructions from owners with turbo cars.

Fuel tank vent lines...1st check the purge valve on the fan shroud.It must be closed when disconnected and ecu opens it when it's needed.

SAS...secodary air injection system

Brake booster have only ONE vacuum line and it goes from intake manifold too a brake booster check valve(white valve)

FPR vacuum line...M4.4 cars have it at the back of the car near fuel filter or at front at steering rack area...

Air filter vacuum lines....Turbo cars don't have hot air flap at air housing as far as i remember....so scratch this

Right side of intake manifold vacuum line....check the other side connection if that one is ok.

[Fiodor]

Thanks !
I'll post an update once I get to plug my car to my computer !

[Fiodor]

I received my feeler gauge today, my spark plugs were gapped at 0.035 at least!
I've regapped them to 0.028 but haven't had the opportunity to take the car for a test drive yet.

[Fiodor]

Some news, took the car for a drive this morning and it was working perfectly, no stutter at all, perfect idle, I was so happy.
Then I returned home and picked up my father so he could see for himself. Unfortunately the symptoms came back when he was driving.
I've re-checked the spark plugs and nothing's wrong with them.

When I started the car with the plug cover off the first wire from the right made a loud POP 5 seconds after starting the engine.
What could be causing this ?

Edit: I scanned the car with VOL-FCR and I don't have any codes.

[Fiodor]

Any ideas ?.

[misha]

...When I started the car with the plug cover off the first wire from the right made a loud POP 5 seconds after starting the engine.
What could be causing this ?

Edit: I scanned the car with VOL-FCR and I don't have any codes.

It seems that re-seating spark plugs wires and re-gapping spark plugs made a difference...for a short while.
It could be bad spark plugs(Denso) or related wire.Check if wires are fully seated if they are Bougicord.That POP would be a heavy misfire.
Ecu can't set dtc since it happens intermittently and only at wot.
That said....as soon as you back from high rpm,engine works good and ecu don't see a problem to set dtc.
Even if it sets it for a moment...it clears the fault and there is no code stored.
In this case..live data at WOT must be retrieved.
I would carefully examine wires and put in a cheap copper Bosch or NGK spark plugs,gap them correctly and see if problem go away.
In the meantime...you can re-check timing marks.

[Fiodor]

How could I examine the wires ?
Like with an Ohmmeter ?
They are original Bougicords

[misha]

Check if that wire which maked a pop is fully seated on the little "hat" on the spark plug untill it clicks.
If needed you can squeeze the wire's opening with a long pliers if it doesn't fit tight.
They can be checked with multimeter,but i never did that...and don't know what resistance they should be.