1985 635CSi E24 - Rough Idle & vacuum hose kit

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cornwallis
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1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by cornwallis »

All - I’ve been slowly getting my car back into a daily driver after being overseas for a few years. Dealing with rough idle now after car is warmed up. Not repeatable always, here’s what I observed — I lose rpms at red light and have to give it gas, then rpms go up, then fall very quickly. Not driveable. Idle rpm can be erratic. After I let it cool several hours, it responds much better. It’s starts up fine when cold. Problem seems to come when warmed up after city driving. Note: I never drained my fuel tank after returning from overseas. A few questions for group:

1. I’d like a start with vacuum system. Has anyone installed the HPSI motorsports vacuum hose kit - any feedback? They have excellent article on troubleshooting, so I’m starting with this. Hoses are very likely original so I think it’s good idea anyway.

2. Will also look at air-side and filter. Any other preventative maintenance on air side?

3. What can I do on the fuel side? I’ve never drained the fuel tank. Or messed with injectors. Is that straightforward? Pumps are a few years old. I’m getting fuel. When it’s cold I can drive it no highway and it’s responsive.

As always appreciate feedback!
Hector :twisted:
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1985 635 CSi, Auto
emac
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by emac »

If the car has been sitting a long time it may be time to just go through each system. New plugs, wires, hoses, etc. Smoke test to check for air leaks. Fuel system cleaner for injectors and clean out idle control valve. Sometimes its a combination of little things that add up to poor running.

I just bought a Stringer Brand smoke tester. I haven't used it on a car yet, but it is well made for the price and would be handy for your situation.
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cornwallis
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by cornwallis »

Thanks emac, I saw a couple of videos on the smoke tester, that looks sweet. I’ve started replacing some electronics, ign coil, plugs, etc but more to do. I’ll start with the vacuum hose kit and idle control valve. Thanks for suggestion to clean it, didn’t know they could be cleaned. I may get the stinger smoke tester eventually. :D

Also ran across this thread of similar issue: https://www.bimmerforums.com/forum/show ... tical-idle
Hector :twisted:
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cornwallis
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Re: 1985 635CSi E24 - Rough idle & thermovalve

Post by cornwallis »

Have started troubleshooting the air/vacuum system and found the thermovalve didn’t pass function test when the engine was warmed up.

Does anyone know how to clean or refurbish these?

They are not cheap, range from $130-150. if anyone has a functioning one you don’t need, I’d be happy to give you some $ for it. Part # 11741264132. I have a 1985 635CSi, coupe, Auto.
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Hector :twisted:
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Ralph in Socal
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by Ralph in Socal »

As emac said, you could have multiple little issues that combine to cause the rough unsteady idle. The 85 did not have a separate idle control unit so the ecu controls the ICV. Unplug the ICV while the motor is running and idle should increase. If not there’s a fault in that system

Also make sure your throttle body is clean and the butterfly gap, along with the throttle position sensor, are set properly. Buildup in the throttle body will cause idle issues

You can drain the majority of old fuel by disconnecting the outlet of the fuel pressure regulator at the end of the fuel rail and routing the output to a suitable container. Either run the engine or bypass the fuel pump relay with a jumper wire

Send me a PM with particulars and I’ll get a thermovalve to you next week. I haven’t touched that system for a while but I think it’s just for the gas tank evap recovery system. Memory has failed before so I could be wrong. Good luck

Ralph
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)
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cornwallis
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by cornwallis »

Thanks Ralph, appreciate the feedback! I think you’re right, I’m seeing lots of little issues so far - hopefully will add up to making an improvement.

I’m on step 2, page 13/67 of (https://www.hpsimotorsports.com/motronic). so far I’ve found cracks in the intake boot (after air filter), and the straight boot after the airflow meter. I’m going to replace them with new parts.

I’ll reach out to separately on the thermovalve, which also failed.

Haven’t gotten to the ICV yet. Will test that shortly.
Hector :twisted:
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cornwallis
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by cornwallis »

All - want to share what I did to fix rough idle:

1. Replaced the vacuum lines (see pic below - all the blue lines are new). In the process, I found several lines were dry rotted or cracked.
2. Replaced the thermovalve - thanks Ralph! :-)
3. Replaced the 90-bend rubber fitting (after the air filter)
4. Replaced the rubber boot (after the air flow meter)
5. Cleaned and removed the ICV - needed some TLC.

Car is running much much better now! Much more responsive and does not have an erratic weak idle when it warms up.

Cheers!
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Hector :twisted:
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emac
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by emac »

Great job, glad its idling better. I see a blue hose running from the coolant resovoir to the radiator. Make sure it is rated for that application (heat and pressure). That hose is different than the typical vacuum hoses.
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cornwallis
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by cornwallis »

Good point. I checked online and found temp rating of 338 F, but no mention of pressure rating. Will keep an eye on it. Thanks for the excellent comment!
Hector :twisted:
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KINGJOHN808
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by KINGJOHN808 »

Aloha. Did the kit from HPSI come with different sizes of hose? I want to change all of the vacuum lines under the hood because there are several cracks. Where did you source the other rubber bits as well?

Mahalo’z.
Ewa Kai, Hawai’i
1984 633CSi
1983 633CSi (wreckers)

“Aloha and have a great day!”
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cornwallis
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by cornwallis »

Hey Kingjohn,

The HPSI kit does come with 2 different hose sizes, it gives you instructions for each hose, where they are located.

It took me about 2 hours to do. There are around ~12 hoses. 1 or 2 of the hoses was quite difficult to access, as it was under air manifold and if have big hands, just use patience. Removing is easy, reinstalling the silicon hose is tougher. ](*,)

The rubber boots after the air filter, I sourced from AutohausAZ, got OEM parts.

8DEE11A1-B847-46DB-A7E1-D0888EE6D86E.jpeg
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Good luck!
Hector :twisted:
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KINGJOHN808
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by KINGJOHN808 »

cornwallis wrote: Fri Jun 11, 2021 10:41 am Hey Kingjohn,

The HPSI kit does come with 2 different hose sizes, it gives you instructions for each hose, where they are located.

It took me about 2 hours to do. There are around ~12 hoses. 1 or 2 of the hoses was quite difficult to access, as it was under air manifold and if have big hands, just use patience. Removing is easy, reinstalling the silicon hose is tougher. ](*,)

The rubber boots after the air filter, I sourced from AutohausAZ, got OEM parts.


8DEE11A1-B847-46DB-A7E1-D0888EE6D86E.jpeg

Good luck!
Aloha!

Finally got around to replacing the vacuum lines that i sourced from HPSI. Was just as easy as you mentioned. I do have a question though, what is the blue line that you have going into the cab? I replaced all the vacuum lines that I could locate, most of my “fluid” hoses were new or recently replaced.

Mahalo’z.
Ewa Kai, Hawai’i
1984 633CSi
1983 633CSi (wreckers)

“Aloha and have a great day!”
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cornwallis
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by cornwallis »

the blue line going into the cabin starts from the manifold and goes into cabin (open ended under the steering wheel) I believe it is used for ambient air/fuel adjustment during idling. It was part of the kit.
Hector :twisted:
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Re: 1985 635CSi E24 - Rough Idle & vacuum hose kit

Post by hornhospital »

That line going to the driver's compartment is supposed to connect to the ambient air temperature sensor on the under-dash panel. It draws air past the sensor, and the sensor feeds the ambient air temperature info to the climate control system, adjusting the heating or cooling accordingly.
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'85 325e "Hazel Ann"; '95 M3 "Ashlyn"
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