Engine rumble

[AngryJonny]

Hi folks. New member here from England... had my E34 for about 2.5 years and I love it.

Anyway, I'm not all that mechanically-minded but I have a small problem with my E34 and I was wondering if anyone here my recognise the symptoms or if it's a common fault.

Bit of background... the car is a late 1990 525i 5-speed manual. It has the M50 24v engine - one of the earliest I believe.

Anyway - I've just got back from a trip where I drove from London to Edinburgh and back - a round trip of about 900 miles or so. I had a full service done before I went on the trip and work carried out included a new idler arm and O2 sensor as well as all relevant fluids, filters and oil etc.

I noticed, especially after about 400 miles that the car developed an engine rumble, usually under light acceleration. The power would go down and the car would feel rough and unbalanced. This could be rectified by accelerating a little harder, where the car would "kick" and return to normal service. It felt as though the engine was running on only five cylinders when this rumbling was happening.

I first thought I'd got some bad fuel so next time I filled up I put in some Redex to clean the fuel injectors and smooth it out a bit but that did no good. The problem is only intermittent at the moment but I'd like to sort it out before it gets any worse.

It's crossed my mind that I may have a bad spark plug in one cylinder, a clogged injector or maybe a problem with the distributor? Does anyone here know what it might be, or what I can do about it. Is there any way to work out which cylinder is not firing? I can't feel for a cold pipe in the exhaust manifold because the car is fine under tickover.

Another thing... when the car was serviced the mechanic said that it needed a new breather-hose (?) but they didn't have one in. Could a bad hose be causing this? I wouldn't have thought so myself, but maybe.

Thanks in advance for your help.

Jon

[winfred]

i get everything back to factory fresh in terms of tune up items before pursuing the problem, on the m50 theres no distributor only coil packs one on each plug, id change the plugs and see if the valve cover is leaking oil into the coils (very common) and shorting out a coil, the coils themselves can fail under load and be hard to track down, any air leaks won't help

[AngryJonny]

Cheers for your help. I had the plugs replaced as part of the service so perhaps they've done something wrong. I'll check and see if they're all OK.

Would this cause the problem to sort itself out under heavier acceleration?