Engine Stumbles Intermittently
BMW325e 1985, 5 spd, 293k
I need some suggestions about where to look for an intermittent engine problem.
Last summer I replaced my engine (thrown rod cap and holes in sump), with a used engine that came with the wiring harness, and manifolds. Engine runs well most of the time.
Occasionally, the engine will stumble, falter, and sometimes die. Waiting a short while, it regains its feet and is again running fine. Usually happens when slowing, as in approaching an intersection. This behavior is sometimes exhibited at start up, rough misfiring, then eventually smooths out.
The misfiring, stumbling, does not seem cyclical.
1. Have a smoke test done to locate air leaks.
2, The idle control valve should be buzzing quietly with the key to 'ON' engine off.
3, There are a pair of sensors in the bellhousing by the driver's feet. One tells the computer where the engine is in the firing cycle and the second tells the computer what the engine speed is. The connectors for these sensors are on the fire wall. A crude test for these sensors is to measure the resistance...values are on any E30 site.
4, Make sure that the engine coolant sensor is within resistance spec.
5, Make sure the ignition system is in tune.
6, make sure that the injectors are not leaking.
I've eliminated most of those items.
Don't know about the engine temp sensor yet.
Because it is very intermittent, goes sometimes days with no problem - running very well, I'm looking at things that seem like they might be consistent with that.
I think the speed and reference sensors you mention are possibilities. Their connectors at the wiring harness (mine are at a bracket on the valve cover) are all very badly damaged, enough so the connections are not secure.
Also wondering if there's a problem at or around the throttle body.
8 yrs. Has it been so long? I don't think much about the car(s) when running well. And for the E30, that's been almost 300k. I just like driving it.
I would check TPS ICV and AFM for a problem like this.
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