2002 xsara picasso 1.6 engine 'surging' off idle

[griffo]

hello, i am new here so apologies if i don't do this right!

i recently bought a 2002 xsara picasso 1.6 (i know, it's old, but it's a stop gap until i get a newer car) that has done 160k with timing belt replaced at 100k.

i just went on a 25 km round trip and when i arrived home i noticed the engine appears to be what i would call 'surging' at idle - the revs do not drop immediately and then the engine revs up a few times.

i tried to record a video but the phone makes it sound like grinding gears!

can anyone suggest the cause?

thanks!

griffo.

[griffo]

p.s. - it's a petrol engine. i have a citroen ecu reader that has shown no error codes.

[ozvtr]

I assume it's a TU5JP4 engine?
Could be a vacuum leak.
Check the inlet manifold is secured to the head correctly.
Being plastic there may be a split or crack in the inlet manifold. Spray carb or brake cleaner around the inlet manifold, see if engine revs change. Don't spray that stuff on hot surfaces it's flammable!
Check the vacuum line from the inlet plenum to the brake booster.
Plug the line from the brown purge valve to the inlet plenum at the plenum. Valve might be stuck open?

Not too many sensors on the TU5. Oxy, crank angle, and MAP.
You could disconnect the MAP (Manifold Absolute Pressure) sensor electrical connector and see if the engine runs better or worse?

[griffo]

hi oztvr.
thanks for the suggestions. makes sense.
i am embarassed to say i dont know how to tell if it is a TU5JP4 engine!
i have only previously owned diesel citroens.
griffo.

[griffo]

hi there, i took the car back to the place i bought it and the machanic agreed it was either a vacuum leak or possibly the idle regulator valve, a common fault, apparently. luckily it is still under guarantee and they will fix it.
i always find it is best to go 'armed' with at least basic knowledge when visiting a garage!
thanks again.
griffo.

[griffo]

hi all, it was the idle regulator.