New-to-me 1992 735iL – the fun begins!

[Cactuar]

E32FAN it's not only the rough idle I am trying to fix though, it's especially the idle that goes up and down.
I heard plenty of M30's on Youtube and they exhibit a varying amount of roughness. All of them would be tolerable to me.
But I haven't heard a hunting idle like mine. IMO it's too annoying and unusual to put it in the "they all do that" category.

Actually there is an idling M30B35 on Youtube that idles like my car, but it's on a Megasquirt ECU.
The RPM range and hunting frequency are almost exactly the same.
I would have liked if the author posted how he fixed it!

[CroughtonE32]

OK..............this wasn't easy in my overcrowded garage, but no extra room for cars with Covid supplies. Here's my Cold Start after 3 days.

[E32FAN]

Hi Cactuar,

This is an illuminating video clip! The cause looks to be the surging Air Fuel Ratio! It runs from 13.8 up to Redline at 16.2, right along with the surging idle.


The ICV can obviously cause, this and I have no idea what else could cause it.

This link https://www.diyautotune.com/support/...ng-megasquirt/ says:

Leaving the idle in open loop (warmup) mode will let you rule out one cause of an oscillating idle and let you get just the fuel and ignition side straightened out. As a rule of thumb, trying to use closed loop settings to compensate for poor fuel or timing settings will have the ECU chasing its tail, but never really catch it. You may find the engine runs perfectly well in open loop and you don’t need closed loop, particularly on a race car with no air conditioning and few electrical loads.

So I agree with a777fan's suggestion to remove the ICV connector and let it run with no DME command input. The ICV airflow vane will park in some arbitrary position, although it might be blown full open (or closed) by intake airflow.

I have seen very sluggish ICV vanes, that can turn very freely after carb cleaner treatment. Perhaps the DME is pulsing hard on the ICV until the vane breaks free, and then the idle surges.

Just sharing some thoughts.

[m60power]

OK..............this wasn't easy in my overcrowded garage, but no extra room for cars with Covid supplies. Here's my Cold Start after 3 days.

Nice video. Your E32 is so clean, it looks like it's in amazing condition!

Cactuar - I agree that something is abnormal with your idle; I doubt it's a 'typical' quirk of the m30 motor. I would do the same things trying to chase down the culprit.

[Cactuar]

m60power: glad I'm not crazy for chasing after a decent idle!

So I got the intake manifold out and cleaned it thoroughly using lots of elbow grease (and some degreaser). It's looking nice and clean.
intake_cleaned1.jpgintake_cleaned2.jpg

I have a question about the head on my car. I see a few dark stains along where the head meets the block.
Should I be concerned about them, or is it normal for an old engine like this to be stained in such a way? Thanks

20201013_014651.jpg20201013_014603.jpg20201013_014555.jpg

[a777fan]

I don’t see anything abnormal in your pictures. Are you referring to the darker shade of the block relative to the head? Or something more specific?

[Cactuar]

Yes the darker shades is what I am referring to.

[CroughtonE32]

I'm going to suggest that since you have the manifold off, (and it looks great) before you put things back together I would get the two hoses that go from the ICV to the center back of the manifold and the J shaped hose that goes from the back of the purge valve to the only other connector inside the manifold. They're not expensive and you'll never have an easier time to replace them. Tough to get to with the manifold on. A leak in either of these small hoses could affect your idle.
Jeff

[Cactuar]

Thanks for the tip Jeff, but I already changed those hoses (and the two small ones).
I did it with the manifold still in the car too! I still have battle scars on my hands

[a777fan]

Yeah. That darker stuff is just accumulated junk from over the years. Should clean up nicely with some degreaser.

I think m30 blocks are painted black, but someone with one would have to confirm.

[CroughtonE32]

So for a look at the color of the M30 block. This is the best I can do. When we broke everything down up top I took about a dozen pictures. I think you're correct. If the block was new I think it would be black. Other than some surface rust and at the time of this picture about 25 years of ageing, it seems to be so.

[Cactuar]

Yep Jeff mine looked a bit like that. It cleaned right up with some degreaser.

Received a small bundle of parts from the dealer today:
2 x transmission mounts
1 x power steering belt bracket
1 x AC belt bracket
1 x plastic coolant hose holder/clamp (I broke mine when doing the water pump)
20 x wave washers for the intake manifold nuts (two washers got lost during the job, ordered a new set)

20201015_192823.jpg

[CamE32]

Jeff, your idle (& overall condition of your car/engine bay) makes me drool.

I'm with you, Cactuar, that there is SOMETHING that must be causing our rough/hunting idles. I sincerely hope the intake gaskets turn out to be the cause. I've replaced or thoroughly tested dang-near everything else, and you have too!!!

-new fuel pump (along with the gas cap & fuel tank in my case)
-new fuel pressure regulator & filters
-ALL intake hoses/vacuum lines replaced
-distributor cap/rotor replaced twice
-spark generator (cleaned with electrical contact cleaner & also swapped with my parts car - no change)
-plug wires replaced
-3 sets of OEM plugs, all gapped correctly
-2 valve adjustments, including a new valve cover gasket
-injectors serviced by Mr. Injector (perfect flow report)
-ICV (cleaned but also swapped with my parts car and another I have from my first E32 - no change in idle, but slightly better throttle response with the original to my car, which has the lowest miles)
-TPS (swapped with my parts car, ohm tested, cleaned, audible click, adjusted correctly - no change)
-AFM (swapped with my parts car, ohm tested, cleaned - no change)
-voltage regulator replaced (steadied the voltage & raised it, but no change in idle)
-CPS replaced
-oil pan gasket (mine had a piece missing after sitting for 12 years, but upon replacing there was no change in idle. Still holds true after my incompetent mechanic replaced it a 2nd time to stop an oil leak caused by them never tightening the bolts to spec after the 1st time...)
-fan clutch replaced
-DME coolant sensor replaced
-DME itself (swapped with parts car, no change in idle)
-fusible links (I haven’t replaced mine, but you have, and mine appear OK)
-battery terminals & grounds cleaned/inspected
-O2 sensor replaced

At this point, what else is there besides the intake gaskets!?


On another note:
I removed the intake from my first '88 735i when I did the head gasket, but I don't recall any special tips for removing the hard-to-reach bolts. All I know is my 16-year-old sized hands might have helped... but I certainly didn't have a crow's foot or any other special tools. I somehow did it with only standard sockets and wrenches. I took a video of the first-start after replacing the head gasket, featuring my late father who got me into German cars (he owned 5-6 W126's and a nearly-identical-to-mine '88 735i purchased for $950 shortly after I got my first one for $850 lol). Watching it now makes me cringe... pretty sure I messed up the timing by 1 tooth, and for some reason - I will never forget this - the power steering pump was 100% dry after the 2 months it took me to do the head gasket. There was no leakage at all (where did all the fluid go!?!?!?), but it was completely dry after 2 months & was making a horrible sound I discovered shortly after the end of this video - still baffles me.


Keep the faith. We'll get to the bottom of this.

[Cactuar]

Cam you can add the intake manifold gaskets to the list of "fixes" that do nothing
I just finished installing the new gaskets and my idle is exactly the same as before.

When I initially started the car it stumbled badly and the idle was very rough: I immediately suspected the injector connectors (I hate these plastic connectors). Sure enough, the #6 connector was pushed out of the actual wiring casing so the #6 injector had no power.
And even when the car was running on 5 cylinders, the idle was hunting. It seems like the car doesn't really care how many cylinders are firing, the idle will hunt regardless.

I'm eating two slices of white bread with nutella on them to cope with the deception of this fix not working, haha.
I need to sleep on it and think of more potential causes.

Btw Cam did you replace the pieces between the brake booster and the intake manifold? Hoses, check valve, booster gasket/grommet etc?

- - - Updated - - -

Btw regardless of the small mistakes you did you should be proud of changing a head gasket at 16!! That's a great accomplishment most people haven't done in their lifetime, let alone under the age of 20.

[Cactuar]

Hey look the car can be driven too, not just stand in the garage with the hood open!
It was good to drive the car again. Still need to finish restoring the chrome molding on the rear door.

20201018_151652.jpg

[a777fan]

Isn’t it weird how sometimes you forget these things actually move?

Glad to see it on the road.

[Cactuar]

I tried disconnecting the connector to the ICV and I think the surging is gone? Hard to say for sure because the idle is much worse. When I connect it back the RPM rises, then comes down and stabilizes a bit, then the surging comes back.

I removed the air cleaner assembly to watch the vane of the AFM, while the ICV was plugged in. When the idle surges I can see the vane opening much more and I can hear air getting sucked in. I thought that during the idle routine, the air came from the ICV only? Or does the air come from the AFM and the ICV supplements it? Not sure if it matters in the end.

[zapass]

What I noticed during my investigation is that whatever I disconnect: FPR vaccume hose, ICV plug, temp. sensor plug etc. - rpms get stabilized. When I disconnected mentioned vaccume from FPR I was sure I found the source. Just before ordering new FPR I measured fuel pressure - was perfect.
My theory is whatever "nosie" you put into the system - lack of signal from sensor, huge leak - you run out from the area where all those parameters are somehow "unlucky", balance between them is subtle. Of course there needs to be something out of spec that is a cause.
Does it make sense?

My conclusion for now is that this issue is temperature related. I tried to heat up termostat housing and intake manifold using heat gun, before starting an engine. I was afraid not to burn something so in the end it gave me no result.

[CamE32]

I tried disconnecting the connector to the ICV and I think the surging is gone? Hard to say for sure because the idle is much worse. When I connect it back the RPM rises, then comes down and stabilizes a bit, then the surging comes back.

I removed the air cleaner assembly to watch the vane of the AFM, while the ICV was plugged in. When the idle surges I can see the vane opening much more and I can hear air getting sucked in. I thought that during the idle routine, the air came from the ICV only? Or does the air come from the AFM and the ICV supplements it? Not sure if it matters in the end.

good thinking to remove the air cleaner and watch the AFM! From my understanding, your assumption about air for idle coming from only the ICV should be correct. But maybe I’m wrong.

so if we’re wrong and the ICV shouldn’t be the sole source of idling air, then perhaps what we need to do is ever-so-slightly adjust the stopping point of the throttle body vane/flap thing???? I.e. to let enough air in to supplement the ICV so it’s not constantly trying to compensate??!

if not that, then is it possible our AFMs (& the one from my parts car) have lost some of their spring-e-ness? Or perhaps the ICV is being fed erroneous signals from the DME for some yet-to-be-explained reason? Hoping some of our resident electrical experts will chime in...

maybe we can convince Jeff to remove his air cleaner and film the AFM’s behavior at idle...

[Cactuar]

Ok I did a few tests tonight... I removed the idle air control valve from the system and unplugged it.

I capped the hole on the side of the large intake boot, where the IACV draws its air, and also capped the end of the hose where the IACV would send the air into the intake manifold. This resulted in a no start, obviously. No air = no start.

Intake boot capped, but now the hose was half way open. This resulted in a successful start but the idle hunted at a more rapid rate than I'm used to. Idled rough too.

Intake boot capped, hose fully open. The car started, hunting seemed to be gone, and detonation could be heard occasionally from the open end of the hose. Loud stuff!

Fun experiment. If the IACV is out of the system yet the car still hunts when 50% air is provided, it would mean that the hunting comes from somewhere else right? Maybe a sensor is sending the wrong information, or the DME interprets the correct sensor data incorrectly.

I'm not sure if there are more conclusions to draw.. any ideas?

[shogun]

Limited Operating Strategy (LOS) , here details from M1.1 and M1.3, all the same procedure for all the DMEs : In the event of a serious fault in one or more of the sensors or their wiring circuits, Motronic will substitute a fixed default value in place of the defective sensor. This procedure is often termed limp home. A serious fault occurs when the signal from the sensor is outside of its normal operating parameters. When operating in LOS the engine may actually run quite well with failure of one or more minor sensors. Since the substituted values are those of a hot engine, cold starting and running during the warm-up period may be less than satisfactory. Also, failure of a major sensor, ie the AFS, will tend to make driving conditions less easy. Once the fault has cleared, Motronic will once more accept the live signal from the sensor. The following LOS measures are taken in the event of a failure
Component..............................Action
AFS........................substitute values are calculated from the TS position. The load signal is fixed to 6.0 ms and the ignition timing to 20° BTDC once the TS contact is open.
ATS .....................substitute value of 50° C . A code will not be set, and LOS will not commence until a minimum of 3 minutes after engine start and the engine idling for a minimum of 30 seconds.
CID sensor.............injectors are pulsed simultaneously
CO pot..................substitute value of 2.77 volts
CTS...................substitute value of 80° C if ATS value is greater than 20° . if ATS value is less than 20° , substitute value of ATS value for first three minutes after engine start-up.
OS.....................substitute value, open loop control
TS.....................substitute values, restricted engine operation

[Cactuar]

Yesterday's tests generated a check engine light. Disconnecting the negative battery cable and reconnecting it made it go away.

[Cactuar]

I found an issue with my car not related to the idle, that's nice for a change.

When I pull the stalk to wash the windshield, the wipers wipe correctly but no fluid comes from the nozzles on the hood. However the headlight nozzles do spray, even though the headlight switch is off.
The hood nozzles used to work before so that's new. I'll get some leads to apply 12v to the pump to see if it responds.

[shogun]

which system do you have? duo pump, single pumps? I only know if from the 750. Over the years for the 750 they had different systems with more or less pumps.Actually 2,3 or 4
2: windshield washer + intensive cleaner
3: windshield washer + intensive cleaner + duo pump for headlight cleaning (starting xx/88)
4: windshield washer + intensive cleaner + two pumps for headlight cleaner (up to xx/88)

The windshield washer pumps are mounted in the tank next to the engine on the 750 unless if you have the headlight cleaning system. then the intensive pump is in the main reservoir and the headlight cleaning pump will be in the lower reservoir with the headlight cleaning pumps.

Or the washer nozzles are clogged. I once disassembled and cleaned them.

[Cactuar]

I have two water tanks, one for the headlight system on the driver's side, and one for the windshield on the passenger side.
The windshield tank has a level sensor and a pump at the bottom.
I don't have a tank for the intensive system, but... hmmm this makes me wonder:

500

Headlight Washer Sys/intensive Cleaning

Scheinw.waschanl./intensivreinigung

That's on my build sheet.
Does it mean I have the intensive cleaning system? Wouldn't there be an extra tank for it?