3.2 Carrera surging idle

[Sidebp]

My 3.2 had a slightly jumpy idle when cold so I decided to clean it with some carb cleaner. Reinstalled and now my idle is even worse, fluctuating between 1100 and 2000rpm (both when hot and cold).

So far I have:

- Cleaned the valve twice

- Fitted new jubilee clips (the old ones didn't hold the vacuum pipes very tightly)

- Tested the valve using a 9v battery (it opens and closes)

- Checked the ICV feed using a multimeter. Slightly oddly (and probably incorrectly, one negative pin gives me 12.4v, the other gave me 50v?!)

- Tapped the ICV when running to see if there is any change in RPM/if it was sticking

I am a little concerned that I can't hear the ICV buzzing when powered on but I can't necessarily see why the feed would be an issue given I only cleaned the valve.

Any suggestions on where to check next? Do I need to reset the idle RPM and potentially mixture following the clean?

Thanks

 

 

 

 

 

 

 

 

 

 

 

Edited October 26, 2021 by Sidebp

[Lesworth]

You should set the idle speed. There is a procedure where you isolate the ICV (I think you bridge two terminals in a relay socket in the engine bay somewhere from memory). You need to take the ICV out of the equation when you set the idle speed, effectively setting the idle speed in the centre of the adjustment range of the ICV. May have got that slightly wrong as its been 12 years since I had a 3.2.

[Sidebp]

Will give that a go. Just got the multimeter out again and definetely have 12.4v one side and 200v the other (not sure if this is even possible). 

 

I also checked resistance, I get a reading of 0 on the side with 12.4v and open loop (OL) on the other. Given the valve isn't buzzing I still have a suspicion that there may be a break some where?

[Sidebp]

Tried a couple of other things:

- Disconnecting the ICV and starting the engine and surging continues

- Tried bypassing valve and setting idle RPM and screw adjustment has no effect

- Testing the resistance on the valve and all pin combinations have a resistance of sub 10ohms (not the suggested 20/40 per the Bentley manual)

Therefore my theory is that the ICV is duff and stuck in a set position (hence unplugging makes no difference) and it's not buzzing when powered on.

Think it's time to try a replacement.

 

 

 

 

[Rustybum]

23 minutes ago, Sidebp said:

Tried a couple of other things:

- Disconnecting the ICV and starting the engine and surging continues

- Tried bypassing valve and setting idle RPM and screw adjustment has no effect

- Testing the resistance on the valve and all pin combinations have a resistance of sub 10ohms (not the suggested 20/40 per the Bentley manual)

Therefore my theory is that the ICV is duff and stuck in a set position (hence unplugging makes no difference) and it's not buzzing when powered on.

Think it's time to try a replacement.

 

 

 

 

I’ve been following your post with interest.

I have, occasionally, a bouncing idle from cold.

I checked all my vac pipes and they looked ok.

So I cleaned out the ICV and it seemed ok for a while. But then the bouncing returned.

So I bought a new ICV. Fitted it and the tick over increased by about 150 rpm.

And the bouncing idle came back.

I’m thinking it could be the cylinder head temp sensor. Which is causing it to over fuel when cold.

I haven’t tried resetting the idle yet.

I just thought I’d mention this before you go shelling out for a new ICV.

Regards

Russ

[Sidebp]

Thanks.

Unfortunately my issue is not temperature dependent and only started after I cleaned the valve (its a 1k rpm pulse every 4-5seconds). Most concerning or potentially leading is that the valve is not vibrating/humming when powered on like it used to.

Does anyone have experience of the Lowe Bosch replacement ICV? Appreciate a genuine part is probably better but it's 4x the price and pretty much every one I can find online is out of stock. There are a couple of used ones on eBay but not sure they look much better than mine, certainly not to spend over £100 on.

 

 

Edited October 27, 2021 by Sidebp

[Sidebp]

Should've added before now as title could be misleading.

My car is not only surging at idle it is pulling when driving even with no throttle input (another reason I think it might be jammed open) 

[longman]

Have you done this like I posted in your other thread?

 

 

[Sidebp]

Hi,

Yes I did, jumpered port and turned screw and there was no change in RPM at all so I was either doing something wrong or something else was overriding

[Sidebp]

Fitted replacement valve and idle now rock solid. 

To close out this thread and hopefully help anyone else who stumbles on a similar issue, here is the valve I ordered:

https://www.ebay.co.uk/itm/Porsche-911-Idle-Regulator-1984-1994-Porsche-ers-0280140501-/114765716328?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l6249&mkrid=707-127634-2357-0

Cost £62.53 delivered and took circa 5 working days, tracked delivery from Germany.

 

 

[ChesterJLampwick]

I don’t know if these valves can gum up inside when the car isn’t used much, but when I bought my 3.2 it revved up and down like a motorbike, by itself, after a cold start.

Research on here pointed me in the direction of the ICV, but as I used Iris, as a daily driver at the time I bought her, the problem just went away by itself. If only they all did that.

[proporsche]

do you have a A/C on your 911? if yes let me know i`ll tell  you a trick

 

Ivan

[Sidebp]

Looks like I spoke too soon. Took the car out today and it was fine initially but now it's surging again 🙈 

Not sure if it gives any clues but in the throttle closed position the car pulls/accelerates/creeps, the only way I can control speed is to keep changing up or gently apply brakes.

Edited November 7, 2021 by Sidebp

[proporsche]

ok i`ll try again ...do you have an A/c???

[Sidebp]

Hi, Unfortunately not.

[proporsche]

ok your problem sound to me like you fuel mix is out of adjustment ..When was the last time you had that done or checked?

 

Ivan

[Sidebp]

I did wonder that but wasn't sure on the symptoms.

I've only had the car since August so not sure when it might have been adjusted, might take it to garage to see if they can check it as next step.

Thanks

[Sidebp]

Left the car to cool overnight, started it this morning and there is no surging (suspect as it warms it will return). As it got up to temperature the idle was slowly increasing (with no bounce)

[PorscheApostle]

Surging is a classic too rich setup. Your idle valve operates at 50hz and is trying to maintain the idle so it adjust accordingly. From cold CHT (An NCT sensor from memory ), the DME enriches the mix and advances . If the that is out of spec it can mess with the mixtures. It is also important to check that your throttle plate is adjusted correctly, your idle micro switch is working and your tps is adjusted . Check your linkages too to make sure there is the necessary lost motion to the throttle plate. Otherwise the DME doesn't know it's on idle mix and ignition. If you get all the components working first , then set the idle iaw with the thread above , you can the adjust the AFM for enrichment. I'd also check your fuel pressure regulator is delivering the correct fuel pressure otherwise the delivery rate of the injectors will be wrong . It relies on vacuum to pull fuel pressure at idle when the throttle is closed. 3.2 Carreras have non sequentially fuel injection that's why they also have a damper fitted to the fuel rail for high duty cycles. 

DBS

[R2D2]

DBS has listed the main culprits. Make sure you hear a "click" as soon as you open the throttle manually by hand. The click is the sound made by the idle position switch releasing. If this idle position switch is out of adjustment/ bust then the poor little car brain get confused. Check this happening when engine hot as well as cold. Check all the hose clamps and little hoses from the back of the throttle body to the fuel pressure regulators are snug.

Another related issue could be a worn track within the Air Flow Meter (AFM). Within the AFM is a little stylus that "wipes" across a copper track (i.e. a variable resistor) which is driven by the amount of air drawn into the engine. This reading tells the computer ECU how air is coming in and therefore how much fuel to bung into the mix. Something like that anyway. The track wears out usually around the area where it sits during idle / low revs. Good news is there is DIY £0 fix which is detailed within clark's garage 944 website (944's use the same type of AFM).

[Sidebp]

Still battling with this issue, new observations:

- It's not temperature dependent

- Adjusting idle screw makes no difference

- Idle position switch has been tested and working ok

- TPS is working fine (disconnecting results in an increase in RPM)

I've booked it into a garage but soonest I can get an appointment is mid Jan. Given all I did was change the valve and adjusting idle screw makes no difference to running I am beginning to wonder if this would indicate that I have introduced a vacuum leak after the ICV (possibly I disturbed something when I removed the valve)

 

 

 

 

 

Edited November 27, 2021 by Sidebp

[apesman]

This series might be of interest..

 

[Sidebp]

Thanks - watched those, good series.

[jellyfishfields]

I really like their videos, she just gets stuck in and thinks it through as she goes. She also had a lot of idling issues.

My car suddenly decided it didn't want to idle propely the last time I drove it. Turned out to be a simple fix on mine, just to adjust the idle speed a little, but I see you've tried that already.

 

 

[Sidebp]

Yep, starting to think I might need to fly the car over there. 🤣

The issue I'm having is that every garage I've spoken to is concluding I need a new ECU, new AFM etc despite me explaining all I did was put on a new ICV. Given idle adjustments seem to make zero difference (can't even get it to stall), I sense I have a vac leak somewhere.