Any ideas what this is?
 

Hi all, I have an 01 Bug WRX - on a daily basis from about 2700 to 3700 it has a stutter or jerky acceleration...
Some days its just noticeable, others its very jerky.
It doesn't seem to be better or worse when the engine is hot or cold.
I have changed the plugs and the cam position sensor.

I do get a CEL showing mixture lean bank 01. This has come on - usually when just cruising - for months now, out with the judder which started about a month age the car ran perfectly. Even with the CEL error.

I cant tell if the boost is being held back by the solenoid as it only happens as it comes on to boost.

I am running a TD05, pinks, STi inter-cooler, 255 pump,Perrin intake, Prodrive sportcat.

Any thoughts would be appreciated.

Cheers.

MAF .............. clean or replace

Thanks for that Don.... I checked it was 'working' with my Torque app and it is reading the intake air mass, but I guess the ECU analyses that way faster than I can (or the Torque app can) see.
I will give it a clean out tonight.

Thanks again.

Might be a daft question, but has it been remapped for the mods?

Fuel/boost cut?

Hi Ian, not a daft question, I should have said.
It was mapped by one of the best Andy Forrest.

So, any thoughts as to what would cause it?

It feels quite a sharp jolt, So I had wondered if it was a coil pack, but wouldnt have thought one pack failing would be so 'violent'.

Definitely sounds like fuel/ignition/boost cut.

Basically if the ecu senses det/overboost etc it will cut ign, fuel or boost (not sure which on a scooby) to protect the engine.

Which considering you are getting a lean running CEL code the ecu is saving your engine from explosion by the sounds of it

That all make sense Glanza, I wonder if its injectors then, they may well have been getting steadily worse; but why is it during the boost transition period?

Thats what I couldnt tie in.

Thanks for your thoughts by the way :thumb:

I should have said that I cleared the CEL's yesterday and it shuddered a couple of times and no CEL came on. Just to throw something else into the pot!!

Cleaned up the maf so I will see if there's any improvement

Is it only under hard boost? If its under hard boost could be the boost control solenoid.
But if your saying it has a lean mixture I'd give the Lambda sensor a go. Im sure if you unplug it and run the car it may throw a CEL on but it may correct the issue as it will run off the base value given by the map. See if that helps, if it does look at getting a new lambda sensor.

You have an air leak. Thats why its showing as lean. Check the Y pipe under the intercooler.