1989 Chevy K1500 — cuts out under loaf … power washed engine, covered carb & electricals w plastic.

Afterward, check engine light came solidly on. Checked codes, 22 & 33 — truck bogs on the freeway under load.

Checked all connections, seem fine. Reset check engine light (disconnect battery, touched positive and negative cables together).

Light was out, drives fine.

Now, engine light flickers now and then, will sometimes come on solid after start, but goes out after 5 mins or so … sometimes less, sometimes more.

Took it up steep roadway, cuts out under load, catches again when rpms drop.

This is an old mountain truck — not wanting to start replacing parts w no need.

But of course, engine light drives me batty, and don’t want to ignore potential big problem(s).

Any thoughts to diagnose or resolve?

 

The TPS & MAP sensor both receive a 5 volt reference signal from the ECM on a dedicated circuit. With the engine running or key on, engine off, check for 4.5 - 5.5 volts on the gray wire at each sensor connector. Note that if the engine is running you’ll need to back probe the connectors.

While watching the meter, wiggle test the harness between the TPS/MAP sensor and the lower passenger side of the firewall where the wires pass into the cabin. If the signal drops or cuts out completely in a given spot, open the harness for closer inspection and repair.

The reference signal is only shared between the TPS and MAP sensors - the likely problem is the splice in the harness where the circuit branches off to each sensor.

If the reference circuit is OK, check the TPS first as it’s operation has the most direct influence on ECM calculation and logic and the MAP code may only be setting because of the TPS.

Disconnect the TPS and Connect an ohm meter between the TPS terminals that correspond with the gray and dark green wires. Slowly open the throttle plate by hand and watch for a sudden drop or spike in resistance - an analog meter works best if you have one. Make sure to open the throttle all the way, then slowly close it as well.

Any sudden changes in resistance indicates the TPS is faulty and should be replaced.

 

GM OBD I Code 22:
Indicates that the Throttle Position Sensor (TPS)is reading abnormally low. TPS volts should be close to 0.42 V at closed throttle and rise smoothly in about 0.02 volt increments to a maximum reading of about 4.85 volts at WOT.

Typical causes for this code include:

1) Maladjusted TPS
2) Defective TPS
3) No +5 volt reference to TPS
4) TPS-return to ECM is shorted to ground or to sensor ground
5) Defective ECM

NOTE: The TPS must be adjusted to about 0.42 volts at closed throttle for the ECM to auto-zero properly. If necessary, adjust the TPS to bring the voltage up or down to this value at closed throttle.


GM OBD I code 23:
A disconnected Intake Air Temperature sensor is the most common cause of a code 23. Sensors are often unplugged when checking the air cleaner. If they are not reconnected, code 23 will set.
A quick test for the intake air temperature sensor circuit from the ECM would be to unplug the temp sensor and watch the intake air temperature sensor reading on the scan tool while jumping the harness side of the sensor connector. The scan readings should switch from full cold to full hot when inserting and removing the jumper from the connector.

I hope this information helps you out, billingstitan.