uneven idle

[paul]

Hello fountains of knowledge, I'm just after a pointer in the right direction.
My car is totally stock and has only covered 47500miles, but since I've had it the tick over is ever so slightly uneven.
Due to an SES light I have replaced the air pump and the purge solenoid, but the uneven tick over remains although with no SES warning.
I have noticed also that a couple of the fuel vapour lines under the hood had had a section cut out of them and metal tube and rubber tube inserted for repair.
Could this cause the problem? as I have checked all the vaccum lines that I can get to.
Many thanks

[Joe 1320]

Check all the air lines.... that tick could be from a leak.

[paul]

I've checked all the hoses that I can access either by visual or by ear and others by 'wiggling' them and listening for a change in idle.

[94 formula]

Where does the tick sound like its coming from? I had cracked manifold and it sounded like it had a tick.

[Injuneer]

An exhaust leak can sound like a "tick", and it can screw up the O2 sensor, causing it to run rich on the side with the leak. Check for an exuast leak.

[paul]

There is no 'tick' sound, I meant the tick over (idle) is uneven.
Sorry, us Blighties speak different!

[Joe 1320]

A scanner would help..... The tick over quality is determined largely by the IAC or idle air control valve. It is primarily responsible for metering additional air into the engine when the throttle blades are closed. If either that or the EGR valve becomes carbon fouled, it may affect the idle. Both can be cleaned.

[paul]

Thank you, I'll check the EGR, but as for the IAC is there voltages or resistance I need to measure?