Rough idle after engine reaches operating temp.

[1st 5er]

79 528i with the ACV and Temp sensor under intake on left side of engine.

When it's cold it starts easily and runs perfectly.

It starts easily after engine warms, but as the subject indicates after warming,
it's like it's running on 5 cylinders when idling.

After getting above 1700 RPMs or so it runs perfectly even while warm.


I'm stumped.

I have:
Reset the AFM tracking arm to a clean unworn path.
Cleaned and adjusted the throttle body settings per instructions in Tech FAQ post.
New plugs.
New cap and rotor.
New air management hoses.
Set timing after doing all the above, again per Tech FAQ instructions.
When I pull the wires, at the distributor cap, from each cylinder while it's
running, it definitely alters the idle, and there is a good volume of spark.

Have not replaced the wires.
Edited to add: Checked wires for spark quality and they all appear to be good.

New 02 sensor installed, slight improvement.
When I unplug the Temp switch it runs extremely rough, the first time I unplugged it the motor died immediately.

Bad ECU? I don't have a known good one to do the swap test.

[alotawatts]

...and you've looked this over ?
http://www.firstfives.org/faq/aux_air_v ... valve.html

[1st 5er]

...and you've looked this over ?
http://www.firstfives.org/faq/aux_air_v ... valve.html

Yes, the article, but have not yet tackled the job of trying to diagnose it as I've not been able to locate the two hoses that go to it.

This'll be my next project.

Now that I've read it again, tell me if I'm right in my understanding of it's function;
It's reduces air flow after warming allowing for proper fuel/air ratio according to ECU output.
If the air is more than the ECU is supplying fuel for then the lean mixture would cause poor operation of the warmed engine?

If this system was bypassed altogether would I have poor cold engine operation and normal warm engine operation?

[Lenny D.]

...and you've looked this over ?
http://www.firstfives.org/faq/aux_air_v ... valve.html

Yes, the article, but have not yet tackled the job of trying to diagnose it as I've not been able to locate the two hoses that go to it.

This'll be my next project.

Now that I've read it again, tell me if I'm right in my understanding of it's function;
It's reduces air flow after warming allowing for proper fuel/air ratio according to ECU output.
If the air is more than the ECU is supplying fuel for then the lean mixture would cause poor operation of the warmed engine?

If this system was bypassed altogether would I have poor cold engine operation and normal warm engine operation?

Actually it increases (metered) air during warmup to compensate for thick oil/cold engine parts for driveability factor. The valve then closes depending upon cylinder head temp. and a 12v. signal that slowly closes the valve via a bimetallic spring (and expecting you're driving the car normally to achieve *normal* warmup). The valve receives no signal from the ECU.
It sounds to me you have a problem with your coolant temp. sensor. That DOES send a signal to the ECU telling it how warm your engine is (supposed to be). A bad sensor or engine ground or the connector and/or wiring will send a false signal. The O2 sensor can adjust for a pretty large window of error, but only to a point.

The achilles heel of the FI system for our cars is this microvoltage variant potential under which it operates. Age, grounds (most likely), wiring and the connector all figure in and have a significant impact. The coolant temp. sensor can be tested for values, it's just a big thermistor. Book says normal indoor temps. should read 3Kohms. Fully warm - 400 ohms.

Check the FPR, but they are reliable and usually fail rich.

[1st 5er]

The coolant temp. sensor can be tested for values, it's just a big thermistor. Book says normal indoor temps. should read 3Kohms. Fully warm - 400 ohms.

So similar to the E28 readings?

14F(-10C) 8200-10500 ohms
68F(20C) 2200-2700 ohms
176F(80C) 300-360 ohms, fully warmed up

I got these from a thread over on MyE28.com and had previously posted here asking for confirmation.
Thanks for the reply.

I'm not real good with the ohm meter, although I do have one, so I'll try getting readings and also clean and reattach the grounds I can find.

Thanks for the input.

[Karl in KS]

Remember that any vacuum leak will let in unmetered air, especially at high vacuum--idle. And it will be more noticeable with a warm engine because the engine is set to run rich when it's cold, so the unmetered air will have less effect.

Since the whole crankcase runs at vacuum, even something as sneaky as a valve cover gasket or main seal can be a vacuum leak.

[1st 5er]

Remember that any vacuum leak will let in unmetered air, especially at high vacuum--idle. And it will be more noticeable with a warm engine because the engine is set to run rich when it's cold, so the unmetered air will have less effect.

Since the whole crankcase runs at vacuum, even something as sneaky as a valve cover gasket or main seal can be a vacuum leak.

I've sprayed carb cleaner all over the engine and hose connections with no idle changes at all.
Is there another or more accurate method?

Discussion is also going on over here in a hijacked thread.

[1st 5er]

Well, I did the deed, adjusted the valves, a loose 12 / tight 13, cold, and a little improvement, but not fixed.
When cold, it's pretty good, but after warming to operating temperature, same old shit, just not as bad.
The valves were definitely a little tight, all except one was a very tight 12, closer to 11.

Like stated earlier I readjusted the AFM again and still, symptoms remain.
The AFM wipe strip is pretty worn down on the lower side. The wear strips indicate it'd been adjusted several times.
I have several E28 M30 AFM's that are known good but none will work, all have the 4 wire connector, where the E12 M30 has the 6 point connector.

I've also, as mentioned before, changed out the temp sensor, all ignition parts except wires, they all tested good though, adjusted timing and rechecked it several times.

Connected positive to O2 wire and negative to ground.

Results:
At idle it fluctuated between 0.78 and 0.18 volts.
When I removed the oil filler cap on the valve cover it would drop drastically.

Driving fluctuated between 0.78 and -0.04 volts.
The higher numbers while accelerating, mid numbers while cruising, and lower numbers in a no load condition such as coasting to stop, between gear shifts, etc.

AFM???

[Lenny D.]

First - My preference for valve adjustment producing a smooth (enough) idle and good top end performance for a stock M30 engine is a snug .012, looser you loose top end, tighter increases the lumpy idle as Lambda 'hunts'.

Second - For all you've done you should have this licked. But - I would be very meticulous about 1) ever-so-tiny air leaks (search the FAQ), and having eliminated that, I would find the ground wire(s) on the right rear of the intake mainfold, chop off and replace the ring terminal. SOLDER the new, fresh wires (there are at least 2, maybe 3) to the new terminal. Those are 1) the ground for the coolant temp sensor, and 2) the ECU. According to the Bosch yellow book on L-Jetronic, nothing else should be attached to this ground point. Having done that, you want to make sure your 1) engine ground is solid and 2) your battery ground is solid also.

Third - Most importantly, to check/adjust the AFM via the O2 sensor output, it must be temporarily DISCONNECTED from the green wire feeding the ECU. If not, Lambda is in action and all you'll see is the 'hunting'.

[1st 5er]

Over the weekend, picked up a 1980 528i Automatic donor. (Going to be parting it out if anyone is interested.)

First I removed the AFM, adjusted the swipe arm, installed in my car, no real improvement.
Based on that I'm going to rule out the AFM being the problem.

Now I am in process of changing the Aux Air Valve
from the old style, my current '79 under the intake manifold setup,
to the newer on the valve cover version .

I removed the Aux Air Valve from the donor and began to examine it.

When cold, the valve is open, but only partially, probably about 1/3 of the way.
I can take a screwdriver and it freely rotates to the 'all the way open' position,
but when loosening and moving the 7mm adjusting nut it will not go to the complete open position,
1/3 open is about the limit. Is this a problem?

When the unit is heated, I tested it, it closes all the way. So, this is a good thing, right?

With it not opening 100% when cold, yet closing 100% when hot, is it usable as is or should I replace it?

First - My preference for valve adjustment producing a smooth (enough) idle and good top end performance for a stock M30 engine is a snug .012, looser you loose top end, tighter increases the lumpy idle as Lambda 'hunts'.

When I replace the valve cover to accommodate the newer AAV I'll be rechecking the valve adjustment.

Second - 1) ever-so-tiny air leaks (search the FAQ), and having eliminated that, I would find the ground wire(s)

Taken care of. When I remove the valve cover oil filler cap, the motor idle deteriorates even more.

Third - Most importantly, to check/adjust the AFM via the O2 sensor output, it must be temporarily DISCONNECTED from the green wire feeding the ECU. If not, Lambda is in action and all you'll see is the 'hunting'.

This link is what I was referencing for the AFM adjusting.
I've done nothing more than move the swipe arm.
I don't know what/how to do more than that, per your above remark. Is this in the FAQ's and I overlooked it?

I appreciate all the feedback thus far.

[Lenny D.]

The newer style (non-Jules Verne type - air only) is not supposed to be fully open cold. New ones I have purchased over the years are, from the factory, only open, as you state, about 1/3 with the outside ambient temperature in the comfortable range. Put it in the freezer for 1/2 hr. and it probably will close fully.
The reason for this is there is a fuel-cutoff function built into the ECU that does just that above a pre-programmed RPM at idle. What this means is what others have experienced with surging/dying condition at idle while the engine is in warmup phase. If the AAV allows TOO MUCH (metered) AIR to pass before it can close (i.e., 'catch up' to the engine warming) you will experience this surging effect. Put it back like it was.
And I doubt your complaint is associated with the AAV. At worst, a malfunctioning AAV will result is poor idle after startup during warmup (not enough metered air) or a fast idle after warmup (valve not closing in sync. with warmup - you can experience this by temporarily leaving the 12v. connector unplugged. The engine will idle excessively high until the HEAT from the valve cover closes the valve via the bimetallic spring - it is a dual-actuated function device).

I suggest obtaining a copy of the yellow book from Bosch 'L-Jetronic' to thoroughly understand the components and the system as whole.

Also, please read the post I left here on FF from the folks at Metric Mechanic on AFM calibration, and the correct use of the O2 sensor as a diagnostic tool: http://www.firstfives.org/bboard/viewtopic.php?t=186

My gut hunch tells me you have 1 - a pesky unmetered air leak (lean condition) 2 - an incorrect AFM adjustment (likely, resulting in a lean idle condition) or 3 - a wiring problem (lead, ground, oxidized connector associated with the coolant temp. sensor (read my previous post). L-Jet relies on microvoltage to perform correctly. Any tiny variance upsets this significantly.)

What happens when, at idle, fully warm, with your complaint present, you push slightly on the door in the AFM? If the engine happily perks up, you have a lean condition to figure out. If it gets worse and wants to/dies, you have a rich condition, but you will smell that.

[1st 5er]

Thanks Lenny,
Later in the week I'll do my homework and report back.

[Karl in KS]

Let's go way out on a limb and check the o-rings that are supposed to seal the dip stick....

[alotawatts]

Lets go out on another limb and POLL how many E12 owners have a perfect idle.

Ill start. My 79 is the best but it has a quick falter about every 3 seconds.

[1st 5er]

Let's go way out on a limb and check the o-rings that are supposed to seal the dip stick....

ed... O-rings? So the electrical tape wrapping isn't EOM? ed.

When I saw this, BTW thanks Karl, I went and checked the condition of said o-rings and, well, you see what I found.
When I pulled the dipstick out the car nearly died, so I'm guessing the electrical tape was doing it's job.
I left the dipstick out and placed a plug over the dipstick tube to totally seal it and find no improvement.

Now I am in process of changing the Aux Air Valve
from the old style, my current '79 under the intake manifold setup,
to the newer on the valve cover version .

This project has been completed with noticeable improvement, but still not 100%.

My gut hunch tells me you have 1 - a pesky unmetered air leak (lean condition) 2 - an incorrect AFM adjustment (likely, resulting in a lean idle condition) or 3 - a wiring problem (lead, ground, oxidized connector associated with the coolant temp. sensor (read my previous post).

1 - I'm ordering new intake manifold gaskets and fuel injector seals. I'm sure the injector seals are pretty decrepit
as there is an ever so slight change in idle speed when carb cleaner is sprayed on them.

2 - This should happen over the weekend, time permitting.

3- Taken care of, cleaned, replaced, etc. with no positive results.

What happens when, at idle, fully warm, with your complaint present, you push slightly on the door in the AFM? If the engine happily perks up, you have a lean condition to figure out. If it gets worse and wants to/dies, you have a rich condition, but you will smell that.

Will address this test this evening.

I suggest obtaining a copy of the yellow book from Bosch 'L-Jetronic' to thoroughly understand the components and the system as whole.

Also, please read the post I left here on FF from the folks at Metric Mechanic on AFM calibration, and the correct use of the O2 sensor as a diagnostic tool: http://www.firstfives.org/bboard/viewtopic.php?t=186

Thanks. This info will be included in the weekend effort.

Lets go out on another limb and POLL how many E12 owners have a perfect idle.

Ill start. My 79 is the best but it has a quick falter about every 3 seconds.

This should be interesting?

Again, thanks for the input, if only you'd come and do the work too.