91 80q surging idle

[Jim Bresee]

Howdy,

 

My sons 1991 80q idles fine when cold, but as soon as it warms, the idle
begins surging about 400 rpm with a 1 second cycle time.

 

Here's what I've tried so far to diagnose it:

1.	looked for vacuum leaks - did not see any
2.	Removed the electrical connection to the ISV - no change.
3.	Removed the electrical connection to the WOT and IDLE switches -
engine races
4.	Checked resistance on idle switch - 9.6 ohms at idle, open when
throttle is advanced.

 

Any idea what I should look at next?

Thanks!

Jim