Engine Misfiring every few seconds only on idle/warm

[paris]

Hi!

Have been trying to figure the source of a problem; Once warm AND on idle only (only when these two conditions are valid), engine starts to shake for 4-5 seconds and then becomes normal. After a while, it starts shaking again for 4-5 seconds and then again back to normal. It will repeat this for as long as the car is idle & warm. Looking for some ideas on what to look for, but before, lets see what we have replaced:

- All vacuum hoses, including those under the intake manifold
- Replaced Oil breather pipe
- New intake manifold gaskets
- Cleaned intake/idle valve
- run injector cleaner
- Replaced all fuel lines in engine bay
- New coil/spark wires, genuine bmw
- New rotor cap/shaft
- AFR Adjusted and report given to me by BMW tech
- New engine mounts & engine shock absorber
- Spark plugs are 2-prong Bosch, 30000km on them
- fuel pump replaced around 40000km ago with genuine BMW

Feels like the engine is misfiring that causes it to shake, but I'm really puzzled on what/where to look now. It's not gearbox issue as this happens on idle and in neutral

1989 / E30 / M40 / Manual /260000km

Thanks!

[cypriot_boy_2k7]

I had the same problem, never got to the end of it, I do have a feeling it is my fuel pump. Have you checked the blue temperature sensor on the cylinder head? Click on the wiki tab and search for blue temp sensor and it should give you a way to test the sensor and associated wiring.

[paris]

Does the temperature sensor on the head affect mixture preparation? I will have a look at it thanks! I will also need to have somebody check the fuel pump if its working properly, maybe change the relay as a precaution too

[Brianmoooore]

If your injectors are the originals, then they are long overdue for a rebuild. 'Injector cleaner' does nothing of any significance - they need to be professionally cleaned and calibrated.
If you're in the UK, see 'injectortune', in our traders' forum.
This may or may not cure your problem, but it's the first thing that needs to be done, to eliminate the possibility, and as a base point to set up the rest of the engine.

[paris]

Yes they are the factory injectors, never touched. Apart from normal servicing and a couple of water pumps & intake boots, all other parts are still original (until the service it's undergoing now). Unfortunately I'm not in UK but I will add the injector rebuild/calibration in the list too! Thanks

[paris]

Update:

New injectors solved the issue!