got a st170 keeps on juddering in between 1000rpm to 2200rpm sometimes with a misfire and now and again it won't rev over 4500rpm like its restricted have already change the fuel filter,plugs,air flow metre,crank sensor,fuel rail and the coil pack but still have the same problem any help would be appreciated!

 

Does it sound muffled or is the cat rattling ?
tabetha

 

no the cat isn't rattlin it sounds like its choked or something but it runs fine once its over 2200 rpm

 

Are you using BOSCH plugs ?
tabetha

 

ive had this problem in the past, if you look at the plugs and you could see like a little line on the ceramic part going top to bottom then its the plugs and the leads will need to be changed at the same time.

 

no not using bosch plugs i'm sure its nrg platinums that got put in it maybe 4 months ago and the problem has just started 2 weeks ago! i'll take them out and ckeck them cheers guys

 

the ngk's are shit mate

 

If it feels like its choked up when trying to move off from stopped then I would have a look at the O2 sensor, when they get old and covered in carbon deposits they tend to think that the engine is running rich. As a result, you'll be getting less fuel into the engine and you'll be experiencing a lean misfire (feels like the fuel isn't getting through, which is what is happening).

It helps if the car has a post cat lambda as well, because when this was happening on a new clio I looked at (emissions light was on but EML wasn't) the lambda looked like it was working fine, but the post cat was indicating that the engine was running far too lean. New lambda fixed the problem instantly.

ECU wasn't picking up a fault because it beleived the Lambda was working right. A cheap code reader will show this and will save a lot of money in the long run (MAFs, Plugs and coil packs cost most than most code readers!).

 

yeah it was the garage that put they plugs in mate i'll give them and the leads a go and see what happens

 

alright mate changed the plugs and leads seems to be running fine now thank f**k fingers crossed it stays like that cheers mate

 

cool.