Is the ECU causing this fault-Please help!

[lakemaligne]

Hi all, I have owned a MK1 1996 2Ltr LX petrol 406 from new. The car has covered 152,000 trouble free miles apart from a leaking A/C compressor. The problem I am having started over a year ago. 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 moving forward or backwards! During this period the car will also jerk, as the power comes off when i completely lift of the accelerator ,instead of the usual smooth transition from engine driving the car to using the engine to gradually slow the car. 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. The tick over instantly drops to normal once the car has stopped moving, which seems to suggest that a motion sensor of some type is involved with this fault. On some occasions when I start the car form cold, the tickover is very erratic ,one second revving at 1200 rpm and then back down to 900 rpm.It cycles like this until the engine starts to warm up.The dealer I originally bought the car from replaced the MAP and oxygen sensor to try and sort the problem, but that only caused the engine fault light to start appearing, which until this point had never appeared in the cars life. The jerking and high tick-over still remained. They then replaced the throttle pot and cable and reset the adaptives, but still the fault kept appearing. The fault is not linked to changes in driving conditions ,ie heavy rain or dry spells, or bumps in the road. The vehicle tech who worked on the fault said that the ECU had recorded an "intermittent fuel regulation fault"(MP511), but was getting a reading of Lamda1, and said that his laptop was showing emissions levels of that of a new car, and everything was spot on, but agreed that the symptoms I described existed. Out of desperation ,I have since taken my 406 to another dealer who have got their master tech on my case. He ran a diag test which showed up intermittent MAP sensor, which he replaced. The car ran like a dream for about a month, then all the problems came back. He then replaced the steppor motor as it was sticking, which he demonstrated to me. Diags were still showing intermittent oxygen sensor ,but he said that this was not causing my symptoms, so said to ignore it unless it went completely .Has any one any suggestions please, as this car drives exceptionally well 99% of the time.Could a dry joint within the ECU be causing this fault, and if so can these things be tested accurately. Does any one know of any trusted ECU testers that live near Rugby/Coventry.

[mjb]

So new throttle pot, stepper and map sensor... but it's still misbehaving.

Only thing I can think of would be if your throttle body is gunked up inside causing the butterfly to not close properly. In this case as far as the ECU's concerned, you're still pushing the pedal a bit. Take off the air hose (probably just a jubilee clip) and with one hand holding the throttle open from the outside, get in there and clean it with some carb cleaner and a rag/cloth/kitchen towel/etc

[lakemaligne]

Hello MJB,I will do as you suggest this weekend. Would ordinary petrol or meths do the job.Would you not have thought that the vehicle tech would have tested for this and cleaned out the throttle housing as a matter of course.The car is starting to hesitate now if i pull off normally but gently ,it's almost like i am keeping the acelerator pedal in the same position ,but in fact I am depressing the pedal.When i first start the car in the morning,the tickover races up and down,until i rev it hard for a few seconds,and this seems to clear it and the tickover settles to the normal level under "choke " conditions,ie, 1200rpm.

[lakemaligne]

Hello MJB,I removed the hose from the air box and inspected the butterfly for movement and contamination,and it worked fine and was spotless. Inside the throttle housing ,just in front of the butterfly, I discovered an orange ,small round object which resembled a small capacitor,and wondered if you knew what it was. My guess is that it is an air temp sensor!,am i right.

[lakemaligne]

MJB,I have read your reply to my other post ,and am not sure I understand what you are suggesting,or why you have locked me out. I posted my problem under "Mechanical" to see if it caught a wider audience,as my dealer who is trying their best with the fault my 406 has ,are now suggesting it "could be" an ECU fault ,which is why i orignally posted under "Electrical".

[Captain Jack]

There's no point posting the same thing under different sections as most people use "New posts since last visit" feature and see all er.. new posts since last visit. It won't be missed.

Can't help with your issue though, I am afraid.

[lakemaligne]

Hello Captain Jack,thank you for your advice.You have probably gathered that i am not a frequent user of this site and do not know the various tricks regulars are aware of to find new posts.. MJB put in his initial reply to me and i quote "Hint: Try using the 'Enter' button on your keyboard. You'll find more people might want to read what you have written". Now whether this was sarcasm or he was trying to genuinely tell me how i could get more people to read my post,I just dont know.At least you have had the courtesy to reply to my last message.I am annoyed however that he has "locked" that particular posting because it now means that if anyone had got any ideas on what is causing my fault,they can no longer reply.For the benefit of any body else who may be reading this, my car's idling speed now drops to around 500 rpm every time i stop at a junction ,and keeps trying to die.The fault light also comes on about 5 seconds after the car's idling becomes erratic. My Peugeot dealer is going to replace the "Oxygen Sensor" next week ,as it was after having had the original "Oxygen Sensor" replaced by the the first Peugeot dealer which caused the fault light to appear in the first place .I know i am probably grasping at straws ,but i cannot help thinking that as the replacement oxygen sensor caused the fault light to appear,and it now come's on each time my car displays fault symptoms.The master tech at the dealer has told me that the recorded fault code is showing "Intermittent Oxygen Sensor".

[mjb]

I wouldn't have thought it would be the oxygen sensor at fault (more likely the guy fitting it made a mess of something when he was doing the job), but if the ECU's recording faults with it, I guess there's a reasonably high probability a DOA (dead on arrival - faulty new part) sensor was fitted. You could well find that having someone who knows what they're doing re-fit it will solve your problem even if it's not the oxygen sensor at fault.

I gave you the hint of splitting your posts into paragraphs as it makes them easier to comprehend. There was some sarcasm in there, but it's still a very valid tip.

Also, in nearly all forums on the internet, moderators will close or delete duplicate threads as it keeps the forum tidy and stops multiple confusing conversations about the same thing. The moderation here on 406oc is very lax compared to others and the mod team don't use the tools available to us to make points or interfere with threads unless absolutely necessary - we're just caretakers (and occasionally mediators).

[legoless]

Edit:Sorry thought it was for a 2.1 diesel

Do these have a water temp sensor like the on the 2.1 diesels......theyre prone to fail?

[mjb]

Edit:Sorry thought it was for a 2.1 diesel

Do these have a water temp sensor like the on the 2.1 diesels......theyre prone to fail?

Pretty much every car built in the last 15-20 years (well, with fuel injection at least) has a coolant temperature sensor, and they're all prone to failure

[lakemaligne]

My dealer has replaced the oxygen sensor on my request I hasten to add,and you were right MJB ,it has not fixed the problem.The fault light is still coming on for 5 seconds a couple of times a day,and the tickover races up and down when I am in neutral at a junction. The errattic tickover is worse when the engine is started form cold. The original jerking fault has however not shown up for several weeks now.What this means i dont know,but the Master Tech who has been working on the car ,along with the Service Manager are now convinced it is an intermittent faulty ECU.They cannot accurately diagnose this though.

I now need to look for a reliable trusted ECU testing establishment. So I will be adding another post soon asking if anyone knows of one they can recommend in the Midlands area somewhere near Coventry. If any body reading this knows of one ,please reply.

[mjb]

I now need to look for a reliable trusted ECU testing establishment. So I will be adding another post soon asking if anyone knows of one they can recommend in the Midlands area somewhere near Coventry. If any body reading this knows of one ,please reply.

Could try the recon places:
viewtopic.php?f=17&t=6471&p=64769&hilit ... ecu#p64769
viewtopic.php?f=1&t=4498&p=43352&hilit=recon+ecu#p43369

[TopDonkey]

Is the stepper motor you replaced the same as the idle air controller valve ?, i would have said this would be the first place i would look.

And i'm not sure if your engine uses the crank position sensor to determine when to fire the plugs ?, if so, this could be going intermittent ?, but i have a feeling that the crank sensor on your engine is only referenced whilst cranking the engine on startup (might be wrong, and cant remember where i got that information from though!)

Can you get a timing light on it when its going wrong to rule out an ignition problem maybe ?, it could be a weak coilpack causing the idle air controller to over and under compensate resulting in the wrong mixture and erratic throttle response maybe ?.

I would have said its a very very slim chance that the ecu is actually faulty, and the test centers that test ecu's usually use a simulated test rig that doesnt load all the ecu outputs correctly so it will probably come back as tested and ok even if there is a fault, it would need to be diagnosed and tested on a car really

[lakemaligne]

Topdonkey,

I am fairly sure that the stepper motor, is the idle valve controller on my car,but will double check and get back to you.

One thing i have noticed is that most of the fault symptoms have recently dissappeared since having had the MAP and now the Oxygen sensor renewed, ie, the jerking and the high tickover when i engage neutral while the car is still in motion. I dont know whether my problem is down to a couple of different parts going wrong at different intervals intermittently ,but the symptoms are now different. On some mornings when the engine is cold,the tickover cycles between 400 and 1200 rpm until she starts to warm up a little. Now if i engage neutral at any point the engine revs shoot down to 400 rpm ,nearly stalling ,then it catches itself and ticks over normally .

I wont be able to try a timing light just yet ,but will get back to you when i have

Thanks.

[lakemaligne]

Hello again Topdonkey,to answer your questions ,yes the steppor motor is the same as an idle valve,and i have had this replaced twice during the last 2 years as it did seem like the most logical part to have failed.I have asked the Master Tech who has been working on my problem whether he has checked out the possibilty of an intermittent coil pack,and crank sensor ,and he says they are working pertfectly.We have even discussed the possibility that the steppor motor is oiling up and sticking,due to the fact that the car has done 153,000 miles.But if this was the case ,then it would happen all the time ,and the car is running nicely at the moment.Anyway I spoke too soon ,all the symptoms have now come back ,not permanently ,but now and again.We now both agree that the only thing we can do now is get the ECU checked out,but before I take it to get it tested ,I want to strip it down myself and check it out for dry joints and other obvious faults.Any help on what i should be looking for guys.

On a different matter,I pressed the air recirculating button on the dash monday and i heard a click just as the motor controlling the flap had stopped.Now I cannot get any fresh air into the car,and its misting up pretty bad as there is no fresh air coming out of the small triangular vents in each corner of the dash. .Anyone know whether this is a simple fix or not .I can still hear the motor when i press the switch.