Rough Idle and Power Steering Pump - connected?

[songzunhuang]

I've been battling a rough idle for a long time. I've tried just about everything and was just at my wits ends and decided to turn my attention to other matters. So there was the screechy power steering pump (and the associated leaky brake booster) to repair.

Two weeks ago, I completed the power steering repairs and something weird happened. The car appears to be idling smoother. Does this make any sense? Could the varying load of the power steering pump due to it sucking in air have caused a rough idle? Or is the change in load so minor that this couldn't be related?

I'm just curious what you think.

Also, this is how you know you've got a big air leak in the power steering system. I used to have small bubbles, but then I got the below. It's when I knew I had to take serious action.

A serious power steering system leak.

Foamy.png (1.47 MiB) Viewed 6753 times

[plip1953]

I've been battle a rough idle for a long time. I've tried just about everything and was just at my wits ends and decided to turn my attention to other matters. So there was the screechy power steering pump (and the associated leaky brake booster) to repair.

Two weeks ago, I completed the power steering repairs and something weird happened. The car appears to be idling smoother. Does this make any sense? Could the varying load of the power steering pump due to it sucking in air have caused a rough idle? Or is the change in load so minor that this couldn't be related?

I'm just curious what you think.

Also, this is how you know you've got a big air leak in the power steering system. I used to have small bubbles, but then I got the below. It's when I knew I had to take serious action.
Foamy.png

A power steering fluid smoothie!!

My money would be on there being no connection other perhaps than the more constant (extra?) load on the engine from a fully functioning power steering pump perhaps helping the idle control valve to do it job better. Have you tried switching on the aircon to see if what effect that has on the idle smoothness? And also if you place a big electrical load on the alternator?

As part of what you've done thus far, have you swapped out the idle control valve?

EDITED: Thinking about it, I'm rather less sure what I've said above it relevant to your model as I'm only (reasonably) familiar with late model 635s with Motronic.

[songzunhuang]

I've been battle a rough idle for a long time. I've tried just about everything and was just at my wits ends and decided to turn my attention to other matters. So there was the screechy power steering pump (and the associated leaky brake booster) to repair.

Two weeks ago, I completed the power steering repairs and something weird happened. The car appears to be idling smoother. Does this make any sense? Could the varying load of the power steering pump due to it sucking in air have caused a rough idle? Or is the change in load so minor that this couldn't be related?

I'm just curious what you think.

Also, this is how you know you've got a big air leak in the power steering system. I used to have small bubbles, but then I got the below. It's when I knew I had to take serious action.
Foamy.png

A power steering fluid smoothie!!

My money would be on there being no connection other perhaps than the more constant (extra?) load on the engine from a fully functioning power steering pump perhaps helping the idle control valve to do it job better. Have you tried switching on the aircon to see if what effect that has on the idle smoothness? And also if you place a big electrical load on the alternator?

As part of what you've done thus far, have you swapped out the idle control valve?

EDITED: Thinking about it, I'm rather less sure what I've said above it relevant to your model as I'm only (reasonably) familiar with late model 635s with Motronic.

Appreciate the brain cells you expended on my question. I have not tried the A/C since it's been quite chilly here in the California Bay area. I'll give that a go in my commute home today.

As for the idle control valve, I have every reason to believe it's not the culprit. I have taken it off twice to clean, inspect and generally monkey with it. It seems to have all of the right behaviors from what I can gather in postings on this board. The idle also changes noticeably if I unplug the ICV while the engine is idling.

Anyhow, although not silky smooth, my idle seems better and I'll just enjoy it while continuing to think about what I can do next to improve it.

[Rondel Fan]

Song,
I just finished working on my car and noticed the hose from the intake to the ICV was split near the ICV and was causing my newly erratic idle. Can you tell us what repairs you made to your PS system? My 1986 is leaky so I plan to rebuild the pump and possibly replace all the low pressure hoses. BMW list the hose PNs but I was wondering if generic hoses might fit the bill.
thx
Mike

[songzunhuang]

Song,
I just finished working on my car and noticed the hose from the intake to the ICV was split near the ICV and was causing my newly erratic idle. Can you tell us what repairs you made to your PS system? My 1986 is leaky so I plan to rebuild the pump and possibly replace all the low pressure hoses. BMW list the hose PNs but I was wondering if generic hoses might fit the bill.
thx
Mike

Mike, I replaced all the steering hoses with OEM BMW hoses. There is one hose with a hard line that I didn't replace, but it seemed in good shape still Other brands of hoses should work, but I gave up on the hit or miss deal with (coolant and fuel) hoses a while back. If you peruse my project thread, you'll see all the hit and misses I've had with aftermarket stuff.

As for the power steering, look at the last page of my thread. https://bigcoupe.com/phpBB2/viewtopic.p ... &start=750
I rebuilt everything. It wasn't too hard actually as long as you get the BMW rebuild kit. I think it was like $40.

As for my idle, I had the system smoke tested and there was no leak. I had the valves adjusted, but they weren't too far off spec. I've replace all the hoses here as well. Finally the independent mechanic I took it to removed a wiring harness that he says was for US Emissions, but didn't really help much. He indicated that it should run fine and still pass California smog test. It's a bit better now after service from the independent mechanic, but what actually caused the years of rough idle, the jury is still out. Now with this COVID thing, I've not driven the car much so I don't know if the latest fixes have taken. We shall see.