Mystery missfire.

[Fenrir]

Hi all,I have a missfire that i'm realy struggling with.
Symptoms,I cant seem to control the revs with the accelarator pedal up to 2,000rpm.
After 2,000revs the throttle acts as normal.
Conversly when running at motorway speed,and then reducing speed to urban roads 30mph,the car seems to hold back,its hard to explain but its missing at low revs,again at under 2,000rpm.
Another symptom is if i;m at moterway speed,and need to accelerate hard to get past someone the car coughs tiwce as if its not getting enough fuel,it then accelerates as normal.
Last symptom is if i sit in the car,watch the rev counter and gently blip the throttle to say 3,500/4,000rpm,the needle of the rev counter doesent come down in a smooth motion from 4,000 to 800/9000rpm.
Any tuners on hear that can set me on the right track. Iwould be most greatfull for you'r,thoughts.I have listed what i have allready done as bellow.

New coil packs,and checked ht loom where it runs through the inlet manifold,new plugs,air filter,new injecter seals,all vaccum pipes renewed,new o ring on vaccume tree where it joins engine,cleaned and tested IAC valve,cleaned and tested MAS seems to be working as when i remove the plug it haults and then stalls,probably missed a couple if things.Oh yes tryed higher octane fuel.Honestly its got me pulling my wig off.Hope someone can relate to my problem and has an answer thanks to you all.

[LeeT5]

Hi and :welcome:

I had a very similar fault just last week on my V70R. Whilst i appreciate it is completely a different car i will say just two things. Before i do may i say that the part in question had me scratching my ars@ for nearly three months!
Missfires can be caused by many hundreds of things and can manifest themselves in many weird and wonderful ways. It's important that you stay focused and KEEP THINGS SIMPLE! Do not assume it's something impossible because from my experience 99 times out 100 it never is.

You have missed one crucial component in your list and that is the Crank sensor. Do not waist time trying to clean it, just replace it. They are not expensive and can make all the difference.

The other thing is one component you have already looked at but i think it is the root cause of your problem. MAF sensor!!
I know you have checked it and unplugged etc etc...doesn't make any difference my friend. I too unplugged my MAF and the car would run but not very well. Some cars can run with or without MAF, problem is, it doesn't tell you jack. Just because you unplugged it and the car died, doesn't mean the MAF is ok!!! Does it?

My MAF cost £300 from the dealer after my car had ECM-130a logged in it for months. Trouble is, ECM-130a does not mean 'MAF sensor is pooped' It means '...loosely: the amount of air being monitored by MAF and O2 sensors alike, when added together, do NOT = the sum of Total air flow'. Basically it could be an air leak! So you see why i did not just rush out and buy a new MAF.

Anyways, new MAF fitted, codes cleared and boy, what a difference. Unbelievable. The Car idles perfect, does not hunt when slowing down and dipping the clutch, she pulls harder and stronger and the best bit is my fuel consumption has gone back down from 19.2 mpg to 25+ mpg. Happy days!!

To summarise: You need to replace your crank sensor (it will be shagged anyway) and have codes read by the dealer and i bet you need a new MAF.
Everything else you have covered.

Good luck.

[Fenrir]

Many thanks for the reply Lee,I have the Illexa Volvo fault code reader,there are no faults registered.Will give the Crank sensor a try first,and see if that makes a differance,i'm a bit loath to throw a £300 MAS at it just on spec.Some thing for the future mybee,the car drives well in all other respects,but you know what its like, if its not right, it niggles away at you,and you cant rest till you put it right.