bought a hawkeye Sti yesterday from a car salesman, whilst driving home it judders at revs from 3.5k- 4k
as in when you rev it, does revs are holding the car back,.. sometimes if you push it, it can go past it ok, but when it happens it seems to be holding and judders on those revs.

Took it back to the fella and we went to a garage and his OBD reader cannot detect anything.. sensor etc.
no engine light ever came on.
he offered me £100 and I will sort it out myself, which i agreed as I spent the whole day down there sorting out the car.

we kinda narrowed it down to maybe leads (ie breakage etc), spark plugs or fuel pump.

Asked the original owner and spark plugs were changed last year.

Anyone experienced something like this and knows what it can be.

It feels like pressure is feeding to a pipe, but is leaking during the flow and not going through

 

Id start with disconnecting your MAF and test driving it then. If it resolves, you have your answer. Often a MAF problem does not trigger a code. Failing that I would check the condition of your fuel filter. Then look at condition of coil packs, spark plugs. Do it in that order its the most efficient diagnosis path for the problems your describing.

 

Had exactly the same thing on a classic, misfire at same revs and would pull through it and be fine further up the rev range, with no codes or check light.

Lambda sensor was my fault, got a blue print one from a local motor factor for £42

 

The question with these are, when there are no codes to assist you.
How do we get to check lambda sensor stage.. after changes number 5

 

Can only tell you what I did fella.
I went through a process of elimination, I disconnected everything else I could one at a time, and got codes, but it never gave a code for the lambda.

Disconnected lambda and checked with a meter, didnt get a reading, so had to be that

 

thats a clever way.
I will try and give this a go

 

just realised its under the car.. not sure do i have one as it's decatted.
But anyhow, will get the car checked midweek and mention it.. will remove maf sensor and test that as its easier.

 

Ok, it's not the maf sensor,
unplugged it, engine light went on, drove it and problem is still there, so reset the codes.

Now this might not be relevant but, went to put some fuel in and when I tried to restart the car it took about 10 seconds to fire up.

at idle , ie waiting at lights or roundabout, the car feels like it was going to stall, the rev meter drops 1-200 revs as well/

 

Won't be the Lambda - you'd get a CEL.
Unlikely to be the MAF - this is a commonly re-iterated point, but the newages do not suffer in the same way from failing MAF sensors as classics did. Similarly, on a car as new as a Hawkeye I would be exceptionally surprised if a coil pack had failed so early in life.

Most likely candidate if you have no CEL and based on your comments will be either idle control valve, or spark plugs - check what's fitted and the gaps on the plugs.
If the car's unmodified, should be 0.8mm, lightly modified, 0.7mm, heavily modified, 0.6-0.65mm.

If the car's been parked up or not used much for a while, the idle control valve may need "unsticking" - there's a guide on how to do this in this month's total impreza.

Finally - you mentioned it's decatted, but has the car been mapped or is it just running on the standard map?

 

It's fully forged and mapped by Bob,
Funny you should mention this, it hasn't been driven since I last visited which was the 1st, so yeah about 18 days not doing anything.

Can someone upload me a scan of the idle control valve? pretty please!!

 

Just an update, engine light came on and I've taken it to Sheffield Subaru services.
Lots of problems on the engine, running lean, leaking manifold, vacuum issues, this is only by what they can see.

As I've only bought this on Saturday, I will be trying to get my money back.

Worst part is I'm now back to square one and lost Rex who i've owned for over 11 years emotionally :'( which never had a problem.