1990 TBI 350 Warmup Idle Speed ?

[Bright Idea]

1990 350 TBI in V2500 Suburban. Recently it stopped the high idle on startup. This took place from one evening to the following morning. Makes me believe that this is a component failure ? It will start with just a touch of foot on the pedal and hold adequate idle until it warms up. Once warm it idles at what I would consider normal warm idle speed. It drives fine. No stall or hesitation and smooth thru the rpm range. I realize there can be numerous components involved in this. I have to believe this is a single component failure ? Is there a component involved in the signal to idle high when cold ? This is the only issue as far as I can tell. Hoping to hear from those of you with more experience with this system that I have. Thanks

 

[gmbellew]

not sure, but it is likely a component used to set open loop parameters. perhaps the CTS? you can check voltage with key on, but not started and convert voltage to temp and it should be close to the ambient air temp. high idle on start up seems more aggressive to me when it is colder....

 

[Bright Idea]

Thanks, I actually changed out the CTS asI had a problem previously involving it. I would agree that the colder the weather the higher the idle seemed to be. I will check the voltage of the CTS. This situation happened overnight, so it is my belief that it is a particular component, possibly a ground issue ?

 

[bucket]

Likely a failed idle air control valve. It could be a problem with the wiring on that circuit, but since it literally happened overnight, the valve itself would be suspect #1.

 

[bucket]

Oh, or simply a clogged passage for the IAC. A chunk of carbon buildup could have dislodged and blocked the port.

 

[Bright Idea]

Thanks, I will go after the IAC. This did happen after I changed out a failed kick down relay. I had taken it out on the highway and put it thru the paces a couple of times checking out the kick down function. Maybe I blew the carbon loose in the IAC ?

 

[fast 99]

Thanks, I will go after the IAC. This did happen after I changed out a failed kick down relay. I had taken it out on the highway and put it thru the paces a couple of times checking out the kick down function. Maybe I blew the carbon loose in the IAC ?

Or EGR

 

[Bright Idea]

I did replace EGR in recent past. No Check engine light and no codes. Would make sense that it is mechanical rather than electrical.