406oc.co.uk

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.

try your idle speed control valve clean it up or replace it if this has not already been done

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Original thread is here: viewtopic.php?f=3&t=8675

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