IAC Solenoid...

'88 GMC Suburban 4x4 5.7 TH700
How do I check if my IAC solenoid is working?

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You don't have an IAC solenoid, just an electronic IAC valve. Is the vehicle idling poorly?
Doc
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Yup, and idling hi, and hard to start unless I give it a little bit of throttle opening...
| > '88 GMC Suburban 4x4 5.7 TH700 | > | > How do I check if my IAC solenoid is working? | | You don't have an IAC solenoid, just an electronic IAC valve. Is the | vehicle idling poorly? | | Doc | | |
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How and when does the valve work? Is it either open or closed or does it vary or oscillate? Does it function only when cranking or idling or with revs?
| > '88 GMC Suburban 4x4 5.7 TH700 | > | > How do I check if my IAC solenoid is working? | | You don't have an IAC solenoid, just an electronic IAC valve. Is the | vehicle idling poorly? | | Doc | | |
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it vary or oscillate? Does it function

Ok, with carbs, the primary throttle plates are always cracked just a wee bit (varies with where the idle stop screw is set) and that's how the air gets into the idle mixture. With the TBI motors the throttle plates are more or less shut when your foot isn't on the go pedal, and the primary way the air gets into the mixture is via the IAC valve. The valve has a pintle which moves in and out that varies the amount of air allowed thru a passage that bypasses the throttle plates. Idle speed doesn't change (aside from open/closed loop and A/C on/off), but the pintle position varies with how much air she needs to idle correctly based on engine temp, A/C load, etc.
It functions during cranking and idle. As soon as the TPS picks up off-idle throttle position, the IAC is no longer in the mixture process. I'll be honest, I've never seen one completely fail; seen one gummed up pretty bad which inhibited pintle movement, but never seen one die altogether. I think your problem may lie elsewhere.
If you have to crack the throttle to start it, it means there is too much gas or not enough air in the mixture. Likely too much gas. The fact that it idles high also suggests too much gas (or too much air, which the ECM compensates for by dumping more gas in the mixture). My suggestions:
1) Yank the IAC and give her a good hosing with TB cleaner to remove any gum deposits. Don't use carb cleaner. 2) Run a resistance check on the CTS to see if it's cooked (more likely) and telling the engine it's bloody cold hence dumping the gasoline into the motor. E-mail me gmc <underscore> man <at> adelphia <dot> net and I'll send you a chart of CTS temps/resistance values. 3) Fuel Pressure regulator may be shot, allowing too much fuel feed to the injectors 4) Could be a simple vacuum leak mucking the whole works up! What her vacuum at idle?
Doc
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E-Mail didnt work, Doc!
First off...CTS??? What is it and where is it?
As for the throttle plates being closed, they aren't! They aren't open allot, but they are open about as much as a carbs would be...well, a bit less. I can pull the linkage and the plates close minutely and the idle drops ever so slightly. I couldn't find anything that remotely resembled a vacuum leak, and the IAC valve wasn't all that bad(I did clean it up anyway). I am running a good dose of SeaFoam through the gas and oil to hopefully help. I also have a, not really hesitation, more like a 'wind up', when I goose it a bit. When idling, if I give her some throttle and let off, she rolls down slowly from a very high idle down to the 'normal' current high idle.
Have I confused you yet? This is the newest vehicle I have owned and the first with fuel injection.
Vacuum is a fairly steady 20hg when cold. High? Low? I am gonna do a full tune up, plugs, wires, cap, rotor... Hopefully that will at least help.
Anything else you could suggest would be greatly appreciated.
| > How and when does the valve work? Is it either open or closed or does | it vary or oscillate? Does it function | > only when cranking or idling or with revs? | | Ok, with carbs, the primary throttle plates are always cracked just a wee | bit (varies with where the idle stop screw is set) and that's how the air | gets into the idle mixture. With the TBI motors the throttle plates are | more or less shut when your foot isn't on the go pedal, and the primary way | the air gets into the mixture is via the IAC valve. The valve has a pintle | which moves in and out that varies the amount of air allowed thru a passage | that bypasses the throttle plates. Idle speed doesn't change (aside from | open/closed loop and A/C on/off), but the pintle position varies with how | much air she needs to idle correctly based on engine temp, A/C load, etc. | | It functions during cranking and idle. As soon as the TPS picks up off-idle | throttle position, the IAC is no longer in the mixture process. I'll be | honest, I've never seen one completely fail; seen one gummed up pretty bad | which inhibited pintle movement, but never seen one die altogether. I think | your problem may lie elsewhere. | | If you have to crack the throttle to start it, it means there is too much | gas or not enough air in the mixture. Likely too much gas. The fact that | it idles high also suggests too much gas (or too much air, which the ECM | compensates for by dumping more gas in the mixture). My suggestions: | | 1) Yank the IAC and give her a good hosing with TB cleaner to remove any | gum deposits. Don't use carb cleaner. | 2) Run a resistance check on the CTS to see if it's cooked (more likely) | and telling the engine it's bloody cold hence dumping the gasoline into the | motor. E-mail me gmc <underscore> man <at> adelphia <dot> net and I'll send | you a chart of CTS temps/resistance values. | 3) Fuel Pressure regulator may be shot, allowing too much fuel feed to the | injectors | 4) Could be a simple vacuum leak mucking the whole works up! What her | vacuum at idle? | | Doc | |
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Inline......................

Ya must have got it wrong, cause I wrote it down right! gmc <underscore> man <at> adelphia <dot> net

Coolant Temperature Sensor, tells the ECM how warm or cold the engine is and usues the reading to adjust fuel mixture, timing, etc. Located just beside the waterneck, will have two wires running to it, yellow and black. When they crap out they default to read -40* which runs a really rich mixture.

allot, but they are open about as

the plates close minutely and the idle

vacuum leak, and the IAC valve

SeaFoam through the gas and oil to

up', when I goose it a bit. When

from a very high idle down to the

That sucker have cruise control? If so, check the adjustment on the cruise control throttle linkage and make sure it isn't holding it off-stop.

the first with fuel injection.
Nah, not yet anyways.

full tune up, plugs, wires, cap,

20 inches is about normal. Tune up might help, might be the source of yer' problems to begin with.

E-mail me so I can send you that chart so you can ohm-out the CTS.
Doc
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