M20b20 rough idle and misfire

[Onure30]

I have a E30 89 320i and recently i put a new battery on it and started it up,
Its runs really rough and there is misfire when reving it,
On idle you can see the car shaking side to side, i fitted a icv from a e36 recently as the old one was shot. No air leaks as i just changed over the intake boot and new crank breather hose.

Where can i start to diagnose the problem?

So far checked:
Spark plugs
Coil
Dizzy cap
Ht leads
New afm

[Speedtouch]

You probably need to disconnect the battery for a while to reset the ECU, reconnect it then let the car idle for at least 10 minutes or so to let the ECU learn its base idle settings. Then switch off and take it for a drive throughout the rev range.

This ensures full data transfer from the EPROM chip to the processor.

Another thing to check is the blue temperature sensor near the thermostat; if it's failed, it will cause the engine to run too rich, fouling the spark plugs.
https://www.e30zone.net/e30wiki/index.p ... emp_Sensor

[Onure30]

Thank you,
Ill replace the blue sensor and try again, fingers crossed its that sensor..
Ill also do the ecu learning procedure but i wouldnt be able to drive it as it needs work and cannot be driven.

Any else to look out for? What would the symptoms be of a leaking or bad injector?
When i removed the spark plugs they where black and slightly moist.

[Speedtouch]

Yes, if the spark plugs are black/moist, it's a sign of over-fuelling, i.e., running too rich. Another thing to check is that the HT leads are fitted in the correct order, and are of the correct resistance, though if they are new as you say, they should be fine.

Which ECU do you have? The later 0 261 200 380/381 versions had extra diodes in the idle control circuit that are prone to blowing, which could cause the issue described.

[Onure30]

Yes, if the spark plugs are black/moist, it's a sign of over-fuelling, i.e., running too rich. Another thing to check is that the HT leads are fitted in the correct order, and are of the correct resistance, though if they are new as you say, they should be fine.

Which ECU do you have? The later 0 261 200 380/381 versions had extra diodes in the idle control circuit that are prone to blowing, which could cause the issue described.

I will have a look and get back to you, im not sure on the ecu number.

[Onure30]

[Speedtouch]

Looks like an earlier pre-facelift Motronic 1.1 (0 261 200 163) ECU - unusual, on a 1989 car, where most were Motronic 1.3 after 1988.

[Onure30]

I dont know much about these german cars, im more into jap cars.

This is what its showing on reg check.
so being a 1.1 motronics does that have the extra diodes?

[Speedtouch]

The good news is, that the M1.1 doesn't have the extra diodes and is generally reliable, though with less resolution than M1.3, meaning it will inherently run slightly rougher or more 'raw' - not necessarily a bad thing.

[Onure30]

I think i found what my problem might be,
The fuel return inside the tank is completely clogged up, ive been trying for days to slowly push the gunk out but no luck,

Anyone have any tips on getting this line to free up?

[Speedtouch]

I would spray a degreaser in there - something like Gunk or carb/brake cleaner, followed up by ideally using a garage airline on it (or even a garden water sprayer or similar pumped up to create air pressure), being careful not to damage anything with too much pressure.

[Onure30]

Update:

I have now changed the fuel tank with a 55l and new blue temp sensor and the problem is still there,

It cranks and starts for around 10-15seconds and cuts off again, but when i start it up and hold the accelerator itll rev but sound really rough, its like a misfire.

Ive checked for leaks and nothing,
Ive changed over afm with another one and its seems to make a slight difference but nothing major.
I took the throttle body off and cleaned it. (Had oil inside it running down into the intake boot)
Removed injectors and cleaned them and put new orings and caps.
Im also using a icv from a e36 i dont know if that would make a difference.
I dont know what else can be the problem.

[Speedtouch]

If it won't hold an idle, I would suggest that perhaps the E36 ICV isn't right for it - for instance, it may have the wrong impedance. I would swap in a correct part and see if that makes any difference before doing anything else...

Another thing I would check is the compression of the cylinders, to ensure they are more or less equal and of good pressure - at least 130psi or so. Remember to hold the throttle open while cranking the engine when doing this.

[Onure30]

I just put everything back together for a smoke test , im getting smoke from the oil cap.
Does the caps have rubber seals on them as mine didnt.

Can the oil cap be the cause of all my problems?
Would that cause the engine to misfire and run rubbish?

[Speedtouch]

E-bay item no. 174624306835 shows a selection of E30 caps, to compare yours against...