Hunting/Surging Idle

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bimmerjoe
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Hunting/Surging Idle

Post by bimmerjoe »

Hello all, I have done some searching about the surging idle problems others have had, and have not encountered the symptoms that I have been getting with my '82 633. When cold, it idles at about 1000 rpm, when warming up, after about 1 minute, it begins its surging/hunting/searching for an idle speed, it goes from about 1000 to 1400 and just keeps going, and going, and going. At first I thought it was the ICV, took it out and cleaned it with carb cleaner, no difference. Then changed the ICM, no change. Replaced two of the hoses that connect the ICV that were cracked/split. No change. Tried the TPS, no change. When I unplug the Coolant temp sensor over the thermostat, the idle holds steady at about 2000 rpm. (I also put in a new Coolant temp sensor) I am continuing to look for air leaks but in my searches on the forum, I also saw that some would test their idle by removing the dipstick to see if it was sealing properly. When I remove the dipstick, the idle surge lessens but is still present (only about a 200 rpm variation), so I then took a spare fuel cap I have and removed the oil filler cap, the engine immediately smoothed out and idles at about 1300 rpm. When I placed the fuel cap on in place of the oil cap, the engine surge returned. Removed the fuel cap, idle smoothed out to 1300 rpm again. Replaced the oil filler cap, idle went right back to surging. I have not had a chance yet to remove the throttle body & clean it yet. But is there anything else I should be looking at? Any info or ideas would be greatly appreciated!

Thanks in advance!

Joe
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86_6series
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Re: Hunting/Surging Idle

Post by 86_6series »

This is somewhat confusing, did you use the gas cap in place of the oil cap to see if
the oil cap was leaking vacuum?

So, do I have this correct-- with the oil cap removed from the cam cover--the idle is steady @ around
1300 rpm and no searching. With the oil cap screwed onto the cam cover the engine then searches and hunts.

Removing the oil cap causes a massive vacuum leak but the engine doesn't surge or hunt?

I've got to think about this more while others take a stab at it.
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bimmerjoe
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Re: Hunting/Surging Idle

Post by bimmerjoe »

Yes, that is absolutely correct. With the oil filler cap ON, the engine hunts & searches for an idle, when I take the oil fill cap OFF, the idle smooths out to about 1300 rpm, and is steady. No hunting or searching/surging for an idle...Very confusing to me, that's why I was looking to see if anyone else has experienced this. I am pretty baffled right now, hoping someone can shed a little light on this!

Thanks!
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86_6series
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Re: Hunting/Surging Idle

Post by 86_6series »

Strange that no cap, wide open leak, steady but high idle.
Cap on, hunting & fishing, damned if I can come up with any
reason for this, hope someone can come up with a possible cause.
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redrumm3
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Re: Hunting/Surging Idle

Post by redrumm3 »

This may sound simplistic but, there aren't any cracks in the rubber intake boot are there?
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Re: Hunting/Surging Idle

Post by muscam1 »

BimmerJoe - feel your pain. I've been helping a friend diagnose and fix the same exact thing you are seeing on an 83 633 - surging/hunting idle when warm. When cold, idle was fine. Removing the dipstick settled down the surging but left the idle high.

We went through some of the same troubleshooting as you but we couldn't figure it out so the car went to a local independent that "knows" these cars. "Supposedly" they have fixed the surging/hunting idle by adjusting the screw inside the ICV. Just saying... you may want to look at your ICV again. Know this surging/hunting is symptomatic of other problems. We don't have the car back yet to confirm since there were some other things the indy was doing to the car.

I have a thread on this forum on the surging if you want to search for it. I will close out that thread on what was done to finally fix the surging/hunting idle once we get the car back and can confirm it's fixed!

--Marc
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bimmerjoe
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Re: Hunting/Surging Idle

Post by bimmerjoe »

Redrumm- I sealed cracks in the intake boot on the top but I have not checked the underside recently. Will have to do so again. I continue to look for vacuum leaks but the going is slow because I am a little preoccupied with an engine swap in my e36.

muscam1- I have been watching your thread about this problem with great interest. When I had the car inspected at my local indy shop. The mechanic/owner that I know pretty well, is pretty sure it is the ICV. He suggested is remove it & clean it again and then try. However, he also told me that through the '80's & '90's, he has tried to fix dozens of them on BMW's, Audi's, etc, to no avail. He was unable to fix most of them. So once I get the engine swap on the e36 done I will hopefully get back into it.

Thanks for everyone's help & insight, I will keep you posted.
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Re: Hunting/Surging Idle

Post by bimmerjoe »

So I had a little extra time Sunday to do a little work on the 633. Removed most of the intake up to the manifold and cleaned/checked all the hoses, throttle body, ICV. All looked good and found no leaks as far as I could tell. Intake book checked out. When I removed the ICV, I could hear a tiny rattle inside and was not sure how the valve on the inside is supposed to move. I tried to gently work/move it with a screwdriver but it would not move. I did not put much pressure on it though. Is it supposed to move when not connected? I then removed/cleaned ground straps from the battery to the engine and body. No luck on any of it. Started the car, and within a minute when the engine warmed up, it went back to the throttle surge/hunting. As I let the car run longer, the speed to the surge & engine slowed. It went from about 700 rpm to about 1200 (before it was 1000 to 1400) After letting it run for about 5 min, I removed the oil fill cap again, but this time the surge/hunting continued, albeit not quite as badly. When I tried to adjust the TPS, as soon as I moved it a fraction, the idle jumped to a steady 3000 RPM. It did not matter where I adjusted it, the rpm were the same. If I turned it back to its lowest setting, the surge returned. So then just for fun, as the car was idling & surging/hunting, I unplugged the ICM and it had no effect at all, with the ICM unplugged the car ran exactly as it had done with it plugged in. I then went to the engine & unplugged the coolant temp sensor and the idle jumped to 2000 rpm & was steady. It had done this before as well. Then I decided to pull the vacuum hoses off 1 at a time to see the effects. There were no changes except for when I pulled the hoses from the ICV to the intake boot. Then the car stalled. So I am really at a loss here. Could it be as simple as the ICV? Don't really want to purchase a new one for $300+ if I am not sure it is the problem. I did take a video of the surging/hunting but I am still trying to upload it. Hopefully I will figure it out soon!

Any Ideas?

Thanks!
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Re: Hunting/Surging Idle

Post by ssf1342 »

I had a high idle issue on my '88 w/m30b35 after the car warmed up & driven around (a little above 1k when in D & 1400 when in P). I'm not sure what specifically fixed the issue, but I ending doing the following at the same time:

1. Replaced the two o-rings on the engine oil dipstick (it was very loose; there wasn't any friction when taking it out or reinserting).
2. Discovered that my cruise control cable was not connected to the throttle body, so reconnected that.
3. Also discovered that the purple-green wire that connects to the harness that plugs into the evap purge valve under the throttle body was broken, so had to solder that back together.
4. Replaced the hose from the intake manifold to the bottom of the ICV (this was the original reason for doing the work; I found the other issues along the way). This hose was rock solid & missing a hose clamp on the intake manifold end but no cracks found.
5. Replaced valve cover breather hose & plastic elbow that connects to the throttle body boot (hose was also rock solid but had small cracks).

No high idle issues since.

I see you have an older model, so some things may not apply but maybe something will help. The ICV you should be able to open the valve with your fingers. If you shake it I think the rattling (if it is a dull sound) is just the valve.
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bimmerjoe
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Re: Hunting/Surging Idle

Post by bimmerjoe »

ssf: I am unable to move anything in the ICV. The rattling inside sounds more like a small piece of broken metal or a little stone. I was unable to move any part of the valve inside the ICV. All of the hoses mentioned were checked, no cracks, all soft & pliable. Also replaces the seals to the dipstick. All had little to no effect on the surging/hunting idle. Thanks for the info! I appreciate it!
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bimmerjoe
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Re: Hunting/Surging Idle

Post by bimmerjoe »

OK, so after a long winter storage for the 6, I was finally able to remove it from hibernation and start working on it again. Still cant stop the surging idle, did find a ICV valve, helped a little, but just took the car about 3-4 min longer to start searching/surging. So a buddy of mine with an e28 was looking at it, could not find any vacuum leaks (again), and he pointed to this little plug up by the A/C tank near the fire wall. He said "what about the O2 sensor"? I said "where's that?", he pointed to this little white plug with a green wire leading back to the ECU and a small black wire leading under the motor. He unplugged it, motor smoothed out to 1100 RPM and stayed there, about every minute it would drop to 700RPM and then back to 1100. Plugged it back in & back to 1100RPM. Does anyone know if that sounds like a bad O2 sensor? I will send a picture of it asap. Thanks in advance for any ideas!

Joe
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bimmerjoe
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Re: Hunting/Surging Idle

Post by bimmerjoe »

633 O2 Sensor 3.jpg
633 O2 Sensor 3.jpg (86.2 KiB) Viewed 7021 times
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Re: Hunting/Surging Idle

Post by Doctorbeer »

If you've never taken out the O2 sensor, I would do so and take a look at it. The real way to test it though is to take a multimeter and check the voltage it gives while running around 2500 rpm for a few minutes. It's suppose to fluctuate in voltage. TBH, they aren't that expensive for the universal ones from Bosch or Denso and it's an easy job to do.

From your post and previous posts, when you said you check for vacuum leaks, did you hose it down with some sort of brake cleaner, starter fluid, etc? When I had to search for vacuum leaks, I drowned it in cleaner at every spot that could possibly leak and found a few. Injectors, crankshaft housing, valve cover etc etc.

A few oddity spots on my car.

Oil pressure switch at the top
My throttle position sensor's oring was worn out and leaking. Big leak, 5 cent oring fixed
Down below under the manifold, there are 3 tubes that lead to different spots(Fuel pressure regulator, cabin sensor, engine housing(???)), I was missing the one that lead to the cabin temperature sensor. This was a huge leak
The oil dipstick has two orings, make sure they are still there
Your rubber 'accordion' connecting to the throttle housing, the connections that plug into it may still be leaking despite feeling tight.

Pull the rubber boots back on connectors and make sure the wires are not broken. I've had almost all my plugs with broken wires. (The TPS, Coolant sensor, etc)

Yes, your ICV is suppose to rattle when shaken. When I was checking mine, I took a 9v battery and blew into a hose to make sure it was controlling the flow and actually doing what it's suppose to do when power is applied, not just making a clicking noise to trick me.

For me, it ended up being a lot of things wrong. I also did a test on the Air Flow Meter to make sure it was giving correct readings. I did end up opening it and cleaning it / adjusting it since the PO messed with it. Video below. I should note, don't make adjustments to it until you're pretty sure you have all the leaks fixed.

https://www.youtube.com/watch?v=hQYRep6K15k
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bimmerjoe
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Re: Hunting/Surging Idle

Post by bimmerjoe »

Doc, thanks so much for the extra information. I have gone through the top of the motor with brake cleaner but did not check as well for leaks under the manifold. I did have one tube off and reattached but it didn't make a difference. I have ordered a new O2 sensor, accordion boot and breather valve hose from Blunttech. One I change these I will go back to the injectors, oil pressure switch, valve cover, and under the manifold to check those areas more closely. Thanks again for the info! I appreciate it!

Joe
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Re: Hunting/Surging Idle

Post by Ralph in Socal »

You mentioned the ICM previously. It is typically the cause of hunting/surging idle
DE7353D4-AAF9-4A87-94B8-3BC05CAD6C45.png
DE7353D4-AAF9-4A87-94B8-3BC05CAD6C45.png (1.08 MiB) Viewed 6851 times
O2 sensors are cheap and easy to replace, they do wear out and they provide critical input to the ecu. I would replace it immediately

The ICV will rattle when shaken but a better test is to unplug it while the motor is running. The idle should increase when unplugged and then decrease when plugged back in. Good luck

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