Hard acceleration stutter
 

Hi,

First time on here so firstly hello!
Any feedback to the following would be much appreciated.

I have a 98 sti version 4 that was working fine up until last week (I have owned it for about a month).
When I accelerate hard and it reaches just under 3000 revs then is starts to stutter.
The stutter frequency is not as spaced out as that in the following youtube vid but this is the closest thing i can find to show you the sort of thing I am on about.

http://www.youtube.com/watch?v=c3wM3VvgqVE

The stutter itself is very brief but its frequency is about about twice per second (roughly).

I have been having a read through the other similar posts, and the main things that have come up so far are:

MAF sensor
Lamba sensor
Spark plugs
Coil pack
Cylinder compression - hopefully not!

I am not sure if it is relevant but the car has (since for past 6months) had varying idling speed (between 700 - 1300). It was more common when cold but is now more intermittent.

Right, enough waffle from me.

Like I say, any advice is very much appreciated!

Thanks,
Ben

I have something similar at the moment though it only stutters at max boost. All signs point to spark plugs which I've got on order.

I'd be looking for an air leak or split vac pipe first .

I had the same on my95 wrx every time i went over 0.8ish bar it was blowing the spark out then did a plug change and gapped them to size and job done, now iam at 1bar with no probs at all.

thanks fellas:
- we had a quick look over the obvious hoses/pipes last night and all seem fine but maybe some could do with an extra clip.
- spark plugs are getting ordered asap so will try that also

thanks again!

sti345 - thanks to you also - will get the spark plugs sorted - see if that makes a difference.

cheers

any mods? has it been mapped for them?

the car came with limited history as it was only imported in 2009 so am not fully aware of the mods list but as far as i know only a japspeed exhaust.

someone i know had it for a few months prior to me and all had been ok - would mods not immediately start causing issues?

thanks

decat without map, temps are dropping and thats when overboost happens. I wojuldn;t be surprised if it was the MAF considering the iratic idle as well, short version is get it looked at by someone who knpows what there doing and they can find the fault.

appreciate that Tidgy, thanks!

Sounds like MAF to me too, might also be worth reading for any on board fault codes.

what sort of price is it usally to get these readings?
would i need a subaru specialist, or can it be done on any garage code reader computer type thingy?

cheers

Until you can rule out the maf, keep the car off boost.

Faulty Mafs are potential engine killers!

In fact, it's a good idea to keep the car off boost until the cause of any such behaviour can be identified!

Ns04

ok, cool, thanks.

have been reading up about using an electrical parts cleaner to wash any dirt build up on the sensor. is it just a case of spraying it, or is it worth giving it a light wipe with something like a cotton bud?
if the sensor is not dirty but just knackered, how would i determine this?

also, what is the liklihood of the fuel filter contributing to issues of this type?

thanks

What boost is your car making when it stutters/cuts?
Do not run the car into this condition as it could destroy the engine.
Look at the boost control pipework for a leak.
Has anything been changed?

Not sure what boost it is running, no gauge. Are u saying don't run the car at all, or just don't push it up to the revs where the issue becomes apparent? Thanks

Keep the car off boost, i.e. just nurse it to a place where it can be diagnosed properly. Most specialists will put a select monitor on the car and look for sensor error codes FOC.

Getting this sorted now could save you thousands!!

Revs has got little to do with it. More to do with throttle position and boost you apply or put it another way, the load on the engine. Do not give it any hard time and get the issues sorted sooner rather than later.

Hi,

Got some new plugs (NGK PFR 7B) and that did the trick.

The idling speed still varies but intermittently. Most frequently when cold.
Once warm it seems to be ok.
Most people are saying that the MAF would not throw an error if faulty so I did try my mate's MAF in my car and idling seemed better (but then that may have been coincidence due to intermittent nature of issue). Obviously the hard acceleartion issue issue was still there when i tried this swap (prior to plugs being changed).
Anyone got any idea of how to ensure that the maf is ok? Don't want to damage the engine if it is not working as it should.

Thanks for everyones comments so far, very helpful!

Cheers

Mate, you REALLY NEED to get this to a specialist to diagnose properly.

You don't want to be taking stabs in the dark and testing your theories by subjecting the car to the conditions where the stutter occurs if something is wrong, as if it's a duff sensor, it could kill your engine! Then you're looking at a 3k bill for a rebuild!

It is literally a 2 min job for a specialist to plug in the select monitor, even if the maf hasnt thrown a CEL the voltage range parameter readings will tell the specialist if it's on the way out! People have had engine failure attributed to a MAF on the classics without so much as a hint of a CEL.

If the car isn't idling properly, something is up. Simple as!

Ns04