Idle speed issue
 

Having trouble holding idle speed. My idle holds fine normally right around 900RPM. But as of last week it's having an issue, when I come to a stop it drops down to about 500, shudders a bit then climbs slowly back up. Kinda like the famous "NA shudder."

The idle speed controller seems to work, when I turn the A/C on it keeps it steady, and it is returning it to 900.

I have so far, cleaned the throttle body. Adjusted the TPS since I was not hearing a click on throttle close. I have also checked for vacuum leaks and such, I did not find any "yet."

Any ideas?

I have a similar problem Scott...I was told it was probably the idle stabilizer valve (ISV), perhaps the TPS, and maybe the 02 sensor...

I was going to clean the ISV but have been told by a knowledgeable tech they do wear out...I plan on replacing that, the vacuum hoses but ran out of money/patience while I was putting the motor back together...If that doesn't work then the TPS, etc, etc, etc... :)

Thats hopefully what is wrong with mine. It seems like it's sluggins to open and close the valve. I did remove the intake manifold a week ago and try and clean it up, but the brushes were very worn.

My 86 951 does the same thing I will take it out of gear it to stop it drops down around 500 or so and then moves up but it's idles at around 750 any ideas what that could be? I did the head work few months back but it did that before I did the head.