Poor performance
 

Hi, I'm new to this forum and I have read several threads that have similar symptoms to what I'm experiencing. My 320i coupe is experiencing random poor performance issues, when the problem is present the car will not accelerate and when I come to a halt the car will not idle and will cut out.

When it is running fine it has plenty of power. The car has been fully serviced etc, the Idle Control Valve has been removed and cleaned, the air mass meter has been replaced and there are no codes showing.

The car has 35k miles and apart for the performance issue the car is great.

Would anyone know any other areas I could check?

more info needed: When is this poor performance relevant - shortly after sitting overnight (cold) or after it's been driven awhile (warm)? Low speeds or at highways speeds? Acellerating or just crusing? Outside temps when this problem happens? -
*Have you checked for missing, lose or cracked vacuum hoses?
*Alternator belt tight & adequate battery power (11+ volts measured at battery)

As I said more info please. Drive it a week or so & DOCUMENT when it happens - that'll give us a better shot at helping you what to look for.

Thanks for the quick reply, I have checked all the hoses and have fitted a new alternator belt (a couple of months ago), the battery voltage while running shows 14.5v and 12+ while standing, the fuel pump and filter has been replaced.

The problem started about 3 weeks ago, occurring randomly, however it is getting more frequent. I can start the car and drive for up to 60 minutes normally and without warning the performance will drop, if I stop and turn the car off and leave it for 10-15 minutes and restart the car the problem will disappear. It does not seem to be affected by cold or weather.

No engine warning light or codes show up.

I hope this give more info.

How is the intake to the manifold? My car had cracks in that and these caused erratic idle. Maybe there is something similar that is affected by the engine heat

I don't think it is heat related, the problem has shown up when the car is cold, warm and hot.

Has the fuel filter been cleaned or replaced?

both the pump and filter have been replaced within the last 3 months ( the pump failed and needed replacing)

ok,so if the listed has been done - run a good fuel treatment through it - could be poor fuel, or condensation in the fuel. (Fuel quality is questionable these days - from all brands & grades) Bad fuel can also a ruin a good set of plugs - pull a plug and look it over - they could be loading up (black in color - soot build-up) - trying to help you without throwing parts at it + pillaging your wallet.

The plugs are showing the normal brown color, however I have new set. I will go through all the above again just in case they showed up fine on one of the car's good days.

Fuel pump relay? Fuel pressure regulator?

I have checked and cleaned the o2 sensor and ICT again, same problem. How can i test the fuel pressure regulator.

Could the catalytic converter be blocked and causing to much back pressure?

I suppose it could be the catalytic converter, but I'd think if that were the case a lotta other symptoms would show up, but I really dunno. Plus if it's clogged at that low a mileage something is way outta whack, a properly maintained and operated car wouldn't have its converter checking out like that, so soon.

Checking the fuel pressure and pressure regulator is covered in 130-10 and 160-8 of Bentley, and it's beyond my weekend mechanic abilities, you have to have or get a test gauge, fit a t-line to a fuel line, stuff like that, get voltage readings... Mechanic's territory so far as I'm concerned.

I checked the Cat and this is not causing the issue (a good friend let me swap the cat from his car, Also swapped the ECU, I owe him a few beers). Also managed to get a complete set of air intake hoses (from a salvaged car) Also no difference.

The last check I did has to run the car in the dark (very dark where I live in the countryside) and it appears that coils 1,2,3,4,5 are all arcing/sorting to the head, I will remove them tomorrow to see what the cause is. There could be oil in each plug channel

I will post with the outcome

I came across one source saying that finding oil in those channels is not uncommon (although I've been fortunate enough not to have experienced that myself). This source also said it doesn't seem to cause a problem with the plugs, which seems a bit of a stretch to me. Yeah, it'd be worth a look, just be prepared with something to sop up the oil while not letting anything fall into the cylinder if indeed you do find any.

^^^It's not a stretch. I've experienced it myself. The electrical contact is further up into the boot, and isn't in contact with the oil. This is, of course, assuming the usual seepage that can occur in that area. If your plug wells are filled high with oil, then you've got other problems to worry about than a leaky gasket :eek