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TDI Boosting on idle ??

Cupra_Red

Cupra_Red

Jan 13, 2010
440
0
UK
06 plate FR pd130

Problem is : whilst on idle it will all of a sudden start to create 0.5 bar of boost with out reving it ?? then it will idle as it should and then go back to create boost and this will just keep happening

Also when logging the car, ecu is requesting 1.3 bar (stock) and the car is spiking to 1.7 bar and holding 1.5, then it peaks back up to 1.7 after holding 1.5 for a few seconds

The car is not mapped as the requested boost is 1.3 bar and thats stonk, also the car does not go into limp mode.

the car pulls hard and no flat spots but it is not good to boost that much with no additional fueling.

im thinking maybe the vacuum control box has a internal leak? not being able to send enough vacuum or somthing?

actuator is nice and free and i dont think its the vnt mech as the accuator moves to freely for sticky vanes

your thoughts please
 
Yes and no.

It requests a certain boost so control valve opens to pull on the actuator. It doesn't move as much as it was expecting (due to broken pipe) so it opens the valve further to open the actuator which then opens it too much so it then drops the ammount of vaccum but then the turbo actuator isn't open enough (again due to split pipe) so the process repeats. That's how I think it works which could explain the fluctuating boost.

Phil
 
Tried a new vacuum box and still the same problem.

Noticed ye car has no cat and no silencer on exhaust and it's a standard map? Would this cause problems to the car creating boost at idle and then dropping back to normal idle and so on?

Audi tech has had it for the morning and my mate works in skoda and both of them don't know what to do next ?

Ain't looked for split pipe yet as they seem to think that it will not cause it to boost at idle and to have a massive spike when under load
 
Sounds like the Mass Air Flow meter is playing up.. one of my mates put a resistor in it (for some unknown reason) but it basically tricked the car into thinking it was running full air and it gave full boost even sat still and revving it up. Obviously you haven't removed the MAF but it sounds like your having the same symptoms.. try unplugging it and see if it makes and difference :)

Paulie..
 
Unplugged the maf and it drives the same, the maf is pulling the correct air through aswell checked it on vcd, obviously when it randomly starts boosting it pulls more air and then it's out of the specified range but when it drops back to normal idle it's in the range
 
When it's producing boost at idle, is the VNT mechanism moving? If so, disconnect the vacuum pipe to it and see if there's random vacuum being produced by the control.
 
Viking said:
When it's producing boost at idle, is the VNT mechanism moving? If so, disconnect the vacuum pipe to it and see if there's random vacuum being produced by the control.
Click to expand...

yep the vnt moves, take vacuum pipe off it idles ok with no boost, i have changed the vacuum control box with a new one and no diff
 
Last edited:
T10HJP said:
Sounds like the Mass Air Flow meter is playing up.. one of my mates put a resistor in it (for some unknown reason) but it basically tricked the car into thinking it was running full air and it gave full boost even sat still and revving it up. Obviously you haven't removed the MAF but it sounds like your having the same symptoms.. try unplugging it and see if it makes and difference :)

Paulie..
Click to expand...

Something wrong there, the MAF is basically an injection quantity limiter. There are 3 main limiters on injection quantity, accelerator pedal, ECU torque limited and MAF limiter. The ECU uses the lowest of the 3 at any one point. So even if a MAF is faulty or a resistor used, if the throttle wasn't touched it shouldn't boost or rev high or anything.

A stock map shouldn't requests boost when the vehicle is stationary. The only time this should happen is when it has been tuned for launch control.

Sounds like something is energising the vacuum control box for what ever reason if you've substituted if for a known good one.

Have you monitored any of the sensors at idle if you revs are fluctuating?

Also when logging the car, ecu is requesting 1.3 bar (stock) and the car is spiking to 1.7 bar and holding 1.5, then it peaks back up to 1.7 after holding 1.5 for a few seconds

The car is not mapped as the requested boost is 1.3 bar and thats stonk, also the car does not go into limp mode.

the car pulls hard and no flat spots but it is not good to boost that much with no additional fueling.
Click to expand...

correct, based on the BLT stock map, the 130PD should request max 2350MBar (Absolute) between 2500-3750 rpm, but it can be mapped (lightly i.e an eco map etc )with stock boost as the TDI PD in particular are "rich in air" so injection quantites can be raised without needing to modify boost. On another note, 1.7 (~2.7Bar Absolute) of boost on that turbo is not good regardless of additional fueling.
 
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Ye all sensors are all in specified range on idle, until it starts making boost at idle rev's then all of the specified ranges are out- due to the spoiling of turbo pulling more air through.

The map is 200% stock it's been sent off to two well known tuners to confirm it's stock.
 
I monitored my requested boost today with the car stationary, at idle I had basically no requested boost over ATM and had to rev right up to get 0.3Bar "actual" .
 
The cat removed will affect back pressure yes, but that's not what controls the boost, the ecu (N75 pilot map and PID controller), vacuum box, vanes and actuator control the boost. This is especially true at idle You've proved where the problem is when you disconnected the vacuum box and it when back to normal.
 
I bought a new vacuum box and same
Effect still boosts

Car will idle tidy then it will RANDOMLY creat boost then stop then boost again.

With the vacuum pipe off the actuator it does not boost at idle.
But a new box did nOt solve it
 
Cupra_Red said:
I bought a new vacuum box and same
Effect still boosts

Car will idle tidy then it will RANDOMLY creat boost then stop then boost again.

With the vacuum pipe off the actuator it does not boost at idle.
But a new box did nOt solve it
Click to expand...

Yip I understand that, and my concern is why the Vacuum box is activating, because it shouldn't.

I wonder if you don't have some Dodgy wiring to the vacuum box or something's up with the ECU.
 
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Car seems to be getting louder in a tractor sounding way the more I drive, no smoke though and it boosts like mad as you'd expect at 1.7 bar lol

Coming to te end with this car now!
 
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