High cold idle

[Burban1990]

My 350 runs great but I feel the cold idle runs a little too high. I understand it's supposed to be that way while it's cold but it's a little too high. What's the best way to lower the idle for when it's cold on a throttle body? When it's warm it's fine.

 

[1987 GMC Jimmy]

Try to do an IACV relearn before doing anything and see if that does anything. You jump the A/B diagnostic terminals, key on, wait 45 seconds, unplug the IACV connector, key off, jumper out, replug the IACV. You can also (gently) clean the carbon off the valve pintle and check for carbon packed in the idle passages underneath. If that doesn’t work, expect that you have a cold vacuum leak that’s sealing itself a little when you get warm. Possibly base gasket or throttle shaft has worn into the TB, which would require a bushing to be installed. If the vehicle has more than 150-175K miles, it’s getting worn already. Cold and hot vac readings would be helpful to check for disparate values. You can check base timing, but I’d do that later, and only replace the IACV when you’ve exhausted all alternative.

 

[Vbb199]

Temp sensor or IAC faulty

Replacing Iac will require relearning idle by setting it manualy

 

[1987 GMC Jimmy]

^^^ CTS is another. I’d want to see serial data to see if the sensor was sending back actual temp confirmed by a temp gun at the sensor site. That’s fifteen dollars that I’d rather not waste if you don’t have to. You could also see IAC counts. Most people don’t want to make the scan cable, and while it’s cheap insurance to replace the CTS, I hate to throw away a good GM part (assuming original) for China’s finest.

 

[Burban1990]

Try to do an IACV relearn before doing anything and see if that does anything. You jump the A/B diagnostic terminals, key on, wait 45 seconds, unplug the IACV connector, key off, jumper out, replug the IACV. You can also (gently) clean the carbon off the valve pintle and check for carbon packed in the idle passages underneath. If that doesn’t work, expect that you have a cold vacuum leak that’s sealing itself a little when you get warm. Possibly base gasket or throttle shaft has worn into the TB, which would require a bushing to be installed. If the vehicle has more than 150-175K miles, it’s getting worn already. Cold and hot vac readings would be helpful to check for disparate values. You can check base timing, but I’d do that later, and only replace the IACV when you’ve exhausted all alternative.

Thank you for the response I just want to make sure this is the correct diagnostics terminal for my truck.

You must be registered for see images attach

 

[Vbb199]

Thank you for the response I just want to make sure this is the correct diagnostics terminal for my truck.

You must be registered for see images attach

Yes

 

[Burban1990]

One more quick question when the idle is high when you first start the engine being cold at what temperature does the idol drop down to normal?

 

[gmbellew]

for a 350 TBI, I'd recommend getting a bluetooth aldl reader and the aldldroid app. it lets you see what all the sensors see, for an all in cost of about $100. I can send you the file I found to use on my 1990 burb with aldldroid.

 

[Burban1990]

for a 350 TBI, I'd recommend getting a bluetooth aldl reader and the aldldroid app. it lets you see what all the sensors see, for an all in cost of about $100. I can send you the file I found to use on my 1990 burb with aldldroid.

Can you send me a link to the Bluetooth aldl reader? I'm not sure what I'm looking for. Is it made by red devil River?

 

[1987 GMC Jimmy]

One more quick question when the idle is high when you first start the engine being cold at what temperature does the idol drop down to normal?

Idle speed should begin dropping within a few seconds of startup, but I’ve never timed how long it takes to settle to about forty counts just sitting there.

 

[Burban1990]

Idle speed should begin dropping within a few seconds of startup, but I’ve never timed how long it takes to settle to about forty counts just sitting there.

That's what I kind of figured
My high idle lasts for much longer at least until I put it into gear. I try to let it warm up so it doesn't slam into gear when going into drive or reverse.

 

[fast68chevy]

CTS most likely is reading bad wrong.. you can test it with a simple multitester. there is a chart all over the internet that shows resistance measurement at certain temps, for these CTS, they do fail and can go innacurate. they dont last or work for forever. ive had to replace many,. im pretty sure its higher temp lower resistance. the ECM sees resistance value and converts that value to a temperature. a certain value is a certain temp. which determines fuel and idle speed and etc. combined with other sensors as well. and CEL codes 14 and 15 are CTS ones. thats one flash and 4 or 5 flashes, of the CEL lamp, in CEL lamp/ECM diagnostic mode, at the ALDL connectors

 

[Burban1990]

CTS most likely is reading bad wrong.. you can test it with a simple multitester. there is a chart all over the internet that shows resistance measurement at certain temps, for these CTS, they do fail and can go innacurate. they dont last or work for forever. ive had to replace many,. im pretty sure its higher temp lower resistance. the ECM sees resistance value and converts that value to a temperature. a certain value is a certain temp. which determines fuel and idle speed and etc. combined with other sensors as well. and CEL codes 14 and 15 are CTS ones. thats one flash and 4 or 5 flashes, of the CEL lamp, in CEL lamp/ECM diagnostic mode, at the ALDL connectors

Yeah that feels right because computer not getting correct temp readings and continue at higher idle. Thanks for the heads up. Gonna due a reboot first as suggested and if no success will move on to this.

 

[WFO]

Dang!

It sure takes a lot of stuff after 1986 to replace a flathead screwdriver.

 

[gmbellew]

Can you send me a link to the Bluetooth aldl reader? I'm not sure what I'm looking for. Is it made by red devil River?

i bought my aldl reader from http://www.1320electronics.com. but red river is probably ok also.