89 k1500 slow to return to idle between gear changes.

[Jebadiah]

A few weeks ago I got an 89 k1500 short bed 4x4 with a 350 and 5 speed manual. I've been noticing that between gear changes it takes absolutely forever to come down to idle, which makes it difficult to get a smooth shift. It also never fully drops until the truck has come to a complete stop. If I push the clutch in while moving, it will drop to about 1200rpm, then to around 650-700 when the truck comes to a stop. I'm not sure if this is normal as I do not remember my previous manual tbi trucks doing this. I would like to fix this, so what should I be looking for or changing. Thanks.

 

[GoToGuy]

I would check throttle return springs, weak, missing? Then check wear on throttle body, throttle shaft sticking or massive vacuum leak? Remove throttle cable, cruise cable from throttle body. Any or high resistance, drag in cables lacking lube. That's a start since you have no service history, start at zero.

 

[Jebadiah]

I would check throttle return springs, weak, missing? Then check wear on throttle body, throttle shaft sticking or massive vacuum leak? Remove throttle cable, cruise cable from throttle body. Any or high resistance, drag in cables lacking lube. That's a start since you have no service history, start at zero.

Thanks for your input. I just got done checking for vacuum leaks and found the egr vacuum line was cracked so I deleted the egr system. Throttle moves freely and snaps shut as soon as you take your finger off the lever. Would a sucked tb gasket or worn throttle shaft cause this, or would it just idle high all the time?

 

[GoToGuy]

Removing throttle cable, and return springs then you can freely move shaft to check for wear, loose bushings.
I would have just replaced the vacuum line, left the EGR alone. Next I would hookup a scanner check all sensors and data. Refer to service manual about high idle, what else to check or test.

 

[Jebadiah]

Update: located problem. Temperature sensor for ecm (the one on top of the intake) was reading an inaccurate ohms value. Replaced the sensor, brought it up to operating temperature, idle dropped like a stone. I can now achieve smooth transitions between gears. Thanks guys!