'86 C4 automatic..I installed an Airaid TBS, cleaned out the TB w/ carb cleaner & removed the MAF screens all for better aspiration. Upon startup, now I get a high idle of 900-1000, then idle settles down to 800 @ operating temp. Is there any explanation for the new high idle condition & how do I bring it down to specs, or is this normal ?? Thanks for any input..

 

Reset your base idle:

Here's how:

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 low 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 with throttle closed. I run mine at .63 volts for better throttle response
and still not changing the idle speed. No codes either.

You're done.

 

I follow you all the way to #8 TPS sensor; can you explain where it is & what it does??

 

Black thing ;pass side of TB .Has 3 wires coming out of it and is connected to the throttleshaft.
One of the main input devices to computer ; shows how much throttle you have,
hense Throttle Position Switch = TPS

 

great info, thanks!!

 

Indeed. Adjusted too high and the idle will go up. Do the procedure in the sequence provided. I "backprobe" the two top wires by making a small slit with a razor blade in the insulation. I poke the leads of my multi meter in there while TPS is still connected, since my weatherpack connector has a grommet seal on each wire that prevent me from inserting the lead directly from behind.

TPS circled in RED.

 

86Pacer: Excellent write up! I would add these additional comments on setting the base idle:

1. Make sure you time the engine (to factory spec) before doing the base idle process.
2. The engine should be at operating temp before doing the adjustment.
3. Make sure the AC is turned off while the adjustment is being performed.

Hope these comments are helpful

 

I made my own TPS voltage checker thing. I used some solid copper wiring and stuck it in the TPS and the other ends into the connector. Then I can just touch the copper with a meter to check voltage, no cutting of insulation required