2000 STI Running rough between 2500 & 3000rpm
 

PLEASE GO TO POST 9

Its been doing this for a few months now. When driving easy there is a slight hesitation as you go up the revs. This gets worse the quicker you accelerate.

Once in boost it flys but getting there is orrible. Feels like its running weak.
I do not want to start buying sensors blindfold.

So I'll ask the experts first. Any clues? It is a standard import 60K miles. I run it on Tescos super-dooper fuel. It has a HKS filter in the box.

Perhaps its expecting better fuel.. the import requiring 100RON?
What about a remap for Uk gas and use Optimax? Just a thought....

Usual answers
 

The usual replies you will get will be:
When were your spark plugs last changed?
""""""""""""""""""""""coil packs"""""""""""""""""""""?
And as mentioned before you need to put in a bottle of Octane booster in your tank every fill up to obtain the 100 ron required.
Also are you getting any CEL light coming on the dash?
Try the above then come back to us;)
I would put money on coil packs at 60,000 miles if they are the original ones.

Kev.

Thanks. I'm using tescos 99 ron or optimax. I've dropped in some octane boost and it did go better but it still had the flat spot. the filler flap has a 98 ron sticker and it was imported from new and I think it has been converted professionally.

I changed the plugs. No improvement. I've not had the CEL light up. I tried unplugging the o2 sensor and the light came on then. So the bulb works!

I'm no expert but it dosen't seem like a misfire. It just jerks a bit, hardly noticable accelerating in 4th or 5th but in 2nd or third when you are giving it a bit. Quite bad like somethings cutting out or is slow to react, or just hardly any fuel at that point. Does this make any sense?

Forget the comment about coil packs, they weren't fitted after 1996.

It sounds like a fuel cut, which suggests that it has an electronic fault or overboost.

It'll help to do an ECU check, which is quite simple assuming you are not afraid of cars. Advise us and I or someone'll talk you through it.

If you want to call me at the office late morning Tuesday.

David APi Engines / APi Impreza
www.apiengines.com
01926 614333

Thanks very much. I'll give you a call.

Does it get worse the warmer the car gets?

Try unplugging the o2 sensor and driving it like it. I had a very similar thing and it was a dead o2 sensor. Mine was quite severe though and it got bad real quick. When the car was nice and warm it just didn't want to rev, if you kept your foot planted the power would eventually come in.

It is not so noticable when cold, but then I take it easy until it has warmed up. What's really weid is sometimes it is a lot better than others. I thought at first that it was to do with the amount of fuel in the tank it seemed to be worse when it was low. now I don't think so, it never goes away its just better some days than others.

If it's a fuel cut (like David @api says) it'll be a harsh cut out during acceleration, ie flooring it then BANG engine stops for a split second.

From your description it doesn't sound like that to me?

It's worth pulling the plug out on the o2 sensor and seeing if it's any different, takes 2 secs and will elliminate this if it doesn't change anyway.

As I said mine was bogging below when the boost came in, slightly when I got it and then got gradually worse. I unplugged the o2 sensor and it revved ok. Got a new sensor and it's sweet now.

Think mine is starting to do the same.Bloody annoying!If i get to the bottom of it before you i'll let you know Rod.
All the best
Dan

R us still on the original maf? I had a maf go on my MY00 after <3yrs and 20k miles.

Similar sounding symptoms, the 2000 yr maf's werent very robust.

thanks for all the help fellas Ill try unplugging the o2 sensor and see what happens. I will let you know how I get on.

Solution Found
 

I would like to let you all know the problem was caused by the MAF sensor unit. I bought one from David at API Engines Mail Order. Arrived the next day!. Reset the ECU and I'm driving a differant car. It was quick before but now its right RAPIDDDDDDDDD..... It runs smoothly up the revs no jerks or hesitation at all. Thanks for your help people! :luxhello:

Good Luck, Thanks for the comments about API:thumb:

Most of all thanks for your business.

David APi Impreza / APi Engines
www.apiengines.com