Mystery connectors in engine bay

[Freight]

Wondering if anyone can help me figure out what these mystery connectors and stud are for. I found out my air box to the *not MAF*(?) bracket has been hitting the valve cover to the point it sounds like a loose heat shield, and that lead to discovering the airbox was cracked. Temp fixed that, but gonna tig weld the crack and rivet for support to help the spot welds. In doing that, I discovered some mysteries.

Firstly, the alternator bracket seems to have a floating stud. Nothing connected to it, and it doesn’t feel loose. 
 

this is at the passenger side of the firewall, seems to come from the loom, and seemingly both ends could connect?
 

Yes, it was snowing as I was wrapping up. Here’s another floating plug, seems to be coming from the fuse box loom. Resembles a large JST plug.
 

Does this fuse box region situation seems normal, aside from the random loose relay? Am I missing a part?
 

Lastly this is the floating relay. I looked at the fuse box/relay diagram the other day trying to figure out what it’s for, but I’m a little slow and at a loss. Looking up the relay number yielded nothing but a possibly match for an e36 fuel pump relay?
 

Thanks guys

[Blue Shadow]

The aux fuse box is not positioned correctly, it is where that dangling relay is supposed to be attached to the main box.  I don't have an aux fuse box but it is usually on the short side of the main fuse box. 

The ETM says the relays next to the connector are the fuel pump relay and the oxygen sensor relay.  Expect it to be one of those

The stud on the ac compressor support is for a nut of some kind.  Our cars did not have anything connected there.  Similarly that 2-conductor plug is not connected along with a few behind the gauge cluster.  

I think the white one is the oxygen sensor connector but I'd have to check.  




 

[4DSC]

On my car the dangling relay you show is mounted on the fuse box where your aux relay box is and it has a little tab on it for the aux fuse box to clip into so they are "stacked" 2 deep away from the fuse box. I also have the orange connector sitting around in the same area and don't know what it's for. The green wire connectors is for lathe O2 sensor but I recall it being on the driver's side for some reason.. maybe there are 2?

[Mike W.]

The second one is easy, that's for the oxygen sensor. It should be connected, the

white part to the connector inside the boot.

[Aldo525]

Yes, it was snowing as I was wrapping up. Here’s another floating plug, seems to be coming from the fuse box loom. Resembles a large JST plug.
 

 

 

 

There is a 2022 post asking about the same flat yellow connector (#5):

viewtopic.php?t=158826

Looking the 86' 535i ETM I found (not an exhaustive search) the only one VI + VI/YL wires combination where the colors and number that each cable has in the connector match: Related to the ACC "Safety Switch", Fuse 11 and to a not used SRS connector.

[Freight]

The second one is easy, that's for the oxygen sensor. It should be connected, the

white part to the connector inside the boot.

Interesting. I’ve got no issues with the way the car runs, should I expect a change? If it weren’t so cold, I would get the car up in the air and locate the o2 sensor. Is there a sensible reason one might have their o2 sensor unplugged or wired in an alternate way that would explain it being unplugged?

im not in a state with emissions inspection 

[Freight]

The aux fuse box is not positioned correctly, it is where that dangling relay is supposed to be attached to the main box.  I don't have an aux fuse box but it is usually on the short side of the main fuse box. 

The ETM says the relays next to the connector are the fuel pump relay and the oxygen sensor relay.  Expect it to be one of those

The stud on the ac compressor support is for a nut of some kind.  Our cars did not have anything connected there.  Similarly that 2-conductor plug is not connected along with a few behind the gauge cluster.  

I think the white one is the oxygen sensor connector but I'd have to check.  





 

I’ll look at moving the aux over, though in looking for pictures of the stock layout online, almost all photos show it located where it is in my car. Someone’s been in there and mucked about so I’ll figure out what’s up

[Mike W.]

The second one is easy, that's for the oxygen sensor. It should be connected, the

white part to the connector inside the boot.

Interesting. I’ve got no issues with the way the car runs, should I expect a change? If it weren’t so cold, I would get the car up in the air and locate the o2 sensor. Is there a sensible reason one might have their o2 sensor unplugged or wired in an alternate way that would explain it being unplugged?

im not in a state with emissions inspection 

It might result in a smother idle since it wouldn't be using the always changing O2 input. But at the expense of increased emissions and poorer gas mileage. Sometimes they run a little better with it disconnected, sometimes worse. But even if passing smog isn't required, why pollute more?

[Freight]

Interesting. I’ve got no issues with the way the car runs, should I expect a change? If it weren’t so cold, I would get the car up in the air and locate the o2 sensor. Is there a sensible reason one might have their o2 sensor unplugged or wired in an alternate way that would explain it being unplugged?

im not in a state with emissions inspection 

It might result in a smother idle since it wouldn't be using the always changing O2 input. But at the expense of increased emissions and poorer gas mileage. Sometimes they run a little better with it disconnected, sometimes worse. But even if passing smog isn't required, why pollute more?

I only mention the lack of smog here because its not likely anyone was struggling with emissions - so it’s unlikely anyone was trying to mess with anything emissions related unless it was running poorly. I like clean air, it won’t be staying disconnected permanently.

it idles beautifully, literally rock solid at 650-700ish, zero hunting or pulsing. Gas mileage seems to be pretty good too, at least on the highway. I do seem to have some bucking/lurching in 1st/2nd coming on and off throttle though…in reading tonight, I wonder if someone unplugged the o2 sensor trying to improve that, and found some level of improvement but never bothered to touch the tps/icv. I’ll plug it in tomorrow and see how the car behaves. If it’s worse, I’ll disconnect it and circle back to it once I deal with the on/off throttle issue

[Blue Shadow]

Check your external relays for the friction fit connections, the angled ridges that interlock.  

There should be a female to match the male on the fusebox and a male on the other side to allow the aux fusebox to attach.  Maybe some gorilla work broke the connector tabs for this, leaving the dangling relay, dangling.  

If so, maybe you can swap the two relay positions and have a connector location for the aux box.  

[ahab]

The O2 sensor connector is there for testing and diag purposes. Under normal circumstances you'd leave it connected.

[Freight]

Check your external relays for the friction fit connections, the angled ridges that interlock.  

There should be a female to match the male on the fusebox and a male on the other side to allow the aux fusebox to attach.  Maybe some gorilla work broke the connector tabs for this, leaving the dangling relay, dangling.  

If so, maybe you can swap the two relay positions and have a connector location for the aux box.  

The slots on the relay were both fine, so I ended up putting the relay onto the fuse box and then connecting the aux box to the relay. No idea why the last person to fool with it didn’t just connect them together.

what’s the aux box for Anyway? 

[Freight]

Interesting. I’ve got no issues with the way the car runs, should I expect a change? If it weren’t so cold, I would get the car up in the air and locate the o2 sensor. Is there a sensible reason one might have their o2 sensor unplugged or wired in an alternate way that would explain it being unplugged?

im not in a state with emissions inspection 

It might result in a smother idle since it wouldn't be using the always changing O2 input. But at the expense of increased emissions and poorer gas mileage. Sometimes they run a little better with it disconnected, sometimes worse. But even if passing smog isn't required, why pollute more?

So I connected the o2 plug, and I can hear a slight shift in idle smoothness, but it’s minor at best. The needle doesn’t even register it. With it unplugged, it’s smooth and returns to idle perfectly, and finds idle upon cold start very quickly. With it plugged in the idle hunts a tiny bit but otherwise I don’t see any difference, both cold and hot. 

I also tried unplugging the TPS, and the idle doesn’t change(audibly, a tiny bit) nor does there seem to be any change in the on/off throttle jerk at slow speeds. With and without o2. Only change is when it’s unplugged, open the valve cover cap causes the engine to die. With it plugged in, the car will stumbled for a couple seconds but will keep running. 

I guess that means the TPS is good and well adjusted?

[4DSC]

Checking the TPS and adjusting it is pretty simple and takes 3 minutes with a multimeter. Covered in Bentley and a video that was recently posted in another thread by a member.

On the throttle on/off jerkiness, it could be something idle circuit related. I have this as well on my car to some extent but only below 1500 RPM which is when I understand the ICV can start kicking in. Isn't there also a cutoff for when the car will stop firing the fuel injectors/spark if decelerating with no throttle and rely on the motion of the drivetrain only around this RPM?

[Freight]

Checking the TPS and adjusting it is pretty simple and takes 3 minutes with a multimeter. Covered in Bentley and a video that was recently posted in another thread by a member.

On the throttle on/off jerkiness, it could be something idle circuit related. I have this as well on my car to some extent but only below 1500 RPM which is when I understand the ICV can start kicking in. Isn't there also a cutoff for when the car will stop firing the fuel injectors/spark if decelerating with no throttle and rely on the motion of the drivetrain only around this RPM?

That’s my understanding of the icv operation also. Today I’m going to dive into the ICV itself. That’s the rpm range where I experience it as well, and likewise my understanding is that it does cut off fuel - that can be seen when the economy needle swings fully left, rather than floating just past 40. 

[Mike W.]

On 059 ECU BMWs I've had, 1300 on the tach was the cut in cut out speed. With the idle switch activated, RPM would not rise above 1300. It could try to surge, hit 1300, then cut out to cut back in when idle speed dropped. Got to be a fuel cutout.

On/off jerkiness can be caused by misadjustment of the TPS, the idle switch has to open as soon as the throttle is opened, not just close at idle. You can run into a situation where the ECU sees idle by the switch, but you foot has put some movement into the throttle, so nothing until it's wider open than you want.

[Freight]

On/off jerkiness can be caused by misadjustment of the TPS, the idle switch has to open as soon as the throttle is opened, not just close at idle. You can run into a situation where the ECU sees idle by the switch, but you foot has put some movement into the throttle, so nothing until it's wider open than you want.

Does it make sense that the jerkiness would diminish at higher speed? Or is that indicative of something more?

I need to put a multimeter on my tps still, but in reading about it, it sounds like if there’s no change at idle when unplugging it, it’s likely to be fine. Is that accurate?

[Mike W.]

On/off jerkiness can be caused by misadjustment of the TPS, the idle switch has to open as soon as the throttle is opened, not just close at idle. You can run into a situation where the ECU sees idle by the switch, but you foot has put some movement into the throttle, so nothing until it's wider open than you want.

Does it make sense that the jerkiness would diminish at higher speed? Or is that indicative of something more?

It makes sense that you would notice it less at higher speed. If you're at 5 or 10 MPH in a parking lot in first or even second gear, you're going to notice a change from idle to say 5% throttle a lot more than at speed. Ideally you would want to be able to go from idle to 1% throttle.

I need to put a multimeter on my tps still, but in reading about it, it sounds like if there’s no change at idle when unplugging it, it’s likely to be fine. Is that accurate?

In my experience the idle part of the TPS is very reliable, the WOT less so. But I think you're confusing the switch being good with it being in proper adjustment. A meter is better, but you might be able to adjust it by ear. It should click as soon as the throttle is opened just a tiny bit. That gives you a smooth transition.

[Freight]

Does it make sense that the jerkiness would diminish at higher speed? Or is that indicative of something more?

It makes sense that you would notice it less at higher speed. If you're at 5 or 10 MPH in a parking lot in first or even second gear, you're going to notice a change from idle to say 5% throttle a lot more than at speed. Ideally you would want to be able to go from idle to 1% throttle.

I need to put a multimeter on my tps still, but in reading about it, it sounds like if there’s no change at idle when unplugging it, it’s likely to be fine. Is that accurate?

In my experience the idle part of the TPS is very reliable, the WOT less so. But I think you're confusing the switch being good with it being in proper adjustment. A meter is better, but you might be able to adjust it by ear. It should click as soon as the throttle is opened just a tiny bit. That gives you a smooth transition.

This is a click than can be heard with the engine off, I assume?

I figured as much about being at speed. Today I’m going to get under the car and take a peek at the diff mount when I check the tps. I noticed the reverse clunk(it’s not new, I just have focused on other stuff) and searching last night, saw there may be some overlap in what I’m experiencing. If the diff mount is toast, I think it’s best I address that before messing too much with the engine. 

I really appreciate all your guidance 

[Mike W.]

This is a click than can be heard with the engine off, I assume?

Correct.

[Freight]

This is a click than can be heard with the engine off, I assume?


 

Correct.

Ended up not having time to check the diff but I check the icv and tps and both are perfect. TPS is perfectly adjusted

[4DSC]

On 059 ECU BMWs I've had, 1300 on the tach was the cut in cut out speed. With the idle switch activated, RPM would not rise above 1300. It could try to surge, hit 1300, then cut out to cut back in when idle speed dropped. Got to be a fuel cutout.

On/off jerkiness can be caused by misadjustment of the TPS, the idle switch has to open as soon as the throttle is opened, not just close at idle. You can run into a situation where the ECU sees idle by the switch, but you foot has put some movement into the throttle, so nothing until it's wider open than you want.

Mike,

Just wanted to thank you for this insight that seems obvious in retrospect. Specifically that if the TPS does not click open exactly when the throttle starts moving and lags behind, the signal triggers when the throttle is already slightly open. My TPS was adjusted very close to perfect but I was able to get it a hair closer with a little trial and error. It definitely helped with the on/off idle transition and now I think it's as good as it can possibly get. One of those cases where "very close" and "perfect" makes a difference for those of us who are always on the quest for perfection.

[Blue Shadow]

The aux box is for you to have an always hot and a hot when running fused location to add accessories. 

Check the ETM for hot when running, don’t know if it is unloaded for start.