I've been experiencing a problem with slight surges/jerkiness in town traffic ever since rebuilding my engine.
I have not been happy with the IACV making a clacky racket at tickover. I know it's supposed to open/close to maintain 800rpm or so, but surely not several times a second!
Here is the list of my efforts to resolve it:-
Dismantled and cleaned the IACV - it was a bit sooty.
Checked for overtight K&N on the throttlebody intake.
Checked for intake manifold leaks.
Verified there was a small amount of slack in the throttle cable at rest.
Checked throttle butterfly and cable for smooth operation (lubed the cable, greased the pivots)
Cleaned every wiring connection in the engine bay with switch cleaner - especially sensors and injectors.
Tried injector cleaner in the fuel.
I ought to have know better - it was the water temperature sensor passing inaccurate results to the ECU.
Therefore the ECU was controlling the fuelling for a cool engine - causing overfueling - and probably why the MOT emissions test took several attempts to "pass" the idling tests.
The temp gauge was fine - under half way at all times, but that feeds from the black sensor under the brown one!.
Now I have no more slight surges/jerkiness in town traffic, improved throttle response and a quiet tickover.
So.... for those with MOT emission problems, try changing the brown sensor - only costs a tenner!
For those that aren't sure how to change the sensor here's my method:-
With a cold engine - raise the back of the hood and remove the engine inspection panel.
Locate the brown sensor at the top of the engine near to the exhaust manifold at the gearbox end. It is next to the hot hose outlet.
Disconnect the wiring plug from the sensor .
It is secured by a U shaped wire clip. Use a pair of thin pliers to hold the wire clip and pry one of the sides out with a small screwdriver. Use the pliers to withdraw the clip and the connector will pull apart.
Put the U clip back into the connector's grooves - the clip will automatically open and shut when securing the plug to the new sensor. The plug will only fit one way round.
Have the new sensor to hand and smear a little RTV gasket goo on the mating face where the thread starts.
Some sensors have a metal sealing washer like a bear bottle top - it's worth re-using on you new sensor if it's not already present. Be sure a smear of RTV is present both side of this washer - but don't have any on the threads.
Use a 19mm ring spanner to unscrew the old sensor - you will lose a very small amount of coolant when it comes out.
You might want to have some rags under to catch this.
Fit the new sensor - it's a plastic body so don't try to overtighten it. Tight is good enough.
Refit the wiring clip.
Add a small amount of coolant to the overflow tank - to replace what was lost.
Run the engine until warm - checking for water leaks.
Refit the engine cover etc
Job done.
Hope this helps somebody, Jeff