idle control valve problems C20XE

[whitie]

After going through 3 supposedly OK second hand idle control valves on my c20xe
and then a £35 reconditioned ebay special (that did lower the idle for a month)
I'm finally running out of options before handing £200 over to my local vauxhall
parts dept for a brand new valve.
I have even smashed two open to see if it's a simple electrical fix to cure the 3000rpm idle,
but they wont be seeing service again....
Has anyone a cheaper reliable fix to this issue or will I just have to fork out the reddies
to the stealers?
cheers for any help

[show n shine]

leave it soaking in petroleum over night (the mechanical part that is). then squirt a tad of wd40 or a drop of oil. reconnect and take it from there.

[Nova_Tek]

a good few blasts of Carb cleaner, a good shake, a few good squirts of WD40 and then a couple drops of clean oil does the trick.

[Vinci]

I don't think you have an ICV problem mate, it could be, but high idling can have various other reasons. These Bosch ICV units are built like a tank, if you have three on a row failing on you I'd get a lottery ticket immediately!

First of all you need to confirm whether the ICV is sent open electrically, this can be done by measuring voltage on the connector. If it does get voltage there is a possibility your throttle valve switch/potentiometer is bad or the wiring towards it, making the ECU send it open at random. If it doesn't get voltage it should stay nicely closed and the rpm should not be able to rise unless there is an air leak.

To find an air leak you often get the advise to spray brake cleaner here and there, but air leaks can be due to a torn hose or failing gasket and the gap may be closed fine most of the time. What I found worked quite well is taking the SFI box off and just blow through the ICV hose. This should give a lot of air resistance, and when you manually open up the throttle valve it should blow freely. Any gaps will be opened up by the pressure of blowing and you'll hear the air hissing from the leak.

With this method I have diagnosed my first throttly body was tinkered with, some numb had grinded a little bit off, probably due to very low RPM and it was leaking like crap. Made me crazy trying to get the RPM under 1250!!

[Vinci]

P.S. WD40 is the most overrated crap on earth. It does smell nice though.

Why?

Okay it does do a fairly good job to make a nut go smoothly over a rusted bolt, but to get a rusted nut loose there are already MUCH better products (Loctite Freeze Release for example) For lubrication you can enjoy the effects for a couple of hours, maybe days, but WD40 evaporates. Take a good teflon spray of industrial quality, like Interflon and you'll be amazed!!

[Joker]

WD40 Smells like chocolate when ya first spray it lol it does up my nose anyway lmao.

[whitie]

Thanks for the cleaning tips but I went through that with the first few to no avail.
Some interesting ideas there Vinci, I did check my ICV, airmass, TPS and lambda with a voltmeter according to
auto data when I first relocated the engine; all figures suggested things were fine. I even left one ICV
plumbed into the inlet while plugging in another to the loom to see if they actually did anything,
and all behaved similarly with the valve fluttering open and almost closed very quickly.
From what I have read about ICVs online I was under the impression they were a common problem,
and last time I ran the engine (from cold) I tried a suggestion of disconnecting the electrical connector to see if the
revs changed as it runs at a "safe" predetermined level; they dropped from 3k to 2k....
Next thing I was going to try was running the engine up to temp (coolant needs bleeding so two jobs in one)
and seeing if the idle drops when warm as I also read that the ICV is not used that much after warm up
(true or not I'm yet to find out).
So you say the ICV shouldn't be getting a voltage, is this with the throttle open then, as I would have
though a voltage would be vital for the valve to balance the idle? I cant recall what measurements I
observed last time I tried back pining the connector as it was a fair while ago.
While testing the TPS I noticed there were basically 3 switching states: closed throttle/open throttle/full throttle.
Does the ICV basically switch off (or meant to) once the closed throttle switch is not engaged then?
Thanks for the help, just want this engine to run properly like it did when I first bought it!

[Vinci]

The ICV ONLY will be regulating when the TPS is at idling mode, and it has only two modes, idling and throttle open, not full open (I've opened one up and the schematic is also clear about this) If it won't click in to diling mode the ECU will enter a sort of mode thinking you are applying throttle at some unknown level.... Mine ran at several RPM rates and often going from 1500 and rising towards 3000 and up without lowering again.

It is important you don't only hear it click (with Motronic 2.5!! With DIS it is a pot.....) but also disconnect the ECU plug once and beep through the pins right there to confirm you also don't have a wiring problem.

Then another thing, when you remove the air box and have a tool at hand to completely block the ICV hose (something like two sticks and a tie-wrap) you are in full control of the air distribution towards the engine. Then you can see what happens when you block the full air flow into the engine, it should go down and finally let the engine shut off. Don't do this for too long, just for a quick test because it will cause a too rich mixture and cause sooting inside the cylinders.

I have a friend who had an inlet manifold gasket with a damaged corner and it sometimes fell into place, sometimes opened. This also caused irratic RPM behaviour....

If nothing of this works I would get a spare ECU to check if it makes any difference, maybe one you can borrow....

[DarrenH]

if you get the bosch part number off the side of the barrel. take that to an independant motorfactors (most of which can deal with bosch direct) this will give you a significant saving over vauxhall dealer on brand new bosch items.

[Vinci]

if you get the bosch part number off the side of the barrel. take that to an independant motorfactors (most of which can deal with bosch direct) this will give you a significant saving over vauxhall dealer on brand new bosch items.

Good tip! Same goes for wheel bearings, the really good ones are from SKF and bare the SKF partnumber. This will save you a LOT, only you don't get the circlips with it, but these are well reusable....

[Vinci]

Actually the basic guidlines for C20XE M2.5 high idling are pretty simple:

Step1: Determine what way the engine gets more air than it should. (by the blowing method I posted above for instance)

Step 2: Squeezing the ICV hose, if it makes the engine revving very low or even shut off the high revving is due to the ICV sent open.

Step3: When step 2 applies chances are 99% the TPS isn't working/wiring is screwed/isn't properly adjusted, it should not only say 'Click'...

For as far as I know the MAF sensor, Lambda don't have anything to do with it.

Temp sensor does, but it shouldn't make the world of difference, but it can't hurt to check it out. General RPM vs. temp:
-45C => 1350 rpm
-27,25C => 1180 rpm
6,75C => 1150 rpm
60,75C en hoger => 940 rpm

So even if it thinks it is freezing minus 45 degrees Celsius it should run higher than 1350 rpm.....

[whitie]

well after 3 days working on this my second corsa my c20xe has been in, I feel completely demoralised and reaching for the tow rope to drag it to scrap!
The only tiny hope I'm clinging to is something I did find out last time I was testing
the TPS; the points at which the switch goes from open circuit to 0 resistance
over pin 1 & 2 (closed throttle) and from open circuit to 0 resistance on pin 2 & 3
The opposite end of travel so fully open) are beyond that at which I can set the TPS
with the small screws in the elongated holes.
Is this some kind of twisted normality or is something very wrong?
On the basis of the above logic; this would mean that the ECU is always seeing open
throttle? And so similar to Vinci's 1500-3000 rpm.
After jump starting the engine (battery is knackard now!) the revs would sore to 3k,
with ICV disconected this would be 2k, and with ICV hose to SFI box clamped,
then this would be 1200rpm..... After a while of running to see if a warm engine would
change things, the engine would start to stutter and die.
After going through all the above again then I was able to release the clamp on the
ICV hose once the engine started to stutter, this then allowed the engine to idle
between 900 and 1100 with the occasional splutter from the exhaust and black smoke.
I then read off the EML flashing fault codes;
13 - O2 sensor wiring open circuit
44 - O2 sensor mixture weak
48 - Battery supply voltage low.... obviously
66 - Mixture adjustment resistor - voltage high
73 - Mass airflow- voltage low

After leaving the battery off for half an hour while I checked the butterflies were not set open by the throttle cable and I even made a new throttle body to inlet manifold gasket to see if that helped, I started the engine and it shot
straight up to 3k, not wishing to annoy the neighbours any further on a Sunday
I decided to go for the first test drive ( car has not moved more then 6 inches for
a year), as soon as I came off the clutch and gently accelerated the car kangeroo'd
down the street at around 1k revs unless I put the clutch in and high revs would
resume. The engine then cut out whilst kangerooing and of course the battery was flat.
Frustration is not a good enough word, I prefer rage to describe my feelings for this car!
So my question basically revolves around the TPS; is there a reason I cant set it
far enough to get it to switch from open throttle?
Does it make sense that it is causeing those fault codes,
and what is the mixture adjuster resistor(ECM)?
Any help greatfully recieved before I drive off to the scrappy!

[gadgetman]

try parts_dome on ebay - I got a new one from there £29, it hasn't broken yet.

Idle Air Control Valve Astra Vectra Omega Calibra | eBay

[Vinci]

Dude, are you 100% certain the adjustment screw on the spring set on the cable pulling side of the throttle body isn't turned to keep the throttle always slightly open?? This would also prevent the axle of the butterflies to turn back far enough for the TPS to click. I've had this on one of the throttle bodies I tested on my engine and it made me just as mad, even opened up the TPS and bent the switch, which made it run fairly well for a while. But after I got it fixed by swapping for a complete throttle body that worked fine I went back to look at the differences and found this out. Now it is doing a fantastic job on a friends engine!

I've pointed it out here:

[DarrenH]

assuming you have a distributor c20xe. at rest the throttle position switch should be closed circuit (no resistance)

then the other pole should be open circuit until about three quarters wide open throttle then go closed circuit

i've done this myself today, trying to diagnose a running issue.

a guy on astra-mk2 had the same issues as you (high idling) when his TPS failed on the first stage

[Vinci]

Another thing you could do is just unplug the multi plug of the TPS and just short it by hand, or fully unbolt the TPS and turn it by hand until you are 100% certain it is completely in idling position.

If this isn't working right I bet you a 100% it's going to idle very high!!

[Vinci]

assuming you have a distributor c20xe. at rest the throttle position switch should be open circuit on all poles (infinite resistance) it should click (audibly) as soon as the throttle moves and go closed circuit (no resistance)

then the other pole should be open circuit until about three quarters wide open throttle then go closed circuit

i've done this myself today to test it trying to diagnose a running issue.

a guy on astra-mk2 had the same issues as you (high idling) when his TPS failed on the first stage

That's not intirely right...

[DarrenH]

so either i have got it back to front while recollecting, or my tps is actually fcked lmao

[DarrenH]

so either i have got it back to front while recollecting

that one. i've edited my reply so not to confuse in future, thanks for the quote vinci

[whitie]

Cheers for pointing out the adjustable throttle stop but that was adjusted well out of the way about 2 years ago.
My latest workings have been;
Fitted a new TB to intlet gasket from vauxhall £1.27 (bargain!) and ordered a new TPS for £34 delivered.
TPS was out of stock for a week so when I fitted the gasket I removed the original TPS and filed out
the securing bracket the screw goes through so I could reach the closed throttle switch point when
TPS was re-attached.
I also put a switchable earth wire to pin 20 of the ECU so I could try ruling out the Lambda probe.
After starting the engine with everything connected and TPS now reading the correct 'closed'
position of the TB, the revs sat at 1500 pretty steadily with no splutters or smoke from the exhaust.
As the coolant temp rose the revs did slowly increase to 1800, so I thought I'd try the lambda'less function
and have a play with the brass screw on the AFM. Revs dropped to 1600 but changing the resistance
with the brass screw didn't seem to do much so I disconnected the earth and reconnected the lambda
plug, at which point the revs decided to hunt between 1000 and 2000. So I then clamped off the ICV
to SFI box hose, this stopped the hunting and dropped the revs to 1100....
What is worrying is that the engine still revs slightly too high with the throttle fully closed and the
ICV intake clammped off!
So I must have an air leak? I narrowed it down to; inlet manifold gasket,
2 x crankcase breather hoses,
vac pipe for fuel reg,
brake servo vac pipe,
or a crack??????
Not very narrow but hey, closer than the week before!
Any more words of wisdom? It's getting desperately close to going as spares/repairs!

[whitie]

try parts_dome on ebay - I got a new one from there £29, it hasn't broken yet.

Idle Air Control Valve Astra Vectra Omega Calibra | eBay

Cheers, the last one I bought was from Ebay for about £35 and was reconditioned, it did seem to improve things so I'll keep this in mind.

[Astra Dan]

Try blocking the inlet to the brake servo?

[whitie]

assuming you have a distributor c20xe. at rest the throttle position switch should be closed circuit (no resistance)

then the other pole should be open circuit until about three quarters wide open throttle then go closed circuit

i've done this myself today, trying to diagnose a running issue.

a guy on astra-mk2 had the same issues as you (high idling) when his TPS failed on the first stage

Yep, its a dizzy c20xe sorry.
Well new TPS has arrived so I hope this improves things again, but I presume
I must have an air leak as the original TPS still switches OK when in position...

Thanks for the autodata page above Vinci, that's what I had a few years ago and worked off.
As for the testing of the inlet system with blowing air, I'm afraid I don't have access
to a compressor, is there another way I have stupidly overlooked?
Also, wouldn't the valves need to be shut, so engine timed up to mark?

[whitie]

Try blocking the inlet to the brake servo?

Would you suggest using a bung of sorts as the plastic tubing seems quite fragile to clamp?
Or is clamping fine?

[Vinci]

Make as plate to close the throttle body completely, even wood is OK, place it with some sealant and then blow on the icv hose. It should hiss somewhere...

If not then try some soap and water and see if there are any bubbles arising somewhere when you blow on the hose.... The air can't go anywhere when it is all sealed and if it can there obviously is a leak. The engine should really stall and shut off when the IVC hose is clamped!

Also it should REALLY not be necessary to file out the adjustment holes on the TPS....