My Xantia (1.8,8 valve)has had this problem for a while: the engine revs take time to settle when coming to a halt i.e from about 1500 to normal tickover at about 800 rpm takes a few seconds after coming to a stop in traffic ,never actually timed it ,but it`s probably up to about 8-10 seconds at it`s worst.
The only time it has not done this is just after I changed the battery ,which I assume was because the ECU had reset itself.
Strangely enough ,the fault does not occur when the car is stationary and you just rev-up the engine (it just settles quickly to tickover speed)
Could it be the stepper motor ,and can I cure it somehow,maybe by cleaning?
regards
Stepper Motor?
Moderator: RichardW
When driving in traffic and coming to a halt - the engine is under load and then suddenly relaxed.
This is not the case when testing at standstill.
Result is different amount of vacuum in the inlet manifold under the 2 different conditions.
This again points to problems for the MAP sensor - a very common problem indeed.
The MAP sensor would be located somewhere with a small rubber vacuum hose running from inlet manifold - in which case its often a simple matter of cleaning this hose from oily gunk.
Or the MAP sensor is a "oil-sensor-look-a-like" screwed into the bottom of the throttle housing - in which case it's probably on it's way out.
This is not the case when testing at standstill.
Result is different amount of vacuum in the inlet manifold under the 2 different conditions.
This again points to problems for the MAP sensor - a very common problem indeed.
The MAP sensor would be located somewhere with a small rubber vacuum hose running from inlet manifold - in which case its often a simple matter of cleaning this hose from oily gunk.
Or the MAP sensor is a "oil-sensor-look-a-like" screwed into the bottom of the throttle housing - in which case it's probably on it's way out.
Revs dipping when coming to a halt can also be symptoms of a rich mixture. I had an old BMW 316i that behaved in the same way. The mixture was too rich and the revs would bounce when coming to a stop. This would point at lambda sensor, and often overlooked component that does require replacement every 50,000 miles or so depending.
Had a look at the MAP sensor tube(I found it without looking in the manual) and it was clean ,but I gave it a blow through anyway.
I then removed the air intake and found it ,and the throttle housing, were a bit gunged-up ,so I cleaned it all up and checked all electrical connectors ,gave it a run and found the problem to be 90% gone.(still a slight delay in shutting down,maybe a second or two,but I can definitely feel the difference when changing gear)I`m still not sure what was wrong - I know I should have ran the car after each step but got carried away with the cleaning etc.
I also suspect the intake may have been drawing some external air as the clamp was skewed underneath the housing,making it difficult to detect,but I`m not sure as this should have caused some erratic running (?)
It will be given a longer run now to see how it performs.
Regards
I then removed the air intake and found it ,and the throttle housing, were a bit gunged-up ,so I cleaned it all up and checked all electrical connectors ,gave it a run and found the problem to be 90% gone.(still a slight delay in shutting down,maybe a second or two,but I can definitely feel the difference when changing gear)I`m still not sure what was wrong - I know I should have ran the car after each step but got carried away with the cleaning etc.
I also suspect the intake may have been drawing some external air as the clamp was skewed underneath the housing,making it difficult to detect,but I`m not sure as this should have caused some erratic running (?)
It will be given a longer run now to see how it performs.
Regards