M10 rough running/repair log

[4bangerfury]

Trying to use a new thread to keep track of this issue.

It's a 1985 L-jetronic m10. I just replaced all the idle air and vacuum lines. Also put hose clamps on everything. It still has the same bucking issue intermittently. I really only notice it after the car has warmed up. When it's really bad, I can watch the econometer go to infinity when it shouldn't. Is that telling me there's still a vacuum leak somewhere?

I've removed the ac compressor and condenser, so I removed the ac idle increase as well. I figured it's one less source of leaks.

I was going to look for a new idle air valve, but it didn't match what was on realoem when I looked up my car's Vin. I had to look up the European 318i to get the right drawings of my idle air lines. Here is a pic of the motor before changing the air/vacuum lines:


Also, here are two connectors that don't go to anything right now. Does anybody know what they are supposed to go to?





I think all the parts I need are here to install a vacuum gauge and a fuel pressure gauge this weekend to try and get a better idea of what is happening when the bucking issue happens. Other things I'd like to get to this weekend is replace the intake manifold gaskets, replace the fuel filter, and replace the fuel injector seals.

[TobyB]

I can watch the econometer go to infinity

I'd say check fuel, but the econometer dropping strongly suggests that the ECU is either
losing power or cutting fuel 'intentionally' based on what it thinks is happening.

Because it sounds like it's losing a signal... making the ECU think the throttle's closed.
If the tach is stable, it's probably a fuel input.
If the tach drops, it's most likely the engine speed sensor- in the dizzy, I think- or
a power supply problem to the ECU.

If it's fuel, try checking the throttle position switches (4 cyl doesn't have a sensor... does it?)
and air flow meter.
Also worth checking the air and water temp senders for a loose/broken connection,
but it's probably not that.

hth

t

[4bangerfury]

It has a throttle switch. I've checked at the switch when I pulled the throttle body for cleaning and it checked out. Another thing I was going to check this weekend is the connection at the ECU.

Not sure about tach. It doesn't work right now. I was assuming the tach itself is bad, but I'll check the wiring diagrams to see if I can check the tach signal going to the instrument cluster.

[4bangerfury]

Definitely leaning towards electrical issue. The engine was barely staying alive on the way home from work after it warmed up, lots of stuttering/cutting out when I pulled over. As soon as I pulled over, she started running perfect. Checked for loose connections, found nothing obviously wrong, hit the road again. She ran like a champ the rest of the way home like nothing was ever wrong.

[Acet]

Faulty fuel pump relay? If it's intermittent then it will cause that random bucking of car. At least that what I experience atm

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[glnr13]

one of those two plugs goes to the idle control valve

[Acet]

I think 3rd image is the plug for ICV. The plug in second image is unplugged on my motor also. I'll snap a pic of the icv installed just for reference.

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[4bangerfury]

This isn't my ICV?:


Another thing I've noticed is it doesn't act up as much when it's colder out, which is going to suck because I'm in FL.

Other than that, there hasn't been enough time to work on this car. Had to work last weekend, and most likely this weekend as well.

[glnr13]

i'm not sure what that is but it's not the same ICV that i have and have seen on most US m10 e30's i've seen.

ICV for m10 looks like this:


to be honest, they don't work that well anyway. a lot of people delete them. I kept mine but did the "penny trick" using a washer.

[4bangerfury]

i'm not sure what that is but it's not the same ICV that i have and have seen on most US m10 e30's i've seen.

ICV for m10 looks like this:

to be honest, they don't work that well anyway. a lot of people delete them. I kept mine but did the "penny trick" using a washer.

Yup, looking up my car on realoem shows that style of ICV. I had to change my region from US to Europe to find the style that's actually on my engine.

http://www.realoem.com/bmw/showparts...48&hg=13&fg=15

[Acet]

Looks like it but my setup is slightly different.





Also, the connector that's near the firewall. Colors are blue and white if I remember correctly:






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[thebutterson]

I think what you have on your car is an aux air valve from an E21. They allow some air to bypass the throttle body during warm up by using a valve that expands closed as it heats up.

[gettinscurvy]

I also have an 85 m10 with a miscellaneous connector along the firewall that's connected to nothing. But...my car doesn't start, so who knows...

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[4bangerfury]

It's still an intermittent problem. I was checking wiring and found this little guy not in the connector:



It was the wire going from the closed throttle switch to the idle stabilization relay. Immediate results after were disappointing. After heating up, the car could not stabilize the idle with the throttle switch closed. Just barely opening the throttle made it run normally.

I left it like that, figuring I would just keep the throttle barely open on the drive to work this morning for now. Then everything runs fine this morning. No hiccups whatsoever. no idle issues. The car really does seem to run better when it's cooler outside.

I did order an ICV and idle controller supposedly from a running car. I figured it can't hurt to try.

What do you guys think about removing the aux air valve? It is connected to the wiring harness, so I'm wondering if it is being controlled or if it has a sensor and sending something back to the ECU. I haven't seen any wiring diagrams with the aux air valve in it.

[Acet]

It's still an intermittent problem. I was checking wiring and found this little guy not in the connector:



It was the wire going from the closed throttle switch to the idle stabilization relay. Immediate results after were disappointing. After heating up, the car could not stabilize the idle with the throttle switch closed. Just barely opening the throttle made it run normally.

I left it like that, figuring I would just keep the throttle barely open on the drive to work this morning for now. Then everything runs fine this morning. No hiccups whatsoever. no idle issues. The car really does seem to run better when it's cooler outside.

I did order an ICV and idle controller supposedly from a running car. I figured it can't hurt to try.

What do you guys think about removing the aux air valve? It is connected to the wiring harness, so I'm wondering if it is being controlled or if it has a sensor and sending something back to the ECU. I haven't seen any wiring diagrams with the aux air valve in it.

Glad to hear youre making head way! Maybe the dme needed some time to recalculate or reset something due to new signal,
Who knows? Hopefully it will resolve the issue, at least partially.

My m10 runs relatively well, considering that all plug threads are stripped and spark plugs are just sitting there, but after a lot of driving in traffic or when hot outside, my car acts weird like yours. Sometimes it just hickups but sometimes it looks like im banging the clutch pedal in 1st gear. Car jerks a lot and wont go anywhere. So anyways everytime this happens, I go under the hood and there is intermittent clicking from the black rectangular box which that plug connects to. Just throwing it out there..

I was reading some threads on here and saw that some people bipassed the electric vacuum valve (aux valve?) and ran the vac line straight from intake mani to vac advance on the dizzy. I did that and my car drives so much better now. I didnt notice that much difference in idle but engine is more smooth through out my crippled powerband. I think next ill delete the ICV and adjust the idle via throttle plate screw. The only downside of removing the icv from what I read was that you have to let your car warm up good on colder days.

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