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Surging idle


Sidebp

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Hi,

My 3.2 has always idled a little fast at around 1,100RPM, bouncing to around 900-1,400 when starting.  In an effort to resolve, I removed my Idle Control Valve and cleaned it with some carb cleaner - doing so flushed though some relatively dirty fluid and upon refitting the idle seemed to be more stable. However I have just taken the car out and at standstill my revs have started surging between 1,300RPM and 1,700RPM, when driving, if I close the throttle it seems to have added about 300RPM and the car pulls slightly whereas before it would have bled speed.

From my limited knowledge I think there are a few next steps:

1) Try setting the idle RPM (potentially this was the issue in the first place and its now somehow been exacerbated by my cleaning efforts)

Potentially less likely:

2) Check the cylinder head temp sensor

3) Check the throttle closed sensor is correctly functioning

I am assuming points 2 and 3 are less likely given the minor issue I had to start with? Is it likely I have damaged the ICV and need to consider a replacement?

Any other pointers?

Thanks

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I doubt you will have damaged it, its a fairly simple valve and cleaning it with carb cleaner is a well trodden path. I would bypass it and set the idle, there is a proper procedure to isolate the ICV while you do this but I cannot remember what that it. I think it involves bridging pins somewhere on the engine bay fuse panel. I am sure someone will come along soon to fill in the gaps in my knowledge :)

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Thanks - the procedure is detailed in the Bentley manual so will give that a go first. 

Feels unlikely that the valve is damaged (it's still clicking when powered on),inlet and outlet seem tight but perhaps I have introduced a vacuum leak.

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Thanks for the replies. Had another poke around this evening and noticed that there is also a small 'bang' sound at the point of ignition, if I turn off the ignition and restart it soon after there is no bang (but the surging persists) - could the bang be due to over fueling/a rich mixture which subsequently gets burnt off?

 

Thanks

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In case anyone goes through a similar process I thought I'd keep this up to date.

Ive removed the valve given it a much more thorough clean. Connecting to a 9v battery the valve opens and closes so the next check is voltage on the feed and then a check on inlet and outlet vacuum feeds to ensure there are no leaks. I cleaned the hoses too and removed quite a bit of oil so perhaps the seal isn't as good as it was.

After that I will try to reset the idle speed.

Edited by Sidebp
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  • 2 months later...
  • 3 months later...
14 hours ago, Sidebp said:

Thanks for the reply.

All sorted with a reconditioned ECU (idle control pins were faulty).

did you also have a pop on downshift from the exhaust? what would be the ballpark price for the replacement please (hoping I dont need one too)

 

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Hi,

No pop that I can recall but it does that occasionally anyway.

Cost for refurb including life time warranty (apparently!) was around £450 - came back with a pre and post test report so good peace of mind.

I can dig out the name of the company who did it if you want.

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  • 1 month later...
  • 8 months later...

Message for Sidebp as I'm having similar idle and surging issues.

Help required with my 3.2

The cold idle on my 3.2 started to surge a few times before settling to a regular idle. The good old internet suggested taking the body of the ICV (idle Control Valve) apart and thoroughly cleaning it. I did this and then the car wouldn't start from cold and idle at all. I took the valve apart again and this time the car just kept surging... Foolishly I started to rotate the body of the motor in the valve whilst the car was running and the valve appeared to stopped working, as it stopped buzzing/clicking.

I then acquired a used Bosch ICV from ebay and asked the seller to test the valve by applying a voltage alternately between the centre live pin and the outer pins before I got it. The prescribed Porsche test. This was successful and I repeated the same test on receipt of the valve, which made me think this valve worked ok.

However, at ignition key turn this valve wasn't buzzing/clicking, just like the original had stopped buzzing. I put a volt meter across the ICV connector pins and it read 11 volts each side, so at least a voltage was present, though I didn't know if it was modulating. I therefore suspected I had blown a transistor in the ECM.

The car would start but just kept surging until it got warm.

The car has gone to a specialist Porsche garage and they have taken off and cleaned the throttle body and air flow meter, believing the original surging could have been due to an air leak, or contamination. They have also done the Porsche prescribed battery test on the ICV. But then put a scope on the ECM output to the ICV and got a square sign wave when the car was cold, suggesting there is a modulating signal going to the ICV! So why isn't the valve buzzing, working and allowing the car to idle properly when cold?

Apparently you can isolate out the ICV from a connector in the rear fuse box, this is used to allow correct setting of the idle speed. The garage have informed me that they can't isolate the ICV at this point!

The garage have said that not only isn't the ICV working, but they can't get the car to run twice the same each time they start it...

They have put the scope on the flywheel reference sensor and that is showing some interference in its pattern, so could be one of the issues. The speed sensor seems to be working as it should.

I'm thinking the only way of definitively determining if my ICV is working is to swop it over to another 3.2, to at least rule this in or out.

Could you please let me know what make your replacement ICV is and also the people who refurbed your ECM?

Many thanks in advance

Andrew

Worcestershire

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  • 2 weeks later...

Apologies for the slow reply and sorry to hear of your experience, I found the trial and error very frustrating - your symptom and story sounds very similar to mine.

I hypothesized that a previous owner manually adjusted the valve to compensate for a failed ECU in the past. When I cleaned the valve, I moved the vane from the position it had been set at causing the idle to increase. The ECU is programmed to intervene and cut the RPMs at approximately 2000RPM, when it drops back to around the 1000RPM mark (where idle RPM is set), the cycle repeats, resulting in surging. To confirm my theory, I disconnected the old valve and used a screwdriver to centralize the ICV valve, the gave a smooth idle. However, on colder or warmer days, the idle richness may be off, leading to either difficult starting or slightly high idling. I could probably have left the car like this as it made it driveable but felt it best to invest in getting it back to health.

  1. My issue was resolved by AutoUmbau an aircooled specialist (they are very good and have recent experience of this issue!). They swapped out the ECU with a donor car and the surging went away - the issue with my ECU was that the control pin was faulty. If your garage doesnt have much aircooled experience or access to donor cars/a parts bin then you can spend a lot diagnosing this type of problem.
  2. I think they used https://www.atcdrivetrain.co.uk/ for the ECU refurb - if you call them they are relatively laid back so may be able to confirm. A quick check on ATC's website and they do refurb Motronic ECU - cost was about £450 inc report and warranty.
  3. The valve I ordered was https://www.autosensorberlin.com/en/shop/idle-control/porsche-en/porsche-911-iac-0280140501/ (took about a week to arrive, in my case this wasn't the root cause).


 

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Hi Sidebp

Thanks for the reply and appreciate your help.

Update - I've received a new LOWE valve, just like yours, at the weekend. This morning I turned on the ignition and felt the valve for vibration, nothing. See video below just over 14 minutes in and the valve should apparently vibrate.  

https://www.google.co.uk/search?q=porsche+3.2+checking+idle+control+valve&sxsrf=APwXEdcfFB_EHuxV0VwQeD9WBlNFBK-PMw%3A1679931916129&source=hp&ei=DLohZKq1BoGVhbIPj6K3yAg&iflsig=AOEireoAAAAAZCHIHG5oqLdRhbmTJuEScMuVIDyc0Ovw&ved=0ahUKEwiq6-yIuvz9AhWBSkEAHQ_RDYkQ4dUDCBE&uact=5&oq=porsche+3.2+checking+idle+control+valve&gs_lcp=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&sclient=gws-wiz#fpstate=ive&vld=cid:c7f7a24c,vid:MRZG-s_55CU

 

Then tried starting the car two/three times and it wouldn't idle, just immediately died. Started it with some throttle pedal and kept it around 1200 rpm for less than a minute, then it settled to an idle just below 900rpm. 

Assuming this valve is fine it obviously isn't getting the correct signal to it, even though the specialist has seen a square sign wave at the idle control valve connector.

Could I ask a favour just to double check the video link advice. Would you turn on your ignition and feel your ICV to see if it does vibrate please?

Many thanks

Andrew

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Hi,

My ICV does vibrate now but didn’t before. The most useful test I found was:

1) Ignition off, unclip the top hose from the ICV

2) Disconnect the wiring harness from the ICV

3) Carefully use a flat blade screw driver in the top ICV inlet and move the vane to fully open or fully closed

4) Turn on power (but not ignition)

5) Look into the top ICV inlet and reconnect the wiring harness. It should swing to half open/closed and start shimmying to maintain position

If you can’t easily start the car then I suspect you will find that the valve is open or closed too much meaning there is too much or too little bypass air (because the ECU can’t set the position correctly). I got mine running by setting the ICV vane position manually to about half way and leaving the  wiring harness disconnected (remembering to reconnect the top hose!). This worked fine in most average conditions but per above wasn’t great as atmospheric conditions changed; likely in your case as the car warms the idle bypass mix changes enough to allow the car to run.

 

Edited by Sidebp
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Hi Sidebp

The specialist said much the same as you have written down. They left the one on it closed so it didn't rev too much at start up and required a little throttle input.

As I suspected it should vibrate. Obviously my ICV is getting the wrong sign wave signal.

Going to get my IT mate to have a look, he designs and programmes boiler controllers for Siemens. Hopefully just a blown transistor. 

Failing that its a call to ATC drivetrain.

Thanks again for your replies and help.

A

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  • 2 weeks later...

If it helps, I made this short video of my ICV behaviour:

https://drive.google.com/file/d/1-iWikEUfScTj5vwLgeCknR28vfyK5DgH/view?usp=share_link

  1. Valve set to closed manually
  2. Can see me connect wiring harness and it jumps to roughly mid point and starts shimmying

This was actually taken when it wasn't working properly but shows what I believe to be the correct behaviour; my issue was that it was inconsistent and sometimes would stay in the wrong position or didn't adjust as the car warmed due to a malfunctioning control pin.

Worth saying that my car still isn't perfect, resolving this issue highlighted that my MAF needs a recondition - can of worms but all part of TLC I guess!

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Hi Sidebp

My ICV issue gets stranger every time I've looked at it.

My IT mate came over and we took the Engine Management apart. Couldn't see any component that had obviously blown. We tested the relevant transistors and diodes and all seemed OK.

We put a scope on the ICV connector with the ignition on and it was producing a square sign wave something below 5volts per side. In theory you would think this should make the ICV vibrate, but it doesn't. I've tested all THREE of the IC valves I have and they will click side to side with as little as 3 volts applied across the middle and outer pins. The current ICV on the car is the brand new one!

I'm getting over 12 volts from the middle pin on the connector to ground and around 10.5 volts on a multimeter across the middle and each outer pin with the ignition on.

Why isn't my ICV vibrating and working??

Andrew

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Hi Sidebp

Yep i'm not getting anything. It doesn't click once, to open or shut the valve and it certainly doesn't hum, vibrate, shimmy - which is what it used to do before I buggered about... I twisted the body of the valve (when it wouldn't stop surging) and must have blown something in the process, as it was during this that it stopped vibrating!

My mate is having a think and has also emailed another chap he knows it R&D who works for one of the Bosch companies to get his opinion.

I've just put the multimeter across the central and outer pins with the connector off and the engine idling and I'm getting 12.5 ish to 13 ish volts each side.

Now according to a forum quote I can find online, the voltage between the centre and outer pins when the engine is running should be between 3 and 3.5 volts. Maybe this is the problem, something is making the connector get too much voltage.

Does anyone want to confirm this and put a multimeter across their ICV connector once the engine can idle OK?

Andrew 

PS Sidebp

I've had a look at your video and would concur that this is how I believe it should operate, with the valve mechanism 'floating' in the central position, hence the hum/vibration as it being held by a modulated voltage. 

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  • 4 months later...

Accumulated brain power needed…
 

Yesterday afternoon I had a problem with my idling speed. Would sit at around 1600rpm then drop momentarily to 1000 rpm. This morning runs perfectly at 900rpm.

It’s not the first time this has happened. It occurred previously a couple of years ago. 
 

Any chance that I can fault find?

 The Other Nige 

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