156 TS ('99) Stalling when coming to a stop

martym00se72 · February 06, 2019, 04:56:53 PM

Hi Folks,
My 156 TS manual has developed a bit of a funky behaviour of late. It had an uneven idle and had started to drop revs and stall when coming to a stop or turning a corner at low speed (like pulling into my driveway). If I blip the throttle as I come to a stop then it keeps its head and will just idle as expected when I come to a stop. If I don't blip the throttle it will just die.

I found a loose clip on an air hose so hoped that might be the cause but that doesn't appear to be the case, though clipping that seems to have smoothed the idle somewhat.

Any ideas on what might cause this? What I should be looking for?
Cheers
Marty

poohbah · February 06, 2019, 05:33:38 PM

It's "probably" not this - but simply for your peace of mind, check that there are no fuel leaks from fuel rail/injectors.

On the day my engine caught fire a few years ago, my V6 156 started rough idling and was uneven when coming to a stop - not terribly, just enough to notice. Unfortunately, it went up on my way home that evening (the night before it was booked in for service). The cause of fire was traced back to a leak from the fuel rail onto a hot exhaust manifold.

Citroënbender · February 06, 2019, 06:02:41 PM

Crank sensor?

bazzbazz · February 06, 2019, 07:46:22 PM

Just out of curiosity has the brake pedal feel changed in any way? Become harder maybe when this happens?

You may have a air leak in or around the Variable Inlet Manifold or the Brake Booster Vacuum Line.

martym00se72 · February 06, 2019, 11:50:11 PM

Hey Citroenbender, can you explain your thinking on the crank sensor?

Bazzbazz - brake seems unchanged. Whats the best way to check for air leaks?

Thanks guys for your thinking!

Craig_m67 · February 06, 2019, 11:59:43 PM

I don't think it's the crank sensor. When this starts to fail intermittently it kills the engine stone dead (will crank normally but won't catch) until the engine is cool/cold again. Then it works, until hot.. when it kills the thing dead again. Eventually it just fails and you replace it (under the starter motor, 6mm bolt head, $10./ part from Bosch I think)

I think Bazz is on the right track with air leaks
What's the idle like when you turn the aircon compressor on and off?

Is the battery and all connections tight...

Citroënbender · February 07, 2019, 05:42:01 AM

As Bazz often points out, it's the loss of magnetism (degaussing) that usually causes loss of sensor output. This is not a sudden drop but a progressive failure, being noticed only when the threshold of non-functionality is crossed.

In a magnetically weak state, the sensor may just produce a useful signal at higher engine speed; slowing of the crank reduces the acuity and you have a stalling situation.

bazzbazz · February 07, 2019, 05:32:45 PM

The loss of Gauss in the crank sensor is due to heat. Magnets don't like heat, and over time the magnet in the sensor depletes to the point that when it gets hot it looses whats left of the magnetic field and stops building a signal, engine shuts off.

It won't be the Crank sensor, as Marty mentions, if he blips the throttle right just before it stalls it will keep going, that does not sound like a Crank Sensor failure.

May I suggest checking the air intake pipe from the MAF Sensor to the Throttle Body, especially the rubber concertina section. Also check the Two Crank Case Breather hoses, one goes from the side of the Camshaft Cover to the inlet pipe. The other goes from the back of the cam cover to just behind the throttle body.

Next, check the back seam of the Plastic Variable Intake Manifold. It is made in two halves joined top to bottom and the is a seam along the back that can sometimes crack/split. Remove the intake piping & throttle body and have a look with a mirror, or get under the car and have a look up and use mirror again.

martym00se72 · February 08, 2019, 10:17:57 AM

Awesome Bazz - thanks for the explanation on the crank sensor and based on your description, I agree, it does not sound like the crank sensor, especially as the car will exhibit the described behaviour even when dead cold so the magnet shouldn't be degraded by heat at that point.

Thanks for the advice of where to look, I hope to get a chance to check it out this weekend now that I have some idea of what I am looking for!

Have a great weekend guys!!

Citroënbender · February 12, 2019, 01:55:52 PM

Any progress on diagnosis/repair?

martym00se72 · February 12, 2019, 02:18:12 PM

Sadly, no. I had family commitments on Saturday and on Sunday I just 'had' to take the GTV6 out for a spin as it has been close on 2 months since properly stretching her legs. Good for the soul (belting through the freeway tunnel in 3rd flat knacker with the windows down has a way of putting a grin on your face!) but not so good for the 156...

Citroënbender · February 12, 2019, 04:35:40 PM

Ah yes, totally understand!

Mick A · February 14, 2019, 12:16:40 AM

Quote from: martym00se72 on February 06, 2019, 04:56:53 PM
Hi Folks,
My 156 TS manual has developed a bit of a funky behaviour of late. It had an uneven idle and had started to drop revs and stall when coming to a stop or turning a corner at low speed (like pulling into my driveway). If I blip the throttle as I come to a stop then it keeps its head and will just idle as expected when I come to a stop. If I don't blip the throttle it will just die.

I found a loose clip on an air hose so hoped that might be the cause but that doesn't appear to be the case, though clipping that seems to have smoothed the idle somewhat.

Any ideas on what might cause this? What I should be looking for?
Cheers
Marty

Hi Marty,

From what you've described, I think that you will need to do a "Throttle Adaptation Reset". This requires a scan tool. We have an old Snap On "Brick" scanner that we use to do this, as I don't think MultiECUscan has this function from memory..

The test lets the ECU re-learn the closed/rest position of the throttle body butterfly.

Cheers

-Mick