CF2 2.0TS High Idle - Not the usual Fix - Alfa Romeo Forum
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(Post Link) post #1 of 14 Old 21-06-17 Thread Starter
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CF2 2.0TS High Idle - Not the usual Fix

Hi all,

I am having some trouble with the CF2 2.0TS in my 916 GTV. It keeps idling up around the 1500 to 2000rpm mark.

A bit of background:
It is a March 2000 build car, which has the Bosch Motronic 1.5.5 ECU. It has a Throttle Cable on one side of the throttle, and the Throttle Potentiometer and Idle Stepper Motor on the other side.

I had a leaking radiator so while replacing that, I also replaced the Thermostat and as the Temp sensor broke upon removing it from the old thermostat, i replaced it with a new FACET unit.

As well as this I replaced the intake manifold with a good 2nd hand unit due to another issue. These repairs were done in the last 2 months and a few hundred miles ago, while this idle issue has only occurred in the last week or so.

So during my investigation so far I have found:

When starting cold it idles around 1200rpm, slowly drops down as the temp increases, then at a certain temperature, the idle starts to creep up from around 1050rpm to the figure of 2000rpm.

I have removed and cleaned the Throttle. No difference
I have re-adjusted the throttle cable preload/adjustment screw. No difference
I removed the throttle cable whilst the engine was running to ensure it was not binding, no difference.
I have tried the ICM "tap" trick, where you tap the Idle Control Motor with a screw driver handle, no difference.
I have removed and disassembled the ICM and cleaned it up. No difference

Using MES I have re-adapted/reset the Idle Control Motor, you can hear (and see) the throttle moving when it does this. Readings After adjustment:

@ Throttle closed, i have:
Absolute Min Throttle Pos: 31.2 Degrees
Current Throttle Pos: 33.0 Degrees
Delta Throttle Pos: 2.8 Degrees

@ WOT, i have:
Absolute Min Throttle Pos: 31.2 Degrees
Current Throttle Pos: 109 Degrees
Delta Throttle Pos: 77.8 Degrees

So that says to me that the Throttle Potentiometer is working. The stepper motor moves, so I believe the ICM is working also. I also have a spare (used) Idle Stepper/Throttle Potentiometer, I have fitted this and the same fault persisted even after running a new throttle adaption. So i swapped back to my original one. None the less I feel that both units are good.

I start the engine, left running until the cooling fans have kicked in atleast once. Plugged in MES and monitored these figures

Coolant temp: approx 98 Deg C with bonnet open, sat stationary @ 2000rpm. As i have a new CTS I trust this reading.
Target Idle RPM: Approx 2000rpm
Current RPM: Approx 2000rpm +/- 100rpm variation.
Target IDLE MAF reading: 14kg
Current MAF: 25kg
Lambda Reading (Volts): Fluctuates between 760mV and 130mV with every parameter update.
Measured Battery Voltage: 13.47VDC (measured via MES, i have not verified this reading is correct yet)

If I unplug the MAF, it then idles like a dog and is very rough to rev, also takes longer for revs to settle. so I think the MAF is okay as it is better when its plugged in. Plus it does measure and that measurement varies with engine RPM.

This Lambda reading indicates that it is measuring a Lean state @130mV, so it was suggested that it is an air leak.

Armed with a can of WD40 i have sprayed around the intake, and none of these places seemed to effect the engine speed (i would expect it to bog down if there was a leak):

Intake Pipe work between the MAF and Throttle Body. No splits/tears/cracks either.
Around the plastic Intake manifold
Around the Throttle body.
Around the Brake Booster Vacuum line/feed. either ends.
Cam Cover to Intake Pipe hose
Cam Cover to intake Manifold Hose
Spraying under the intake manfiold (near the Evap Solenoid) makes no difference either.

Unplugging the Evap Solenoid makes no difference either, so it is not stuck in an "open" state and if there was a break in the hose inbetween the Evap Solenoid and the Intake, i think I would have found it with the "leak test".

So I am a bit stuck as to the cause.

MAF Okay
EVAP Solenoid isnt stuck open
TPS works
ICM works
I trust the Coolant Temp sensor
I cannot find any intake side air leaks.

But something is tricking the ECU into thinking it needs to rev to 2000rpm.

The only other thing I can think of is that if I unplug the Lambda sensor, the engine runs, and will Idle around 1500rpm, but will drift slowly down to 980rpm which I believe is the correct idle RPM. So maybe a duff Lambda sensor is causing the ECU to over fuel, which is then making a rich AFR, allowing it to rev up to 2000rpm at Idle. This would also make sense as it idles fine when cold, but as it goes from Open Loop to Closed Loop EFI, it would start reading the Lambda Sensor.

So would anyone agree that it is safe to assume that I have either:

A Cracked/Leaking exhaust (I cannot hear any Chuff or noises i would associate with an exhaust leak, nor see any signs of an exhaust leak)
or
A dead Lambda O2 sensor?

any comments/suggestions are welcomed!

TIA

Last edited by Taylor93; 21-06-17 at 14:44.
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At the end of the cam cover to manifold hose is a small plastic valve ... spring loaded and prone to several things:

1) it can get gummed up over time as oil leaves the crankcase and is sucked into the intake (part of emissions system)
2) the outer case of said valve gets brittle and the clips on the end depart for a better life and then air gets in
3) the innards are lost when you swap over the intake


Also if you have FiatEcuScan or MES as it now known (or a working copy of AlfaDiag), have you tried resetting the throttle and then the 30-second trick?
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cheers, Gary

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Had exactly this problem on my Fiat Coupe 20V VIS (just about all of them had this issue), it's got the same set up as the TS. The post from Gazza above has given you the answer, quick check to do when it is idling too high is remove the oil filler cap and see if the idle drops to the right RPM.

The fix is to remove the spring that sits on the poppet valve (see picture above) and leave it out, then put everything back together and the car will run correctly. You'll need to reset ECU and do the throttle learning as well afterwards but it's a pretty easy problem to fix.
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(Post Link) post #4 of 14 Old 26-06-17 Thread Starter
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Gents,

Thank you for showing an interest, just out of curiosity, do either of you know how this causes the higher idle?

I will have a look at it tonight. My concern is how to test it? if i open the oil filler cap, then that will let in air after the MAF at the Intake breather.

I did find that my downpipe is like swiss cheese at the moment where an exhaust clamp at the subframe has been rubbing and has left several small holes in the exhaust.

So i have a new pipe to fit, plus a new lambda sensor.

I did try to seal the exhaust system, just to prove the concept that it was an exhaust leak, but the high idle returned after a few hours of driving.


Yes i did also try the throttle/self adapt resets too.
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Also, how do you remove the breather from the intake manifold? does it clip on? does it just slide/pull off?

I damaged on intake manifold so i swapped it with a 2nd hand one from a friend, the replacement still had this breather fitted. I might pull my damaged old intake manifold apart to remove this part, then fit it to my current intake as it works.

I have all the parts so should be able to quickly swap them out tonight!

thanks again gents! it is giving me hope! haha
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It's really easy to take off, referring to the photo in Gazza's post:
  • Using a small electrical screwdriver (or similar) carefully insert it in the small recess in the top part of the breather (just by the O ring) in the photo
  • With a small bit of pressure lever the top part off the lower part (doesn't need much), the top part will come off easily.
  • Remove the PCV valve and spring from inside
  • Remove the spring
  • Clean up PCV valve (poppet)
  • Clean up hose attached to top and anything else you can get to.
  • Replace valve (poppet), do not reattach spring
  • Replace top, just needs a small bit of pressure to reattach it.

The valve is part of the Positive Crankcase Ventilation, a quick google will reveal all but basically it allows the gases that blow by the piston rings to vent in a controlled manner. It's all part of the engine wearing, I wouldn't worry unduly and get an engine rebuild though!!

If it makes you feel better I went down the same path as you, looking for leaks, putting on a new Lambda and MAF. Frustrating as a really easy issue to rectify, hopefully the fix above will sort your problem.
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(Post Link) post #7 of 14 Old 27-06-17 Thread Starter
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Right so before I replaced the PCV, I thought I would try something. I disconnected the hose at the cam cover and put a large bolt in the pipe with a jubilee clip on to make sure it was tight. Then a Nitrile glove, wrapped over a few times, jubilee cliped to the top of the cam cover. This meant that the PCV path was blocked and air tight.

Idles perfectly.

Says to me that there is too much air coming from the breather into the intake.

So i pulled the PCV off, I had a spare so i was going to fit that... i dropped the replacement spring, it went through the bonnet catch hole into the steel box section, never to be seen again!

Anyway my spare housing and o-ring seemed in better condition than the one i took off. So I cleaned it all up, reused the old poppet and spring, put it all back together.

Removed the glove and bolt, i.e. back to OE spec. And it still idles too high.

Refitting the Bolt and glove, i.e. blocking the breather, then makes the engine run correctly.

So either:

1) the spring has gone soft and is letting in too much air
2) my crank case pressure is too high.

Now regarding the 2nd option, I do tend to run with a bit more oil than i should (I check the oil when cold rather than hot to make sure that upon starting, it always has some oil) but this does mean that once warm, the oil level would be deemed "high".

Perhaps this excess oil is causing my crank to become too pressurised.

Ill drain some oil out tonight and see if that makes a difference. but for now, driving around with the 1 breather (cam cover to intake hose before the throttle body) may just get me by!

Last edited by Taylor93; 27-06-17 at 08:24.
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The fix is NOT to refit the spring when refitting the PCV poppet valve.
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Quote:
Originally Posted by wal5 View Post
The fix is NOT to refit the spring when refitting the PCV poppet valve.
Why would you Not fit the spring? Its there for a reason surely!
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Why would you Not fit the spring? Its there for a reason surely!
OK understood, I'll leave it to you.
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Quote:
Originally Posted by wal5 View Post
OK understood, I'll leave it to you.
Wal5, I didnt mean to come across snotty or blunt, I am just curios to know why it is best to remove the spring.

I do appreciate the help I am getting on here!
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Try the 90 second reset .. turn the ignition on for 90 secs but don't touch throttle, turn off for 90 secs. Now start car without touching throttle pedal and leave it to idle for a few mins .. the idle should drop after a min or so. If it doesn't you may need to reset the idle actuator with MES as this is now out of sync with the ECU. You will have to repeat the 90-sec reset. Pulling the throttle cable causes this too.

This caught me out a few years ago and I tried different throttle bodies, changed the idle actuator motor and eventually found that missing PCV valve (or at least the innards!)

And put the spring in the PCV .. it doesn't work properly without it. The spring pushes the valve closed.

The reason it ides high is as the crankcase pressure increases as you rev higher, the valve opens and lets the crankcases directly into the intake rather than passing it through the throttle butterfly. The other hose is for low speed crank pressure which goes to the inlet hose before the throttle body (and gums it up!)

It's part of the emissions system ..
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Quote:
Originally Posted by gazza82 View Post
Try the 90 second reset .. turn the ignition on for 90 secs but don't touch throttle, turn off for 90 secs. Now start car without touching throttle pedal and leave it to idle for a few mins .. the idle should drop after a min or so. If it doesn't you may need to reset the idle actuator with MES as this is now out of sync with the ECU. You will have to repeat the 90-sec reset. Pulling the throttle cable causes this too.

This caught me out a few years ago and I tried different throttle bodies, changed the idle actuator motor and eventually found that missing PCV valve (or at least the innards!)

And put the spring in the PCV .. it doesn't work properly without it. The spring pushes the valve closed.

The reason it ides high is as the crankcase pressure increases as you rev higher, the valve opens and lets the crankcases directly into the intake rather than passing it through the throttle butterfly. The other hose is for low speed crank pressure which goes to the inlet hose before the throttle body (and gums it up!)

It's part of the emissions system ..
Gazza That was my understanding too, after reading your page about the idle saga, and finding the poppet had been completely removed and had rough running, i was very surprised when Wal said to remove the spring, and without that it would inevitably end up in a situation where the poppet gets stuck and then shows similar symptoms as to having no poppet at all. Without the spring there is no control over its position.

Ill have another crack at it tonight.
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any news on that? Did you manage to have it fixed?
My 2.0 TS suffers too at the moment
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