2006 Legacy 2.0R EJ20 Flat spot

[rusty630]

I am after some help from a bright spark out there to resolve a very aggravating problem with my baby....
My NZ new 2006 Legacy 2.0R 5 speed manual wagon (EJ20 - 120,000km) has developed a flat spot during increasing engine revs. The engine accelerates through the rev range as it should until it hits the flat spot and the cars speed remains the same until its out the other side and starts picking up again - often with the same sensation as a turbo kicking in... Most of the time the flat spot sits between 2500rpm and 3000rpm but it has moved around a bit - has been under the 1500rpm mark and also around 4000rpm. It seems to be more noticeable in hotter temperatures and is all but non-existent until the engine is at temperature.

Its been to the dealers a few times to get looked at. They replaced the exhaust oxygen sensors which did nothing. They've also reset and updated the ECU which helped for about 1 hour of driving before it came back. They've looked at the plugs which appear normal. Now the 3 year warranty has run out I cant afford to keep taking it back there to not get it fixed.

Has anyone come across this problem before? And does anyone have a suggestion to a solution?....
I'm dying to get this solved as it is ruining my experience of an otherwise brilliant car!

[green97gt]

bad TPS? ive seen TPS that then you run them thru there sweep with a multimeter attached you can actually see the "dead spot" just a thought. goodluck

[ouch1011]

Forgive my lack of knowledge of other countries models, but in the US the EJ20 is only available with a turbo. Does this model also have a turbo or is it non-turbo?

Do you hear any unusual noises from the engine when this happens? Like a tapping or rattling noise?

[Huffer]

It's a 2.0R, so it's not a WRX (or STi, therefore non-turbo).

What kind of fuel grade are you running, and where are you getting your fuel from? Does the problem only happen under load, or in neutral as well?

Could be a fuel filter, clogging injector etc. Sounds like the dealer isn't diagnosing, but simply replacing parts. The O2 sensors would have been fine till 200,000km.

[rusty630]

Thanks for the replies.
It's a non-turbo. Normally running 98 octane from BP, although sometimes 96.
Problem is only under load. eg from stop in 1st the car pulls as normal until about 2500rpm then acceleration stops and same speed is maintained until about 3000rpm, then a big 'boost hit' and the car pulls away as normal right till redline.
No unusual noises, just that wonderful boxer growl.