Strange idle issue

[SIIaCanuck]

This morning on the way to work I ran into an odd idle issue.

 

I pulled off the highway after cruising for an hour+ and arrived at some lights.  As I downshifted (5 spd) I noticed that the rpm wasn't dropping between shifts but hanging up around 2000rpm.

 

When I stopped at the lights, it sat at 2000rpm for a few seconds then slowly decayed to 1600.  I blipped the throttle and it dropped back to about 1400 and then slowly settled to about 1250 by the time the lights changed (couple of minutes, it's a busy overpass with a long light delay).

 

It continued to repeat at each stop/corner to work (another 4 stops).  Once in the parking lot, I let it settle to 1400ish then cut the engine and immediately restarted.  It started completely normally and settled to a normal idle with no issues.

 

Any thoughts on what might be happening?  Am I looking at something failing (sensor)?

 

It's a stock (engine) '95 GT with about 175,000km on the clock (110,000mi).  I'm running a 3.9 rear end with a stock T-5 and a DM SpeedCal to correct the speedo.  I cruise at about 2350rpm on the highway at around 110 kph (70mph).

 

Stew

[Det_Riot]

First thing to do would be to do a base idle reset which i believe includes cleaning your Idle air control valve and checking the voltage to your throttle position sensor. If that doesn't solve it, next step would be to replace the IAC. That's usually the culprit in a hanging idle

[Josh@RideTech]

First thing to do would be to do a base idle reset which i believe includes cleaning your Idle air control valve and checking the voltage to your throttle position sensor. If that doesn't solve it, next step would be to replace the IAC. That's usually the culprit in a hanging idle

 

Exactly what I'm thinking.

[Det_Riot]

http://www.allfordmustangs.com/forums/5-0l-tech/340926-how-do-base-idle-reset-how-check-set-your-tps.html

 

Here's a pretty solid guide