ok i have read almost every thread on here regarding this problem! urgh!! had a rat get under the hood last week chewed throught the #8 injector wires. ended up removing the TB and plenum to clean everything. also replaced the thermostat while i was at it because when it is 30 outside the car never got above 130 degrees when driving. anyway replaced the iac while i was at it. reset the idle to 400 with the car in drive. went to reset the tps voltage and it will not go above .36 even when it is turned all the way to the upper stop counter clockwise. checked the upper two wires black and blue. the original voltage was around .21 which seems to be where it likes it the best. .23 is where it is set at now with it in park it is at 800rpm. not sue where to go from here because it runs great. other than a air and heat problem. just blows out of all vents and defrost regardless of where it is set.
Jim
when it is at .36 the car is at 2700 rpm. which isnt good. the TB blades are shut all the way also. one of the screens below the windshield appeared to be chewed through so i guess i will be tearing the dash apart to figure out the heating problem.

Have you got 5V on one of the wires (IIRC gray )

good call! yes there is 5v on the gray wire. i had the voltmeter set on the wrong setting. when i couldnt get the right reading i double chkd the multimeter it was on dc mv instead of 10ohm where it should have been. stupid me!!
you figure after twenty years working on apache's i could figured that out!
JIM

Correct value at idle is 0.53V - 0.55V, because I was never able to hit the suggested 0.54V

As for the air blowing out only the vents; it's most likely a bad vacuum source, there are many messages on the subject here if you do a search or two, usually a pretty easy fix.

Unless you're not lucky and it's the electronic controller, that's not so easy or cheap...do you have the manual or electronic climate controls?

electric control. just havent had a chance to dig into it. i did spend some time today looking for the vacume line that runs through the fire wall and couldnt find anything that was sucking air. i'll search the forum for the wiring and vacume diagram. thanks for everyone's help as usual.
JIM

Here's a "how to set" on base idle, tps & IAC. This one is a bit wordy but its what I have on this computer.

Technical Information Bulletin Rev. B 5-31-04

How to Adjust your Early C4 TPS and Idle Speed
by Lars Grimsrud
Colorado Corvette Crazies (CCC)

The Ultimate Corvette Tuning & Beer Drinking Fraternity
Lafayette, CO

This tech paper will discuss the procedure for correct adjustment of the Minimum Idle Speed and for adjustment of the Throttle
Position Switch (TPS) on the early C4 Corvette TPI systems. These steps apply specifically to the 1985 model year, and in
general to other years. Later model years do not have adjustable TPS’s.
NOTE:
The Minimum Idle Speed sequence outlined in this paper is taken directly from the 1985 and 1986 GM Corvette Service
Manuals with some clarifications and simplifications added by me. Be aware that there are aftermarket manuals that outline a
different sequence. I have used the sequence in this paper and verified that it is correct for the model years noted. You may
choose to use the procedural sequence outlined and recommended by others.
General
Idle speed and off-idle throttle response on the early TPI systems is determined by correct adjustment of the minimum idle speed
screw combined with a correct setting of the TPS. I’ve seen many of these cars that have had their idle speed “corrected” by
well-intentioned mechanics and owners by simply screwing the minimum idle speed screw in a few turns. This really messes up
the settings, and will not make your car perform properly. Doing a correct setup of the TPS is one of the easiest ways to make
your car feel and respond better. To maximize the benefit of this procedure, I recommend that you first remove your Throttle
Body (TB), disassemble it (it’s incredible easy – there are a total of about 5 pieces in it…), clean the TB up really good with
some spray carb cleaner, and put it back together. A nice clean TB will really put an edge on the performance improvement you
will get by doing this procedure.
NOTE: If you disassemble and clean your Throttle Body, including removal and cleaning of the IAC, it is recommended that
you measure the extended length (protrusion) of the IAC “tip” before you re-install the IAC. If the “tip,” or “needle” of the IAC
(referred to correctly as the “Pintle”), is extending out too far, you will jam it into the seat and damage it during re-installation.
So before you install the IAC, measure the distance from the very tip of the Pintle to the surface of the IAC body that the gasket
seats against (with the gasket removed). The distance should be 28mm (1-1/8”) or less. If the distance is greater than this, you
must retract the Pintle into the IAC Body. There are two different styles of IACs:
If your IAC has a “collar” around the electrical connector end, simply push on the Pintle with firm hand pressure while rocking it
slightly side-to-side until it retracts.
If your IAC does not have a “collar,” compress the Pintle Retaining Spring towards the body of the IAC and try turning the
Pintle clockwise as seen from the Pintle end of the IAC. If it turns, keep turning until it retracts to the 28mm position. Then,
return the spring to its original position, with the straight part of the spring end lined up with the flat surface under the Pintle
head. If, however, the Pintle does not turn, use firm hand pressure as described above to retract it.
Once set up, install the IAC with the gasket and torque to 13 ft-lbs.
The Service Manual has instructions for doing the following operations, but the directions are scattered through several sections
of the Manual. Here is the complete, step-by-step process for doing this (not including TB rebuild). All specs and steps are taken
directly from the Manual (all 3 different sections), and this process is absolutely correct.
Tools & Equipment
You will need the following tools and equipment:
1. A set of Torx wrenches. You can buy a complete set in a nice, genuine plastic pouch at Sears.
2. A good digital voltmeter that will read voltages less than 1 volt.
3. A paper clip.
4. A small screwdriver.
Procedure
There are two electrical components on the TB that you will be working with: The TPS and the Idle Air Control Valve (IAC).
Make sure that the connectors for these two components are easily accessible and that you can easily disconnect the IAC.
You will also be playing with the diagnostic connector under the dash. Remove the cover (if it’s still in place). Bend your paper
clip into a “U” shape. You will be playing with the two top right hand terminals (“A” and “B”) in the connector.
• First step is to set the minimum idle speed. If nobody has messed with this on your car before, the set screw will be covered
by a pressed-in plug. It’s located on the driver’s side of the TB. Remove this plug if it’s there.
• With the IAC connected and the ignition “OFF,” stick the paper clip into the diagnostic connector from “A” to “B.” This
grounds the diagnostic lead.
• Turn the ignition to the “ON” position without starting the engine. Wait 30 seconds.
• Now, with the ignition still in the “ON” position, disconnect the IAC connector at the IAC.
• Remove the paper clip from the diagnostic connector.
• Start the engine and allow it to reach normal operating temperature. The idle speed will probably be really low, and you
may have to coax the engine a bit with the gas pedal to keep it running for a while.
• If your car is an automatic, set the parking brake and put the transmission in “DRIVE.” If your car is a manual, leave it in
neutral.
• Adjust the idle speed screw to obtain 400 rpm in drive or 450 in neutral.
• Shut off the engine and re-connect the IAC.
NOTE: Some later year GM Shop Manuals recommend disconnecting the distributor ECM wire (“Timing Connector”) near the
brake booster. This will prevent the ECM from altering timing – and idle rpm – during the rpm adjustment. Early GM Manuals
do not contain this step. If you disconnect the timing connector, you will get a Code 42 stored in the memory of the ECM. The
memory must be cleared of this code after re-connecting the timing connector.
That’s it for idle speed. Now on to the TPS.
There are 3 wires stacked vertically on the TPS. You will need to be able to measure the voltage between the two top wires.
You can either buy a special harness connector that breaks these wires out (from Mid America), or gently pierce the insulation of
the wires with the pointy prongs on your volt meter. You can also stick a paper clip into each of the two top locations of the
connector and clamp onto the paper clips to measure the voltage. Whatever is easiest for you.
• Turn the ignition to the “ON” position without starting the engine.
• Loosen the TPS Torx adjustment screws.
• Set your volt meter to a low scale DC volt setting that will accurately read less than 1 volt.
• Measure the voltage between the two top TPS wires.
• Adjust the TPS by rotating its position until you get a reading of .54 volts.
• Tighten the Torx screws and recheck the voltage. Re-adjust if necessary to make sure voltage is right at .54.
• Turn the ignition “OFF.”
You are now in perfect adjustment on idle speed and TPS output. Start the engine. It may take a few seconds for the car to
“catch on” to its new settings.
Questions, Comments & Technical Assistance
If you have questions or comments regarding this article, or if you notice any errors that need to be corrected (which is quite
possible since I’m writing this from memory…), please feel free to drop me an e-mail. Also, if you need any technical assistance
or advice regarding this process, or other maintenance issues, feel free to contact me: V8FastCars@msn.com

Quote:

Here's more or less what you're looking for under the hood, yours may not be in this exact location but the setup is the same, check valve needs to be there and vacuum hoses hooked up right.

Attach file:

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  vacuumvalveLarge.jpg (67.00 KB)

my ck valve is actually next to the fire wall. when i had it running last night and shut it off i started messing with the vacum line i found a spot in the hose when bent a little hissed pretty good. ill put the ck valve where it goes and replace the vacum wire today. it was around 0100 when i was messing with it so ill get back on it today. thanks for the pic and help.
JIM

Quote:


[IMG]http://i171.photobucket.com/albums/u309/vetteoz/electrical/checkvalve.jpg[/IMG]


Rear port to HVAC inside ; side port to cruise and vac ball under headlight
Be very careful with plastic HVAC hardline to the wiring harness behind dist .
Becomes brittle and commonly breaks off flush with the harness requiring opening of harness up to get a clean end
.

replaced the ck valve today. when i disconnected the hvac line it hissed pretty loud so i am pretty sure the vacuum is good. after i bought the car i had the dash apart to find a rattle and discovered the ac control unit looked like someone had poured a 44oz red slushie into it. cleaned it and put a new cover plate on it because the old one was faded and the clearcoat was almost gone. i really never ck the operation of the defrost and heater because it was summer. so it might just be that the board in it is tweaked. the only thing that doesnt apperar to work on it is the outside temp button. all other functions operate other than where the air comes out from. does anybody have the diagram of the vacuum lines under the dash. thanks for everybody's help. i kept the ck vave in the location as in the picture above.
JIM