[Gmecm] 454 TBI 1988 suburban

Sun Mar 27 05:55:43 UTC 2005

Sorry about the following book report but it should explain a lot.

It looks like you already have it figured out but this info should be very
helpful in the future.  If the IAC did not fix it I would have suggested a
temp. sensor.  Have seen more than one out of range causing an out of spec.
high idle.

Even though all reference material always will say a TPS is not adjustable,
many are, or can be made to adjust.  Actually to get the maximum performance
from a computer controlled engine you want to adjust the TPS to a maximum as
close to 5 volts wide open throttle as possible.    

Throttle Body Injection 

1. Remove air cleaner and gasket. Plug TBI vacuum port for THERMAC
(Thermostatic Air Cleaner). With Idle Air Control (IAC) valve connected,
ground diagnostic "test" terminal of ALDL connector (jumper terminal "A" to
"B"). 

2. Turn ignition switch to "ON" position, DO NOT start engine. Wait
approximately 30 seconds for IAC valve pintle to extend and seat in throttle
body.

IDLE AIR CONTROL

(IAC) MOTOR MINIMUM IDLE SPEED Throttle Body Injection 

1. Remove air cleaner and gasket. Plug TBI vacuum port for THERMAC
(Thermostatic Air Cleaner). With Idle Air Control (IAC) valve connected,
ground diagnostic "test" terminal of ALDL connector (jumper terminal "A" to
"B").

2. Turn ignition switch to "ON" position, DO NOT start engine. Wait
approximately 30 seconds for IAC valve pintle to extend and seat in throttle
body.

NOTE: Minimum idle adjustment is necessary only when throttle body assembly
has been replaced.

3. With ignition on, disconnect IAC valve electrical connector. Remove
ground at ALDL "test" terminal. Start engine and check minimum idle speed.
Adjust to specification, if necessary. 

4. Turn ignition off. Using an awl, remove plug for minimum idle speed
adjustment by piercing, then applying leverage. Start engine. Adjust idle
screw to specification. Turn ignition off. Reconnect IAC valve electrical
connector. Install air cleaner and gasket. THROTTLE BODY MINIMUM IDLE SPEED
(RPM) 

TPS OUTPUT VOLTAGE CHECK 

Throttle Body Injection 

Connect digital voltmeter between TPS connector terminals "A" and "B" using
jumper wires. With ignition on and engine off, TPS voltage should be less
than 1.25 volts. Replace TPS if voltage is more than 1.25 volts. Before
replacing TPS, ensure minimum idle speed is set correctly.

Application:

Man. Trans. 

Auto. Trans. 

All Engines 600-650 

(1) 500-550 

(1) Adjustment is made with transmission in Drive.

NOTE:                         

Throttle

Position Sensor (TPS) on fuel

injected models is not adjustable.

Coolant Temperature Sensor 

(CTS) The CTS, a thermistor that changes value based upon temperature, is
located in a coolant passage.

The ECM sends a 5-volt signal to the CTS through a resistor in the ECM. This
5-volt signal is reduced by the resistance of the CTS and a return signal is
sent to the ECM. When coolant temperatures are low, CTS resistance is high
(1000,000 ohms at -40?F/-40?C)). When coolant temperatures are high, CTS
resistance is low (70 ohms at 266?F/130?F). Engine coolant temperature is
used by the ECM to control most CCC systems. A coolant sensor problem may
set Code 14 or 15.

-----Original Message-----
From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org] On Behalf
Of jason34
Sent: Wednesday, February 16, 2005 9:14 AM
To: gmecm at diy-efi.org
Subject: RE: [Gmecm] 454 TBI 1988 suburban

 Thanks for the info. Is that rpm when its in gear with auto.After I wrote

that email I went and put the new air idle speed motor in and the idle stays

at 950 in park and does'nt go up and down like it was. Runs at 650 in park.

JASON

-----Original Message-----

From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org]On Behalf

Of David Cooley

Sent: Saturday, March 26, 2005 8:03 PM

To: gmecm at diy-efi.org

Subject: RE: [Gmecm] 454 TBI 1988 suburban

somewhere between 650-750

if it has a code for tps too low, the idle will be bumped up.

I'd check the TPS... voltage should be between .5-.75V at idle

________________________________

        From: gmecm-bounces at diy-efi.org [mailto:gmecm-bounces at diy-efi.org]

On Behalf Of jason34

        Sent: Wednesday, February 16, 2005 10:14 AM

        To: gmc tbi

        Subject: [Gmecm] 454 TBI 1988 suburban

        Hi does any one know what the idle rpm should be ? I put a 4 wire o2

sensor in my truck. Now the idle isn't right it seems to fast.I also have a

fault code for the tps being to low. I can't seem to figure whats wrong.I

have A link plus to look up codes and info from computer. If anyone can help

with info that would be great. JASON

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