No high idle on cold start up

[Desert Rider]

My truck is a

1993 chevy 3500 with TBI and 4L80E trans. 150K Mi.

 

I have 2 problems

1. I can not get a check engine lite or codes for any prob. even when I disconect things on the motor

 

2. the engine does not idle up when cold. I have to give it a little throtle to get it to start and then it idles at about 700 as indicated on stock tac. witch is normal for when engine is hot.

 

Any info will be greatly appreciated

 

Scott

[GM-Tech]

Does the check engine light EVER come on? Such as when you just turn the key on without starting it?

 

Will it flash at least a code 12?

[Desert Rider]

Does the check engine light EVER come on?  Such as when you just turn the key on without starting it?

 

Will it flash at least a code 12?

 

<{POST_SNAPBACK}>

 

 

 

 

Yes I get the engine light when I turn on the key. and when I jump the two leads to read coads I get the code 12 continusly. sorry I should have included this info the first time

 

Desert Rider

[GM-Tech]

Possible bad idle air control valve for the lack of high idle on startup.

[Desert Rider]

Possible bad idle air control valve for the lack of high idle on startup.

 

<{POST_SNAPBACK}>

 

 

 

I looked at the IAC valve through the port in the throtle body and had my son put the truck in and out of gear, it appeared to be working and controled the idle ok. I was under the impresion that this would not happen if the IAC was bad?

 

Desert Rider

[GM-Tech]

I looked at the IAC valve through the port in the throtle body and had my son put the truck in and out of gear, it appeared to be working and controled the idle ok. I was under the impresion that this would not happen if the IAC was bad?

 

But is it capable of moving enough. When you shut the truck off, the IAC should retract fully in preparation for the next start. Does it? Shut the truck off and then look down the port. Can you see the pintle still protruding into the hole?

 

Been quite some time since I looked down into a TBI, but I believe that if anything, you might be able see just the tip of the pintle, if that.

[Desert Rider]

I looked at the IAC valve through the port in the throtle body and had my son put the truck in and out of gear, it appeared to be working and controled the idle ok. I was under the impresion that this would not happen if the IAC was bad?

 

But is it capable of moving enough. When you shut the truck off, the IAC should retract fully in preparation for the next start. Does it? Shut the truck off and then look down the port. Can you see the pintle still protruding into the hole?

 

Been quite some time since I looked down into a TBI, but I believe that if anything, you might be able see just the tip of the pintle, if that.

 

<{POST_SNAPBACK}>

 

 

 

 

I checked out the IAC and that was the problem. It was only moving about .040 to .050, Just barly enough to keep the engine from stalling when put in gear but not retracting properly as you said.

 

Thank you

Desert Rider