A couple things that are often glossed over on high idle (other than air leaks into the intake manifold which you seem to have addressed) and that is the sensors. The voltage/circuits are low values so any sensor connections (including connector to ECU) must be clean and not oxidized in any way. Clean then with contact cleaner (not just a solvent) to make sure there is no voltage drop across them. I like to gingerly use an old toothbrush to help it along. First sensor is the thermo time switch which turns on the cold air injector when the engine and air is cold. It's working or you wouldn't be able to start the car from cold. It turns itself off by way of electrical heating coil in a handful of seconds (depending how cold it is). If it didn't the cold air injector would continue to run keeping idle high. However, there is a secondary sensor which is the temp sensor that measures coolant temp that also controls the cold air injector, keeping it off when the engine is warm and the cold air injector is not needed to start the car. It's other function is to keep the main injectors open a little longer by feeding a signal to the ECU until the engine warms up. If the signals are off either because of faulty signals/dirty connections you could get high idle. While you can measure resistances etc. substituting these two sensors with new can pin point a bad sensor. Once warmed up the idle is set by a lock nut/bolt by the butterfly valve in the throttle body.
So clean contacts (almost free and should be done anyways), see if you can set adjustment on throttle body (free), Temp sensor (not temp gauge sensor) smaller cost, maybe even thermo tome sensor switch (a little higher cost). I'm not sure about oxygen sensor as it's a fine tuning device, pretty reliable and replaced at a predetermined interval, some L jetronic systems didn't even have it (BMW etc)although shouldn't be ruled out. ECU lastly. The ECU's are Bosch and pretty reliable, the TR8 ones from Lucas not so much (what else is new?)
- - -TR7 Spider - - - 1978 Spitfire- - - - 1976 Spitfire - - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT
