On going 406 tickover issue

[lakemaligne]

Hi all, I have owned a MK1 1996 2Ltr LX petrol 406 from new. The car up to two years ago has been trouble free apart from a leaking A/C compressor,and getting through the usual consumables. The car will perform perfectly for several days ,then for no apparent reason the engine tick over will suddenly remain at 1200rpm if I shift in to neutral while the car is still moving, and only drops to the normal 950 rpm once the car comes to a complete halt. This happens rolling forward or backwards! The tick over instantly drops to normal once the car has stopped moving and is stationary which seems to suggest that a motion sensor of some type is involved with this fault. During this fault period the car will also jerk, just as the power comes off when i completely lift of the accelerator ,instead of the usual smooth transition . When I depress the accelerator again, there is another jerk when the power comes back on. This condition will persist for a few days , then clear itself for a few days, then come back again. On some occasions when I start the car from cold, the tickover is very erratic ,one second revving at 1200 rpm and then back down to 900 rpm then back up to 1200rpm.It cycles like this until the engine starts to warm up.Once warm If I go to change down ,say approaching traffice lights ,ie clutch down and foot off throttle,the engine revs bomb straight down to zero and stalls. This is the dangerous bit,because when this happens I loose the powered steering and brakes . The fault light comes on for about 20 seconds several times each trip and records " Intermittent Irregular Fuel Delivery". The Master Tech at the dealer I originally bought the car from has so far replaced the MAP sensor , oxygen sensor ,Thottle potentiometerand stepper motor,and even the throttle cable. He even reset the adaptives and said that he was getting a reading of "Lamda 1" and getting emission levels of that of a new car.I am now wondering if my problem could be with the EGR valve,and was wondering if i could disconnect it and block up the pipe.

So please ,as this has now become dangerous ,has any one any suggestions please, as this car drives exceptionally well 99% of the time.Could it be an intermittent ECU, or does any one know of any trusted Peugeot Speciallists near Rugby/Coventry.

[teamster1975]

Very strange fault, I think everything has been changed that I would have suggested (fouling throttle cable, stepper motor etc).
It may be worth pulling off all the sensor plugs in the engine bay & cleaning them up for starters, I'm assuming it hasn't been overfilled with oil!

[Welly]

'Irregular fuel delivery' suggests to me that the fuel pump is not delivering full pressure. The injector spray pattern will be affected and the engine will think it's going to stall and raises the revs to compensate? - just a thought? very strange though.

[steve_earwig]

I'm assuming it hasn't been overfilled with oil!

Eh? It's petrol, does that make a difference?

Is this an 8 valve or a 16?

Looks like both of them have a speed sensor on the gearbox though...

[teamster1975]

Eh? It's petrol, does that make a difference?

Actually thinking about it, no!

Is this an 8 valve or a 16?

The non turbo 2l is 16v, tubby is 8v.

[steve_earwig]

Aha! Now I know which engine management to shove in Google


(when I get back from having my stitches out )

[steve_earwig]

Is this anything like it? http://www.alfaowner.com/Forum/alfa-145 ... 1-8-t.html

[mjb]

The stalling on top of everything sounds VERY much like a problem with the idle stepper and throttle pot, but that wouldn't light the EML nor record a fault.

Given the fault (with the symptoms), I'd suggest one of the following (from cheapest to expensive):
1) Clogged fuel filter. Cheap and easy to replace
2) Shot fuel rail pressure regulator valve
3) Failed tank purge valve
4) Knackered fuel pump

I don't think it's 3 as that usually gives issues at high throttle levels not at idle, but see if taking the petrol filler cap off cures it.

[Harshan]

could be the speed sensor or some random failure in the ECU. The ECU thing happened to me and it was completely erratic where you can't find a relationship or you can't simulate the scenario.

[lakemaligne]

Thanks for all the replies so far,I will try to answer them in order.
1. I have stripped the ECU down and did not find any obvious faults or dry joints. I will swop it with one from a scrap yard if all else fails,making sure i get the key pad code of course.
2.I ran a restance check using an anologue meter and got a smooth gradual reading in both directions of travel,plus its new so have ruled that out.
3.If the fuel filter was clogged or pump duff or rail pressure reg valve up the creek,would it not effect performance at high speeds,because it's faultless in every other respect ?
4.The fault with The Alfa is similar but i do not get any miss fire at speed .I do sometimes get a slight hesitation when pulling off very gently at very low speeds only.
5. It's a 16 v
6. No oil level perfect.
7. Have cleaned all connectors.
8. Coil pack failed 2 months ago ,now has a new one.

Question: has my car got an EGR valve and could this be intermittently faulty, and checked out or cleaned maybe ?

[mjb]

Here's something I've just thought of. Take the pipe off between the air filter box and the throttle body, hold the butterfly open, and clean all the gunk from the inside of the throttle body. Your problems could well be caused by dirt stopping the throttle from closing properly (and the TPS on early cars is worked by the throttle body, not the throttle cable)

[lakemaligne]

Hello MJB, sorry i should have mentioned that I checked the inside of the throttle housing and it was clean and no play or wear evident in butterfly spindle.

I had a look at lunch time to see if i could spot if there was an EGR valve on my 406 and could not find one. Do you know if my car has one and if it does ,could it be causing my problem.

VIN No :- VF38BRFVExxxxxxxx

[lakemaligne]

I took out the stepper motor (idle control valve) at the weekend hoping to find it grunged up,but it wasnt. I tested the motor resistance using a data sheet given to me by the master tech at my local dealer and it checked out ok. With the SM in my hand i pluggged in the connector and switched the ignition on and off,and the motor gently clicked once but did not move the rod at all,which i though it would have .It then it fell silent ,no matter how many times i turned the ignition on and off.

Should the rod have moved in and out ?

While i was doing this job,i disconnected the oil vapour breather pipe running from the top of the engine to the air inlet connection next to the stepper motor.I then blocked off the metal pipe on the throttle housing and the pipe coming from the engine. I did this because my engine mileage is very high and the breather pipe was pumping in a lot of emulified oily grunge into the air intake which i thought may have been efecting the stepper motor.

In this very cold weather the tickover races up and down until the engine gets warm.Once warm ,the car stalls as soon as i lift of the throttle,which is when i lose the brakes and steering.

[mjb]

Should the rod have moved in and out ?

I have no idea sorry, I'm only familiar with the ICVs used on the tubby and V6... However I think that the "steppers" on the older cars (ie not the ones with motorised throttle bodies) are actually just solenoids which push out due to the electromagnetic coil and get pushed in by the throttle body via a spring, so in that case there'd only be one movement

In this very cold weather the tickover races up and down until the engine gets warm.Once warm ,the car stalls as soon as i lift of the throttle,which is when i lose the brakes and steering.

I know it's not much consolation, but you should still have at least 2 assisted brake applications with a stalled engine

What part of the country are you in? If you're able to get to the Stoke area some time I'd be happy to plug my PP2000 in and see if I can be of any more use figuring this out. I should be able to at least check if all the important bits are working as they should be...

[maxxymilian]

What about a problem with the ignition coil. Over time it damages the ECU, especially Sagem SL96 ones. It's a known probelm with the 406 and other PSA cars using this ECU.