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Discussion Starter #1 (Edited)
Hi everyone,

My car has a weird idling problem which is difficult to diagnose.

The engine itself has no problem (XU7JP4 LFY 1.8 16V Petrol). It has nice power, good consumption, smooth acceleration, etc.

The only problem is when you "LET OFF THE THROTTLE". When I release the throttle, RPM goes down gradually and smoothly but when it reaches below 1000 (approximately between 900 - 800) the engine vibrates and sometimes revs up to 1100 and back to 900 again. After that RPM drops to 800 and everything is normal. The idle itself is a little erratic and not very smooth.

This problem doesn't happen all the time but most of the time the car behaves this way when lifting off the throttle.

I should also add that sometimes (not always), there is a jerkiness when I release the throttle while moving.

I spent lots of time to cure the problem but couldn't solve it.

I suspected vacuum leak. I checked intake and exhaust manifold gaskets, throttle body gasket, brake booster hose, oil vapor hose gasoline vapor hose and they all seemed to have no leaks. I disconnected the whole throttle body from the car and tested it for leaks. I could find a little vacuum leak in throttle shaft seals. I fixed that leak but the problem still exists.

I suspected stepper motor and even replaced it with a brand new one but no improvement on the situation.

I suspected Throttle Position Sensor but according to voltage test it doesn't seem to be faulty.

This issue is not related to temperature because I discovered that it occurs whether the engine is cold (during start-up) or warm (operating temperature).

To help you understand the issue better I recorded a video when the car behaved that way.

In this video I first rev the engine to 2750 RPM and after that I release the throttle completely. If you watch it carefully you will notice self-revving of the engine between 00.07 and 00.09 in the video.

Here is the video:
https://www.mediafire.com/?sjnjjh9djcf1qq0


I also noticed something strange when I released the throttle. I disconnected the intake hose and started up the engine. Now I could see the throat of the throttle body and the tip of the stepper motor and the throttle butterfly. With the engine running, I opened the throttle a bit and released it to see how stepper motor performs while the engine returns back to idle. I saw that when RPM dropped to about 900, the tip of the stepper motor fluctuates back and forth and then after about 2 or 3 seconds it almost stabilizes and the engine revs back to normal idling RPM (which is 800).

I even recorded a video of stepper motor fluctuation! Maybe it helps to diagnose the problem.

Here is the video:
https://www.mediafire.com/?pfmphc3ib8hl1rc

You can see the stepper motor fluctuation in the above video (after I release the throttle) between 00.13 and 00.16 and also between 00.22 and 00.25.


This is my throttle body and the tip of stepper motor:





I also noticed that the engine vibration happens exactly when the fluctuation of stepper motor happens! I know that stepper motor isn't faulty because I replaced it but it behaved like the previous one. What can cause the stepper motor to act like that? Vacuum leak? TPS issue?

Now I feel tired and helpless and I decided to replace the whole throttle body to solve the problem. :(

But I thought that it is better to consult you before replacing any part.

Thanks in advance for your useful recommendations.
 

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Hi everyone,

My car has a weird idling problem which is difficult to diagnose.

The engine itself has no problem (XU7JP4 LFY 1.8 16V Petrol). It has nice power, good consumption, smooth acceleration, etc.

The only problem is when you "LET OFF THE THROTTLE". When I release the throttle, RPM goes down gradually and smoothly but when it reaches below 1000 (approximately between 900 - 800) the engine vibrates and sometimes revs up to 1100 and back to 900 again. After that RPM drops to 800 and everything is normal. The idle itself is a little erratic and not very smooth.

This problem doesn't happen all the time but most of the time the car behaves this way when lifting off the throttle.

I should also add that sometimes (not always), there is a jerkiness when I release the throttle while moving.

I spent lots of time to cure the problem but couldn't solve it.

I suspected vacuum leak. I checked intake and exhaust manifold gaskets, throttle body gasket, brake booster hose, oil vapor hose gasoline vapor hose and they all seemed to have no leaks. I disconnected the whole throttle body from the car and tested it for leaks. I could find a little vacuum leak in throttle shaft seals. I fixed that leak but the problem still exists.

I suspected stepper motor and even replaced it with a brand new one but no improvement on the situation.

I suspected Throttle Position Sensor but according to voltage test it doesn't seem to be faulty.

This issue is not related to temperature because I discovered that it occurs whether the engine is cold (during start-up) or warm (operating temperature).

To help you understand the issue better I recorded a video when the car behaved that way.

In this video I first rev the engine to 2750 RPM and after that I release the throttle completely. If you watch it carefully you will notice self-revving of the engine between 00.07 and 00.09 in the video.

Here is the video:
https://www.mediafire.com/?sjnjjh9djcf1qq0


I also noticed something strange when I released the throttle. I disconnected the intake hose and started up the engine. Now I could see the throat of the throttle body and the tip of the stepper motor and the throttle butterfly. With the engine running, I opened the throttle a bit and released it to see how stepper motor performs while the engine returns back to idle. I saw that when RPM dropped to about 900, the tip of the stepper motor fluctuates back and forth and then after about 2 or 3 seconds it almost stabilizes and the engine revs back to normal idling RPM (which is 800).

I even recorded a video of stepper motor fluctuation! Maybe it helps to diagnose the problem.

Here is the video:
https://www.mediafire.com/?pfmphc3ib8hl1rc

You can see the stepper motor fluctuation in the above video (after I release the throttle) between 00.13 and 00.16 and also between 00.22 and 00.25.


This is my throttle body and the tip of stepper motor:





I also noticed that the engine vibration happens exactly when the fluctuation of stepper motor happens! I know that stepper motor isn't faulty because I replaced it but it behaved like the previous one. What can cause the stepper motor to act like that? Vacuum leak? TPS issue?

Now I feel tired and helpless and I decided to replace the whole throttle body to solve the problem. :(

But I thought that it is better to consult you before replacing any part.

Thanks in advance for your useful recommendations.
when was the car last services and spark plugs changed and have you had it on diagnostics to check for fault codes and live data have a read here http://www.peugeotforums.com/forums/introductions-28/brief-faq-guide-new-members-83170/
 

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Discussion Starter #3 (Edited)
when was the car last services and spark plugs changed and have you had it on diagnostics to check for fault codes and live data
The car has regular service and spark plugs have been recently changed (Eyquem RFC42LZ2E). There is no fault code stored in the computer.

I have also checked live data with engine running and couldn't find anything abnormal to help diagnose the problem but I can provide any information about any PIDs which help to solve the problem.
 

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I suppose you don't have much engine oil consumption (because of worn piston rings)!!
So, i propose the following 4 steps
1. Change gas-petrol filter and check your petrol injectors, they may are clogged, but at higher RPM they open because of more fuel to inject.
2. I hope you have cleaned properly the butterfly body off oil fume deposits, when changed the stepper motor !!
3. Caution... There is different "tip" on stepper motor for aluminum or plastic butterfly body !! Are you sure for it? The plastic body is wearing, V7 motor.
4. Finally,....Also try to disconnect the oil fumes hose that goes to stepper motor aside....if there are too much of oil fumes, these (much fumes) degrades the quality of combustion, thus driving to erratic idling !!
If this, cures the RPM stability, then you have to do engine piston rings, repair !!

p.s I find as normal the stepper motor, tip movement fluctuation, but i think the nose tip, at idle, should have been closed at all, of this by-pass air passage that allows the oil fumes to driven and burned into the engine, instead of let off to atmosphere.
 

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Discussion Starter #5 (Edited)
Thanks a million for your help, giosx!

More info on the car:

1) It has no oil consumption between oil changes. I have never had to add oil between services, so I don't think the rings are worn. My spark plugs are also very clean and dry. The engine is smoke free.

2) Disconnecting the oil vapor hose didn't change the situation and RPM fluctuating (when letting off the throttle) didn't solve. The video I posted earlier was in fact recorded with oil vapor hose disconnected.

3) Yes, I cleaned the whole throttle body very carefully before and after Stepper Motor replacement. (My engine is always clean and tidy).

3. Caution... There is different "tip" on stepper motor for aluminum or plastic butterfly body !! Are you sure for it? The plastic body is wearing, V7 motor.
This was very interesting to me!

Could you please explain a little more about the kind of stepper tip for plastic throttle body? How does it look?

I had also thought about throttle body wear due to stepper moving back and forth.

I bought the new stepper motor in a shop in which they had a new engine and they disconnected the stepper motor directly from the engine and sold it to me. So, it is probably the right stepper motor the manufacturer put on the engine and it must be OEM. I tried with another stepper motor and no change at all.

Could it be a leaky fuel injector?

If it is a fuel injector problem why it happens only when I let off the throttle?

If it is a fuel injector problem why my car has excellent acceleration and tractability and no fuel consumption problem?

I have read that if the injector(s) leak, there will be strong gasoline smell in the engine bay but I don't have it.

Is there a way to diagnose fuel injector problem (leak or clogging problem) with looking at LEXIA or PP2000 live data?

I think that clogged injectors result in increased pulse width, is it true?

My injector pulse width @ idle is 3.0 - 3.1 ms (operating temperature)

Thanks again for your help.
 

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These are the 2 different stepper motors
part number 7514022 V7 for plastic butterfly body
and
part number 7514013 for aluminum butterfly body
Their difference is on the tip !!
Ρελαντί 7514013 για βάση &.jpg

Ρελαντί 7514022 για βάση &.jpg

Also i suggest to clean your injectors with ultrasonic cleaning
a dirty/cloged injector cause problems especially at low RPM, because at High RPM there is a lot more of fuel and pressure at the injectors, so there is not real problem at high but only at low RPM.
I hope i helped you.
p.s. Adjust you spark plugs at 0,90 mm
 

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Discussion Starter #7 (Edited)
Thanks again for your answer!

That was really valuable information! I haven't heard of Stepper Motor Tips for different throttle bodies!

This is my stepper motor:






So, according to what you said my stepper motor tip seems to be the correct one for plastic throttle body:


So, the theory of stepper motor tip is excluded.



I had also set my spark plug gaps to 0.9 mm and they are the ones recommended by Peugeot for this engine (Eyquem RFC42LZ2E)



The only problem as you mentioned is injector cleaning. I don't think that my injectors are clogged but I will try it.

But there is a problem:

In the area where I live, mechanics don't know how to clean injectors properly with ultrasonic device and I fear that they damage my injectors during the process! (removing and cleaning)

So, I prefer to clean them by pouring injector cleaner (those that are sold for PSA cars) in my tank rather than removing injectors from the car.

I know that ultrasonic way will have better results but I don't risk damaging my injectors in the hands of untrained mechanics!
 

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Discussion Starter #8
Update:
I changed throttle body and the problem almost solved because throttle shaft seals were leaking.


I now have only one problem. When I start the car at morning, idle fluctuates a bit (between 900 - 1000) but it happens only when the engine is cold. After about 10 to 15 minutes the idle becomes stable.


I made a video of the aforementioned idle fluctuation.


Video Clip:

https://www.mediafire.com/?7kzhw8u793b9g4a




If anyone could help me to solve it, I will be much appreciated.

It is very strange that it only happens for about 15 mins!

I suspected coolant temp. sensor but it passed my ohm test.

It could be stepper motor but i suspect because if it was, it should happen all the time regardless of temperature.

It is a temperature based problem.

I now suspect TPS, but I am not sure if it proves faulty only at certain temperatures.
 

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Its normal to fluctuate in the morning with cold engine.
One thing i forgot to tell you is to remove/unscrew the throttle position potensiometer, from the throttle body and to lubricate it, with lubricant spray.
Just spray it around the plastic center and turn it by hand, so the lubricant will go into it (until you will fell it, more easy to turn around).
This action is good for it, as for any potensiometer, it will make it to work better when it gives the position of the throttle!
Also dont forget to apply a small "film" of grease/lubricant at the axis of the throttle body.
Also apply grease a small "film", when put the body to the intake manifold and everywhere, when assembly the stepper motor also a small "film".
I hope this will help you a little more, so not the air passes thru and make irritations on engine working.

The picture below, is just an indication of a typical potensiometer !!
http://skemaku.com/wp-content/uploads/2015/04/potensiometer.jpg
 

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Discussion Starter #10 (Edited)
Thanks again for your advice Mr. giosx

I bought a brand new OEM throttle position sensor and I want to install it.

I also bought an original Magneti Marelli Stepper motor which is very hard to find. I keep it in reserve for later.


One thing i forgot to tell you is to remove/unscrew the throttle position potensiometer, from the throttle body and to lubricate it, with lubricant spray.
Which kind of lubrication do you mean? Engine Oil? Grease?
Are you sure oil doesn't damage TPS?


Just spray it around the plastic center and turn it by hand, so the lubricant will go into it (until you will fell it, more easy to turn around)
You mean spraying into this area?



Also apply grease a small "film", when put the body to the intake manifold and everywhere, when assembly the stepper motor also a small "film".
Between throttle body and intake manifold there is an O-Ring. Applying grease around that O-Ring?

I hope this will help you a little more, so not the air passes thru and make irritations on engine working.
So, you want to say that grease cures vacuum leak? (if it exists)

I will try it.
 

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You got correct the meaning... These are standards to follow always !! :thumb:
Spray it (Air Throttle Position Sensor (TPS) VE378011) with any spray lubricant, just like the rusted bolts or doors or any moving wire !!
Put a film of grease between any contacting area when assembly 2 parts.
Put a film of grease in any o-ring, it will remain elastic and no air, will pass!!

i wish you upload a photo of the throttle body and the part number code for it

Air Tip Of Stepper Motor.jpg
Here at the engine air intake (throttle body), are the 2 most important parts:
Air Temp-Air Volume Meter and Idle Stepper Motor and their part numbers,
for other 406 owners to be helped. :)

LOVATO Easy Fast Smart Kit 210.00€+ΦΠΑ 48.30_258.30EUR.jpg
Another info: My 406 run with autogas (butane) also!! I put (2 years ago) and runs excellent,no problems with 40-50% lower cost and with the 2 full tanks (70Liters gasoline and 55 Liters butane) it goes for almost 2.000 KM travel !! This system i use is: LOVATO Easy Fast Smart Kit
 

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No photos

DEAR FRIEND !!!

Please reupload the photos because there where you upload these pictures, there is this message !! So there are NO photo's... :nono:

>>>>> This Account has been suspended. <<<<<< :(
 

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Discussion Starter #15 (Edited)
I uploaded them again dear Mr. giosx!

Here you are:










Should i apply grease here? (where stepper tip goes back and forth)




 

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No grease at where the tip goes into... !!!!
But apply grease to the elastic o-ring and the surface ( of the 2 screws)
of the stepper motor !! - So there will no "outside air" will pass.

The principle of operation for the stepper motor, is to open-half open-full open, depending of the engines rpm, so it lets opening for the oil fumes, to be absorbed and then to burned in the engine.

What is the part number for the plastic throttle housing ???
 

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Discussion Starter #18
What is the part number for the plastic throttle housing ???
I don't have the box but i took a picture of all the writings on the throttle body.

It turned out that my previous throttle body had vacuum leak in throttle shaft seals. I could hear the air being sucked through the hose that i put into my ear to listen to hissing sound around throttle body.

But this new throttle body doesn't have that vacuum noise which means it is perfectly sealed.

You forgot to answer my last question about the gasket between intake manifold and throttle body:



Should i apply grease to these areas???



 

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I don't have the box but i took a picture of all the writings on the throttle body.

It turned out that my previous throttle body had vacuum leak in throttle shaft seals. I could hear the air being sucked through the hose that i put into my ear to listen to hissing sound around throttle body.

But this new throttle body doesn't have that vacuum noise which means it is perfectly sealed.

You forgot to answer my last question about the gasket between intake manifold and throttle body:



Should i apply grease to these areas???



Yes apply grease on that area !!! ( i wrote it before apply a thin film of grease on contacting surfaces) it makes better contact, no dust to go in ...and no problem because you have put some grease !!
Also when you pull out rubber hoses (water pipes) always apply grease inside at the where goes into pipe, by this the hoses keep elastic and can be pulled out easy.

Remember to take out the throttle body and clean with spray cleaner the area where is the stepper motor and the stepper motor tip, because too much carbon by the engine oil fumes, accumulates there!!
Do this every 30-50.000KM :lol:
Have a good day my friend.
 

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Discussion Starter #20 (Edited)
Hello again Mr. giosx!

Thanks again for your helpful recommendations!

I did what you said and it improved idle fluctuation at cold start-up a bit but didn't cure it completely.

In the meanwhile, I noticed something strange which may be related to my idling problem!

I noticed that after some "downhill" cruising, when i come to stop the car idles higher than normal for about 3 minutes or so! It idles at about 1200 rpm! But if i open the throttle and release it the idle comes back to normal 800 rpm.

This happens especially cruising downhill in "neutral".

Can this be related to my previous idle fluctuation issue?
Can a faulty VSS (vehicle speed sensor) cause this problem? What about brake booster?

What could be the reason for this strange behavior?
 
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