Rough Idle/ Cutting out.. Ideas?

[bowtie2bimmer]

I am posting this on behalf of AndrewM...

87 325e.

Symptoms are rough idle, ecomometer will read bad mpg. It will cut off when stopped. However the problem is intermittent. It will be fine for one drive and act up for another. Interestingly enough if I turn on the headlights the idle smooths out and everything goes back to normal...



Any ideas?

[jlevie]

If by "econometer reading bad" you mean that it drives towards zero during an event, I suspect a problem with the fuel system. Run the tests in the Bentley.

[dnguyen1963]

Rough idles = vacuum leaks
Eco meter erratic = SI board/batteries
Turn on headlights and everything is fine = BMW electric gremlins

[bowtie2bimmer]

I know he has used starting fluid and checked for vacuum leaks...

He also swapped in a different IACV...

[dnguyen1963]

Starter fluid is not a substitute for smoke test. You friend should not be doing anything else until all vacuum leaks are eliminated.

[andrewm]

While it might not be a substitute, the starter fluid test works pretty well. The catch is, the problem is very random and very intermittent. Not acting at all like a vacuum leak. So while it might be a vacuum leak, it's hard to get it somewhere to do a smoke test when it's unpredictable.

As far as econometer, it reads worse mileage. Approx 50% of what it normally would be. But then, if I turn the head lights on - the econometer then acts normally almost every time.

[dnguyen1963]

That is precisely the problem with vacuum leaks...intermittent. Many of the connections are old and seem to be tight visually, but when the car is moving these connections can become loose and create vacuum leaks. Smoke test under pressure will normally find these leakages.

As for the econometer, are you talking about the actual gauge or the reading from panel?

[andrewm]

The acual gauge on the cluster.

[dnguyen1963]

You might have to remove the cluster and exam the board under a magnifying glass for any cracks in solder. Clean all contacts and tighten up the ground nuts.

[andrewm]

well, the events are related. I highly doubt there's an issue with the SI board. the hesitation, and econometer work hand in hand. When I turn the lights on, most of the time it fixes both of the issues. See where I'm going with this?

[andrewm]

So, an update, it stalled on me again. I couldnt get it to start, so i unplugged the maf. Started right up, but i couldnt give it any gas or it would die. If i plugged it back in, the car died. Thoughts?

[dnguyen1963]

Your fuel/air ratio is messed up. I still think that you have some massive vacuum leaks. It is time to do a smoke test. I do not know why turning on the headlights fixes your issue though.

[andrewm]

Yea, I'm gonna try to get a smoke test done this weekend. My work schedule makes it impossible during the week. That and the fact I rarely drive the e30

[jlevie]

I do not know why turning on the headlights fixes your issue though.

That increases the load on the engine and the DME would respond by opening ICV further to increase mass flow. That in turn would increase the amount of metered air in comparison the un-metered air from the leaks.

[EH Motorsports]

That increases the load on the engine and the DME would respond by opening ICV further to increase mass flow. That in turn would increase the amount of metered air in comparison the un-metered air from the leaks.

Actually the dme will see a voltage change and increase injector duty cycle to compensate for the added load. Thus making a lean running condition better due to more fuel.