E30 M325i engine troubleshooting

[nath 149]

I recently had fully lined up a good E30 Alpina in the UK to import, and a donor car here for parts or shell. Then my father passed away  unexpectedly and with that upheaval the big project wasn't a good idea, so I grabbed a local 1987 M325, with a few things that need ironing out.

 

Stumbling idle.

The car idles at a steady speed wherever set, but has a distinct stumble/misfire. No issues apparent at speed but it may be masked at those revs. Idles as if it has a lumpy cam.

• Valve clearances have been done
• Spark plugs replaced
• dizzy cap checked/cleaned- was new 10,000km ago
• injectors were apparently serviced and found to be clogged or grubby, fuel filter has been changed, presumable after that. All injectors are actuating.
• Vacuum leaks checked to a simple level, intake boot appears new as do various other parts.
• AFM has no flat spots and tests with steadily increasing resistance.
• Spark is apparent at all plugs
• Car has the two crank sensors on the bellhousing, an unexpected hall sensor on the harmonic balancer with cable up to the OBD plug(smooth rimmed balancer, where is the sensor picking a signal from?) and a sensor on one spark plug lead plugged to nowhere, I presume for facelift cars with newer motronic.

That is really my core interest. The metallic rattle from under the car could be an undisclosed lightened flywheel, a crappy input shaft bearing, throwout bearing or clutch springs, or simply the effect of a misfiring idle on those components. Am happy to have them all replaced.

Could the ECU (Motronic 1.0) cause this, even though the car basically runs well and there is no major misfire? Could the coil cause it? I'd not imagine it could being as it generally gets spark to where it needs to go.

 

Thanks

 

Nathan

Edited Monday at 07:22 AM by nath

[BMTHUG 1100]

hey bud. Check your your hoses for vacuum leaks, check also the resistance of the crank and reference sensors on the bellhousing, these can give a stumbling idle. Also check the resistance on your ignition coil. I have had  a few of these play up. Other things to check would be your idle control valve, take it out, clean it, make sure it's operating correctly with the correct resistance etc and check the intake house from your throttle body for cracks. Also the little pipes that come out the side of the throttle body need to be tightly fitted as they tend to have the knurled surfaces wear where they fit into the throttle body causing leaks. The sensor on the harmonic balancer is for the diagnostic port at the top of the engine and doesn't really do anything as far as connecting to the ECU. The plugs just go straight to the diagnostic port. Other things to check is pull out the oil cap while running and see how much crank case pressure you have, worn rings etc can make it idle funny if you're low on compression or there is blow by. Happy to check it out for you if you want to swing by my shop sometime in Glenfield. Love me a tech 1! I have one myself. Cheers 02102916373 SJ 

[BMTHUG 1100]

p.s yes the sensor from number 6 spark plug lead that has a plug on it will not be applicable to your pre-facelift car. Only the facelifts use this as part of motronic 1.3 engine loom 

[nath 149]

12 hours ago, BMTHUG said:

p.s yes the sensor from number 6 spark plug lead that has a plug on it will not be applicable to your pre-facelift car. Only the facelifts use this as part of motronic 1.3 engine loom 

Thanks SJ, I think you may have had his car in before? 

I’m keen to get her as nice as the B3, so one step at a time. Gotta sort out some original wheels first…

[BMTHUG 1100]

1 hour ago, nath said:

Thanks SJ, I think you may have had his car in before? 

I’m keen to get her as nice as the B3, so one step at a time. Gotta sort out some original wheels first…

Yeah I may of had it in my shop  before. Let me know if you end up selling the wheels on there. I may know a buyer