1.4 16v Megane High Idle speed

[Iceberg_172]

Hi folks, My Uncle has a 2004 Megane 1.4 16v on 90k. Besides the point that its never had the belts done which is another matter lol it has developed a problem with its idle speed.

When the car starts cold it sits around 1100rpm, once you have set off and the car has warmed up, the idle speed seems to sit around 1750rpm. When you come to a junction and disengage the clutch the revs drop right down to around 800rpm for a second then go away back up to 2000rpm and ease off to 1750rpm.

Also, when cruising along at 60mph in 5th gear the car has a very slight judder/misfire.

A bit of background information, he had the ecu changed by a local mechanic due to it idling very low, about 3 weeks later the ecu change the high idling problems started.

I have had a look at it and checked breathers and the throttle body etc and all seems fine.

 

[Iceberg_172]

sorry should have mentioned, there are no warning lights and no fault codes stored.

 

[Sean6545]

Had a k4j megane 2 do this before. Took a while to diagnose but it was he alternator. Wasn't charging fully and the ecu was bumping up the idle speed to increase the charging output.

Try disconnecting the alternator and retest.

 

[Iceberg_172]

i tested the power at the battery with the engine idling at 1750rpm it was reading 14.34

 

[Sean6545]

Try disconnecting it anyway

 

[Iceberg_172]

ok will give it a go, thanks.

i heard that it could be this by a friend so only really checked it at the battery.

by rights, when i disconnect it, the voltage should drop to 12 or just below but the csr should idle normal then?