***If there is any doubt or problems with setting the tickover, then the Base_Timing should be checked***
Considering high revs can be caused by a split, or detached vacuum pipe it’s probably best to check these first. You can get an indication of a vacuum problem by taking a pipe off while the engine is running at tickover – the revs should rise, if not, there’s already a leak.
The revs should be the same in ‘normal’ and ‘service mode’
To enter Service Mode
Putting the paperclip in... (Shorting terminal A and B of the (ALDL) Assembly Line Diagnostic Link)... while the engine is running at operating temperature puts the car into “service mode” (CO Adjustment Mode)
To make an adjustment
Locate the idle adjustment screw on the top of the throttle body. Have a flat screwdriver handy. With the engine up to temperature and running, put the paperclip in. If there’s a problem with the base tickover it will rise or fall as the clip contact is made. Adjust to 950RPM – rev the engine slowly to 2000 and back – check and adjust the revs if necessary – remove the clip - rev the engine slowly to 2000 and back – if it’s still 950RPM the job is done, if not, repeat the process. Only make the adjustment with the clip in.
The adjustment is 1½ turns back from fully in to get 950RPM (on Ray's and Gazza's at least)
Turn anticlockwise to increase the revs ... screwing outwards ... opening the valve.
In order to prevent the adjustment moving on its own over time, here's a simple modification using an ordinary tap washer and a small screw.
It is also worth checking the throttle cable. Reference Lotus Service Notes section EC11 para. 20 "Slacken the throttle cable adjuster nuts at the plenum abutment bracket. Hold the quadrant fully closed and pull back the outer throttle cable. Adjust locknut B to obtain a clearance between the nut and abutment bracket of 3mm then push the adjuster against the bracket and tighten locknut A".
There has also been an occasion when a fast idle was caused by the earth wire from the injectors to the manifold being loose, located just above the alternator.
[See here ]