Puzzling accelerator/tickover fault-Please help

[lakemaligne]

Hi all,I have owned a MK1 1996 2Ltr LX petrol 406 from new.The car has covered 149,000 trouble free miles apart from a leaking A/C compressor. The problem I am having started over a year ago. For no apparant 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! 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 accellerator again,there is another jerk when the power comes back on. These symptoms 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. 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. All the symptoms remained also. 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 emmisions of that of a new car,and every thing was spot on,but agreed with me about the car having the symptoms i described .I have since taken my car to another dealer ,as I had a falling out with the one I purchased the car from.This second dealer has also ran diagnostic tests and can only see the down loaded "Irregular fuel delivery" fault.They gave me some "Wurth-SeBesto" petrol additive to clean the injectors to see if that cured the problem,but it has not . I was wondering if my car has such a thing as an "Idle valve" which may be sticking now and then,but I could not find any reference to one in my Haines manual. Has any one any suggestions please. This is a very annoying fault which makes driving my 406 very awkward at times,because she is usually a very smooth,quiet ,powerful car and a pleasure to drive,especially on motorways..
If any one reading this is interested ,i did fix the erratic speedometer fault my 406 developed a while back.
Yours Hopefully,
Paul

[Welly]

Have you read, or tried anything, in this thread at all?......viewtopic.php?f=1&t=3489

It's an annoying thing by the sounds of it! especially with the dealers seeming lack of wanting to help much

[lakemaligne]

Hello Welly,I have had a look at your link,but before i go down that route,I found something on the internet about TPS faults and the symptoms they chuck up,which are practically identical to mine.Have a read and see what you think! http://wiki.seloc.org/a/Throttle_Position_Sensor

[lakemaligne]

Hi all, All the previous fault symptoms have returned since the Tech cleaned out the steppor motor.The car has also died on me a few times since the Steppor Motor was cleaned,which meant that what ever part was causing the problem was about to fail completely.(I hoped)Yesterday she died on me again,and when i restarted her, the idle was all over the place,dropping to 0 and back up to 950 rpm and then back again over and over.It cylced like this for about one minute and the fault light kept coming on and off. I managed to get it to my new found local dealer,who reported that the ECU had recorded 2 faults this time. "Irregular fuel delivery" and now "MAP" sensor intermittent. He got the MAP sensor out the car and discovered that the 1st dealer who had replaced it over a year ago in an attempt to solve this very same fault had not used a genuine part. So he cleaned it out and ran an atmospheric pressure test with the engine off,then with it running,and discovered that the MAP sensor was reading wrong and so was faulty!. So I am now waiting for a new MAP sensor,which will have to wait until the beginning of September when I get back form annual leave. i will keep you posted.

[robb]

I am having the erratic rev counter and idling after cleaning the stepper motor today also stalls every time Il et the revs off