I have a 2006 1.6vvti Corolla series IX and due to fluctuating idling speeds, decided to clean the throttle body. After removing the air intake from the TB, I opened the butterfly valve and, using a toothbrush and a little solvent, removed the oily residue (and there was plenty of it) from inside the TB and also on the reverse of the butterfly valve.
After refitting everything, I started the engine. The only difference now is that for the first two or three minutes the tick over speed is around 2000 rpm dropping to around 1100 rpm then after another five minutes to 700 rpm.
What has caused this change? I'm concerned it may fail the MOT due to emission problems.
This may be an old chestnut but any advice would be appreciated.