dodgy idle, ne elp?

hi, ma punto 55 manages to idle high for a while then drops and ticks over really nice and quiet, but then idles say just over 1100revs ( if i had a rev counter ) wasent that annoyin but now ive fitted a cherry bomb bk box and k n n induction kit so now sounds reli loud so very annoyin. cheers for any help. rob

From your thread I think you've done some car modifications now there is a problem with the idle. Would imagine the car has some sort of idle control motor which may need replacing. Try resetting the ECU first.

sounds to me as though you had a problem and the modified it? if thats right, first of all thats really dumb, but secondly, its probably an idle control valve and should be straightforward to replace. was one bolt and a plug on my old fiesta

it is difficult to accuratly determine what rpm the idle is at simply by listening to it. you can get a cheap rpm counter that simply attaches to your battery or you hold it near a cam sprocket (depending on type). i would check the rpm before assuming it is high.

if the rpm is high then there are 3 main areas to consider.

1. vacuum leak. even if the car is happy and healthy, a vacuum leak will result in a high idle. check all vacuum hoses on the intake for cracking or splits.

2. idle speed control actuator fault. the ecu will try to maintain the correct idle rpm. it uses an actuator to do this. if the ecu can not omve the actuator then it cant control the idle rpm. a scrapyard throttle body is the cheapest and easiest way to replace it. since your rpm drops after a while it suggests the ecu can control the rpm so this isnt very likely.

3. coolant temperature sensor fault. if the ecu thinks your coolant is cold even when it warms up then it will maintain a cold idle constantly (usually 1100-1300rpm). you can test your coolant temp sensor by measuring its resistance to see if it alters as the engine warms up. since your rpm drops afer a while it suggest the ecu knows what temp your coolant is so this isnt very likely.

i thin number 1 is the most likely, either that or there is nothing wrong with your idle. that is why i suggest you measure the rpm before assuming it is high.

in future please use english in your posts. i know the english language is difficult to master and state schools have let you down, however a spell checker is provided by the forum to make life easy for you.