Peugeot 405 2.0 auto won't idle

Austria Wild

Austria Wild

Member
Fellow Frogger
Joined
Jan 11, 2019
Messages
102
Location
A Parallel Universe near England


Well, the dreaded stalling bug has hit me, sadly.
The car is very well maintained and worked beautifully. Now it won't tick over, it just stalls.
Otherwise it's running perfectly fine, smooth, no power loss, etc.

Since I couldn't find anything wrong with the vacuum pipes, especially the one to the MAP sensor, I changed the Stepper Motor/Idle Air Control Valve. This actually cured the problem for an afternoon, now the issue is back.

Here is what has been done so far:

- Thoroughly diagnosed vacuum pipes

- Took Throttle body out and cleaned it thoroughly

- Replaced Stepper Motor/IAV

- Disconnected the battery while waiting for the spare, i.e. several days, which should have reset everything


I admit that the stepper motor I ordered was the cheapest one and it has no manufacturer markings.
I know it is not uncommon for this Chinese rubbish to fail instantly.

But before I condemn an entire people, is there a way to actually test those for functionality?

Does anyone by any chance know what else I could check that might be a possible culprit?
 
Just put 12 V on the steppa motor and see it close/open. If it does, check if there is power to the steppa motor by back probing. Normal alternator output at idle?
Others will know what else to check.
 
Standard fix for the original assuming OK electrically is to wash out with petrol and then spray silicone lubricating spray into it.
 
Does the stepper merely open/close, or does it adjust for cold start/warm up, gear engaged, aircon off/on, etc?
There are four pins - which one is what?

Are there any other components worth checking in this context?
 
If it is anything like on the Renault (probably is) when i put 12 V on it just does the full movement. On second thought, it is probably safer to go for a lower voltage like 5 V. When it is working the ECM opens/closes to the degree required to maintain idle.
I think the Renault had only 3 pins. Maybe the Pug one has an extra earth???
 
A vacuum leak can mess up idling, particularly as you have removed part of the induction system. You can test the induction with LPG.
 
It's gradual not just on off. That's how it maintains idle at a specific RPM. The air circuit controlled by the valve (which is controlled by the ECU) bypasses the throttle butterfly and varies according to load etc to maintain the idle RPM at the set level. The finely adjusted air bypassing the throttle causes the AFM or MAP feedback to allow more/less fuel and therefore, more/less RPM.
 
Stuey said:
It's gradual not just on off. That's how it maintains idle at a specific RPM. The air circuit controlled by the valve (which is controlled by the ECU) bypasses the throttle butterfly and varies according to load etc to maintain the idle RPM at the set level. The finely adjusted air bypassing the throttle causes the AFM or MAP feedback to allow more/less fuel and therefore, more/less RPM.
Click to expand...
All the EFI cars I've messed around with add air to gain revs, and match fuel to keep stoichiometric or whatever is the desired fuel map modification for that temp.

I can't remember any of them adding or subtracting fuel to any noticeable amount to vary revs.

Anyway, I know the pain of not being able to get a stable idle.

My last fuego had a few too many mods , and the damn PCM Idle valves just never seemed to work.

In the end I simply plumbed an old heater valve between the the Plenum and the air cleaner and connected it to a choke cable, controlling the revs by hand.
So simple.

Jo
 
I got what you mean. The steppa motor opens/closes to the degree required to maintain idle speed.
 
This is from a R19. Putting 12V on the outside pins opens the air passage and reversing the V closes them fully. Obviously, a reduced voltage or the middle pin? would control the degree of opening. The fact that it opens and closes means it's not stuffed - in fact i know it isn't.
Why do i have it? Because a fuel injection 'specialist' told my that the flaring idle was due to a faulty steppa motor :( - it was due to a faulty alternator.
BTW, if anybody wants/needs it you can have it for free. I'll be chucking it soon.
 

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Yep, the ECU varies the voltage (or via PCM?) to open it variably. In the 206 you can actually see it constantly moving in and out by looking down the throat of the throttle body while the car's running because it's a cone shaped piston on the end of the stepper motor shaft (a solenoid) which blocks a hole in the throttle casting.
 
Check for cracks in the housing between the inlet manifold and the air flow meter ,the operation of the throttle position switch and ,that the flap in the air flow meter is operating freely and the resistance track under the top cover isnt cracked or damaged ,theres a post on here somewhere about adjusting the contact arm to compensate for wear over the years ,pugs
 
I think I failed miserably to describe the fault.

The car is stalling instead of ticking over.
Apart from that, it is running perfectly fine, there is no power loss, nothing erratic, the cruise control works as it should, no hesitation, etc, nothing. The fuel consumption is normal.

It's only that one thing - no idle. And this is completely consistent, not intermittent, not erratic. Just none.

After I changed the stepper motor, the problem was cured completely. The car behaved like it always did.
Then, after a day or so, the fault was back.
Since I think a life span of one day is rather on the short side for even a cheap Chinese component, I was thinking that there might be something that destroys my stepper motors all of a sudden.
Could this be even theoretically possible?
Is there any overload protection apart from what the silicone idiot tells it?
 
What is the minimum revs the motor will run at before stalling when the idle is controlled by hand, holding the main butterfly open? (2 person operation probably).

Is there a gap between the inlet housing and the main butterfly when it is in its fully closed position (Motor not running)?

???
 
Since the rev counter only starts at 500 rpm it's impossible to tell what the stalling rpm is.
It's impossible to see whether there is a gap between the inlet housing and the main butterfly when it is in its fully closed position, but the factory preset has not been touched.
 
Hi all. Have never played with what ails Austria Wild, but from an electrical fault finding point of view, it follows that pursuant to the 1 day of working well that you now have 2 stuffed stepper motors which can easily be tested to prove their worth. And, if neither or only the older 1 is unserviceable then the problem is elsewhere in the wiring or switching. If the older stepper still operates and the new 1 is also good then the most likely scenario is that in fitting the new, but cheap, unit something was disturbed which enabled the good day before resorting to being an issue. Checking, cleaning and soldering of all wiring involved would be a good start. It is quite possible to have a reading of 12V at a connection, but will it stay at 12V when a load, such as stepper motor, is applied ? Love my 405 SRDTs, but they are ageing and I have had to re-route starter motor wiring in order to bypass a failed connection point.
 
Problem fixed.

A piece of advice I bet you all always wanted to learn: Make sure the connector of your MAP sensor is actually connected to your MAP sensor and not fallen off dangling on your valance.

However, the old stepper motor has actually had it and the new one was required.
When checking the connector of the MAP sensor, I must have failed to push it all the way home, so it fell off after a few miles.

I should not work on cars. Why do you guys let me?
 
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