Technical Idle hunting?

[dac69er]

When my car gets up to temperature, the idle hunts in a constant cycle.

It is steady @ just under 1000rpm, then after about 5 seconds the rpm drops to about 600rpm for a second and then comes back up to just under 1000rpm again. It keeps cycling like this.

I have changed the following to no effect:
Lambda sensor
TPS
Fuel filter
Map sensor
ICV

I have checked sensor readings using iaw scan. Reset the idle control and mixture settings off the parameter screen. No difference.

This just suddenly came out of nowhere? It is perfectly fine starting from cold, it's only an issue once up to temp.

Any ideas? The only thing I am wondering is could it be the cranks sensor? No fault codes, but it could be on its way out perhaps????

The only other issue of note I have had recently is a couple of occasions where the immobiliser wouldn't allow me to start. I had to wait a few minutes and then it was ok, it has been ok recently though.

 

[dac69er]

Changed the cranks sensor anyway and double checked the fuel pressure was ok.
Also undone and re-tightened all the engine ground points.

Still the same issue

Any other suggestions?

 

[loucifer]

Whenever I tried doing an idle reset through IawScan2, I didn't manage to make it work. I have found that the best way to do it is the Haynes manual way. Let the car reach temperature, let the fan kick in twice, immediately turn of the engine and take of the negative pole (or the power to the ecu), wait for 45 seconds, reconnect battery (or connect power to the ecu), start engine and let it idle for at least two minutes.

Also, are the readings on iaw scan normal when the problem appears? Is the rpm reading going down the only thing that happens during the scan? Throttle at Min, Lambda in Closed Loop, Stepper autocalibration enabled?

 

[dac69er]

Whenever I tried doing an idle reset through IawScan2, I didn't manage to make it work. I have found that the best way to do it is the Haynes manual way. Let the car reach temperature, let the fan kick in twice, immediately turn of the engine and take of the negative pole (or the power to the ecu), wait for 45 seconds, reconnect battery (or connect power to the ecu), start engine and let it idle for at least two minutes.

Also, are the readings on iaw scan normal when the problem appears? Is the rpm reading going down the only thing that happens during the scan? Throttle at Min, Lambda in Closed Loop, Stepper autocalibration enabled?

Thanks, I will give that a go and see if that works, it takes a while to get it fully up to temp when it is so cold out!

It doesn't do it all the time, but probably about 90% of the time.
I've not had time to check it in detail whilst running and warmed up on iaw scan, so will try that too.

 

[dac69er]

Disconnected battery for a few minutes after getting up to temp. Still no better. Arguably worse as it now stalls after the revs drop a few times

Tried monitoring when it had the issue, but I had to stop the engine to get iaw scan to connect and then it ran fine after restarting.

I took pics of the readings in case anyone can see anything obvious. please see attached. still no error codes

 

[dac69er]

Changed the injector today. Still no better.......

 

[loucifer]

Disconnected battery for a few minutes after getting up to temp. Still no better. Arguably worse as it now stalls after the revs drop a few times

Tried monitoring when it had the issue, but I had to stop the engine to get iaw scan to connect and then it ran fine after restarting.

I took pics of the readings in case anyone can see anything obvious. please see attached. still no error codes

The obvious difference is that in my Spi Seicento sporting, IAWscan2 shows both Mixture AutoCalibration ENABLED and Stepper AutoCalibration ENABLED are YES. If I remember correctly, you can toggle both On or Off in the IAWscan parameter tab. To give further information, I have also an 899 cc Cinquecento that I can't toggle Stepper AutoCalibration ENABLED to YES and that Cinquecento has a problem with the rpm dropping when it is up to temperature (but in my case it doesn't happen when idling and the Lambda reading drops also)

 

[dac69er]

Interesting. I will try and toggle these on whilst running and see if that helps.
I did try setting these to on before, but didn't check to see if it actually did anything on those parameter screens I posted up, I will take a look.

Thanks

 

[loucifer]

Interesting. I will try and toggle these on whilst running and see if that helps.
I did try setting these to on before, but didn't check to see if it actually did anything on those parameter screens I posted up, I will take a look.

Thanks

You can toggle them to showing YES in the Adjustments tab (at least that is the case in my Seicento 16F Spi ECU) Do it one by one without starting the engine. Connect to IAWScan but don't start the engine. Check in the Parameters tab that Mixture AutoCalibration and Stepper AutoCalibration are indeed showing NO. If so go to the Adjustments tab and choose Toggle fuel trim autocalibration and then hit execute. It should show Passed (if i remember correctly) as result. Go to the Parameters tab and check if anything changed. If it has changed to YES, Disconnect and repeat the procedure for the idle stepper autocalibration. Both adjustments also reset the values so prepare for the ECU to relearn. Drive it normally for some time.

 

[dac69er]

I didn't get the chance to plug the laptop in today as it was raining constantly. However, I did try unplugging the idle control valve and it ran fine. As soon as I plugged it back in, the idle dropping off returned.

Something is obviously telling the idle control valve to cycle like it does.

Hopefully it will be dry tomorrow and I can investigate further......

 

[dac69er]

Had a look this evening.

Reset the mixture and idle and this bought on the 'yes' enabled messages on the parameter screen.

Started the car up and it seemed ok. Let it idle for a while and settle down. Took it for a drive and the idle dipped a bit when coming to a stop so I have opened up the throttle stop just a tad so it doesn't drop anymore.

Will see how it goes, fingers crossed it will be ok now!!!

 

[dac69er]

It seems to be sorted out now, fingers crossed.

Just need to play with the throttle closed position so idle doesn't drop when coming to a stop.

Thanks all for your assistance

 

[dac69er]

Ok, new problem now.

Hunting is no longer an issue, but I now get random stalling when slowing down and I put the clutch in to come to a stop or change gear.

Tends to be once the car has had been driven for a minute or 2 so has a little bit of heat in it. If completely cold or up to temp, it seems to be ok.

Any ideas?

 

[Prawny12009]

Check not only for air leaks but for blockage in the vac lines on the throttle body.

If the passage are blocked your idle will suffer, also double check your lines are on the right stubs.

The holes are different diameters through the throttle body casting.

 

[dac69er]

None of the pipes have been moved for years, so nothing will be in the wrong position.

Not a bad idea to check for blockages though.

I have a snapped suspension spring so the car is off the road for a bit whilst I get that done.

Will get that sorted and then get back to sorting the idle issues