No vacuum leaks, been over everything with a spray can.

'89 doenst have codes. I think it was the last one not to.

Work currently aborted due to rain

''reconsider the water sensor and the resistor you installed'' reconsider what? It stopped the 1200+ rpm idle at ~80c

FWIW, the pot adjustment was made by sliding the full assembly up / down from the far right.
What does the itty bitty adjustment towards the center actually adjust ?

My car has a similar idle problem and the fault codes and these are what I had initially:

"7 TNA (Engine RPM) Signal
14 Road Speed Signal At CIS-E Control Unit
18 Current To Idle Speed Air Valve
27 Data Exchange Fault Between CIS-E Control Unit and EZL ignition Control Unit"

Cleared the codes and the only one that still comes up is 14. From what I have read, most common issue is the failure of the hall effect sensor that is on the back of the speedometer. Other potential issue is the CIS computer itself.

I have a likely good used one that is waiting to be installed just haven't been able to do that in the past 4 months. My issue really isn't that bad atm.

Part number is 0075422917, should be about $55 at the dealer.

89 seems to be a production break point.
Your 93 electronics are different than mine but thanks

I believe the inside diameter of the mechanical valve is 1/2". The IAC is Normally Open unpowered, so that's why your idle is high. Try the gate valve idea, less than $10.

The potentiomiter
 

Potentiomiter may be the problem ,remove it and check out the carbon track if worn its shot.

If you unplug your air idle control valve the revs should be about 1200 to 1500 rpm - do you still get that after your resistor modification?

As for the little adjustment thing in the centre of the potentiometer that's the fine tuning. "Everyone" says don't touch it.

He's already done that I think

If you don't have the ability to measure fault "blips" then I believe the fault codes are given in terms of on off ratio aren't they?

Potentiometer is brand new, no change

I dont know bout the fault codes

tilac, sure cant hurt

Tnbob Take the vacuum pipe of the brake servo and check vacuum with a guage .And if it fluctuates with it off the problem is on the engine side. Blockthe pipe with a bung then If it is stable your brake servo is leaking vacuum.

opti... thats one I actually havent tried yet.

tnbob let us know please how you get on with it .

rain, wind and coool postponed work

for new readers/problem solvers, here is a recap
New cap and rotor
New fuel distributor
new EHA, torx's replaced with flat head screws
new pot on front of FD
NEW vacuum hoses to and from the IAC, one to the block is a real (&^*(&^*
IAC replaced with used one, both tested good.
OVP relay replaced, no change
New injector boots
New temp sensor with resistor mod.
The temp sensor stopped the high (1200ish rpm) idle

Vacuum leak checked with carb cleaner spray. NONE found

Things to do:
Confirm alternator voltage regulator is working properly
Change fuel pump relay with new one.
Replace IAC with gate or ball valve setup
Start a mold for some type of as of yet unknown shaped charge

I did find a nice pictorial of how/what/who the IAC is supposed to do.

http://www.k-jet.org/img/articles/diagrams/cis_system1.jpg