armybyrd

Just replace the idle air control valve and cleaned out my tb in my '88 C4 which fixed my stalling out condition, but tonight while driving I noticed at times the idle would be a bit high-around 1200-1400 and and the rpms seemed a lil high when I shifted(4+3). Though if I tapped the gas they would go back down to 8-900 at idle. Should I just check the throttle linkage or clean it? Any suggestions?

86PACER

Remove air duct and check throttle body blades and linkage for binding both by hand and by pedal.

Did you reset your base idle after doing so?

Check the voltage setting of your TPS sensor. Factory setting is .54 volts closed (idle). I run mine at about .63 before it affects the idle speed. This give me better throttle response. Much above that raises the idle speed. To check, backprobe the upper two TPS wires with key on and check voltage. Meter needs to be set to the 20K scale. Engine does not need to be on. Loosen the two torx screws and adjust.

armybyrd

How do you reset base idle?
By "backprobe" do you mean touch the upper 2 wires with the two ends that are connected to the meter?

86PACER

Yes, while the TPS is still connected hence "backprobe". I made two small slits with a razor blade in the wire insulation.
I just poke the tips of my multi meter leads through the slits to take a reading.

Before setting minimum idle speed, you need to unplug your EST connector. The same one you unplug when setting timing. This one:




1.Jump a wire or paper clip between the A and B terminals of the ALDL connector under dash as follows:




2. Turn ignition on but don't start the engine. Wait at least 30 seconds. During this time the IAC is resetting itself and if you get close you can hear it.

3. Go unplug IAC with ignition still on.

4. Start the motor and let it come to operating temps or closed loop. If RPMs are too low and engine wants to die, tighten the TB idle screw enough to keep it alive.

5. Remove the ALDL jumper wire or paper clip.

6. Now use a torx bit and adjust the idle speed to 400RPM in Drive for an automatic (Use your e-brake or an
assistant obviously), or 450 RPM in neutral for a manual car by turning the idle screw. It's located on the top corner of the TB.
Start with a high idle and work down so the motor does not die on you. If you start at lower RPMs and go up,
you'll have to try to keep the engine alive. So this is why it's better to start high and go down instead.

7. Turn the car off and reconnect your IAC and EST.

8. Now adjust your TPS sensor. Again, backprobe the top two wires with a multi meter on the 20K voltage scale
with ignition key on. Motor does not need to be running. Adjust by loosening the two torx screws and moving the
TPS by hand. Re tighten when in spec. Factory setting is .54 volts.

You're done.

RRT vette

Follow the instructions and check the linkage. It should fix the problem.

87 rag

My throttle body blades were hanging up a couple of years ago.
I sprayed some graphite on it where the blade axle rubs on the throttle body housing and it solved the problem.

I'm not saying you don't need to reset your IAC and TPS but your throttle symptoms are identical to mine, which the graphite cured.
You may have a couple of issues. I would do the graphite first so the blades are moving smoothly when you set the others.

Biker

I agree with the post above which recommends lubricant. Apply lubricant to the return spring, too, and make sure the spring is working properly.

beaver believer

20 thousand volts scale? Sounds like you're setting up to measure resistance(ohms). If I was wanting to measure less than 1 volt, I would expect to set the meter to its lowest scale.

86PACER

Correction, set to 20 scale not 20K.

beaver believer

I had printed out and did the TPS adjustment from a post from another forum, I think. The steps were very close to what you have posted but with a couple of differences. It said nothing about unplugging the EST connector and didn't have me starting the motor with the ALDL still jumpered. In fact, I seem to remember reading somewhere that one shouldn't start the motor with it jumpered. Now I wonder which is correct.

86PACER

What I gave you is exactly what the GM shop manual will also tell you. The shop manual was written by Gordon Killebrew. Perhaps the most knoledgeable person regarding C4's on earth.

MagicDragon

http://forums.corvetteforum.com/show....php?t=1968939 Check it out vettebyrd- same problem. I plan on removing, cleaning and lubing with graphite grease. I'll probably use a little compressed air to blow the grease into the housing shaft hole from the thorttle plate side.

87 rag

I wouldn't use grease. It will attract dirt and end up being worse in no time.
I used a dry graphite spray. It also works great on locks.

MagicDragon

Thanks 87 rag!!! I'll look for some at the local parts store today.

87 rag

Nice looking car!!