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
| 4) Could be a simple vacuum leak mucking the whole works up! What her
| vacuum at idle?