Hi all,
I have a 1991 TR 4cly. If started when motor is cold, the motor will idle at 2000rpm in park and will drop to about 1100rpm when put in drive. It will also at times sharply hunt up and down 1500-2000rpm when in park. This will last about 4 mins. Then when motor is warm idle will be 1100rpm in park and drop to about 850rpm in drive.

1) How do I test the isc to see if it is the problem?????
2) How do I test to see if it is a ecu problem?????
3) I have been told by a mechanic that I can’t just plug a second-hand computer in it has to be SET after being plugged in. Is this true???????

I have spoken to two mechanics by phone.
The first one said more than likely it is the ecu because the isc does not work until the motor is warm. He said the ecu controls idle speed at cold start.
The second mechanic said he would be pointing at the isc or maybe both. Or maybe a vaccum leak.
I can pay one of them $100 to diagnose the problem. Then I will replace what they say is the problem.
Please help Thanks to all that reply

Forget teh ECU

Generally the issue you have is caused by the Idle Conrol Valve, this gives you the fast idle when cold and is operated by a wax pellet. The unit gets dirty and eventually will stop working correctly

even your warm idle is way too high

Thanks for that, ok where is this wax pellet. So i can look at it and if t=it's not too dear I just get a new one>
Thanks