Surging idle on cold start

1997 said:

from my search on possible causes for code 45:

This is the description of a Code 45 as set on GM products It is an indication of a rich mixture as indicated by the oxygen sensor readings.

Circuit description: The ECM supplies a voltage of about .45 volts between the appropriate terminals of the sensor. (If measured with a ten megohm DVM, this may read as low as .32 volt). The O2 sensor varies the voltage within a range of about one volt, if the exhaust is rich, down thru about .10 volt, if exhaust is lean.

The sensor is like an open circuit and produces no voltage, when it is below about 360 degrees C, 600 degreeF. An open sensor circuit, or a cold sensor, causes Open Loop operation.

Test description:

1.) Code 45 is set when the O2 sensor signal voltage remains above .7 volts for 30 seconds or more and in "closed loop".

2.) Engine time after start is one minute or more.

3.) Throttle position between 2 % and 20 %.



Diagnostic aides:

1.) The code 45 for rich exhaust is most likely caused by one or more of the following:

a. fuel pressure - system will go rich, if pressure is too high. The ECM can compensate for some increase. However, if it gets too high, a code 45 will be set.

b. Leaking injector or rich injector - perform an injector balance test. Check for fuel contamination in the oil..

HEI shielding - an open ground ckt 453 may result in EMI, will result in induced electrical "noise". The ECM looks at this noise as reference pulses. The additional pulses result in a higher than actual engine speed signal. The ECM then delivers too much fuel, causing the system to go rich. The engine tachometer will, also, show higher than actual engine speed, which can help in diagnosing this problem.

d. Canister purge - check for fuel saturation. If full of fuel, check canister control and hoses.

e. MAP sensor - an output that causes the ECM to sense a higher than normal manifold pressure (low vacuum) can cause the system to go rich. Disconnecting the MAP sensor will allow the ECM to set a fixed value for the MAP sensor. Replace the sensor if the rich condition goes away when the sensor is disconnected.

f. TPS - an intermittent TPS output will cause the system to go rich, due to a false indication of the engine accelerating.

g. O2 sensor contamination - Inspect oxygen sensor for silicone contamination from coolant, lead contamination from fuel or improper RTV sealant. Silicone contamination will be indicated by a Code 45 and lean drivability conditions and a powdery white deposit on the sensor. The ECM will then reduce the amount of fuel delivered to the engine causing a severe surge drivability problem.

Check for a leaking fuel pressure regulator by checking the vacuum line to the regulator. If there is fuel in the vacuum line, replace the regulator.

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Do the 1995's use the heated O2 sensors?

Donald Mitchell said:

Do the 1995's use the heated O2 sensors?

Click to expand...

yes, when equipped with the 4l60e.

1997 said:

back on the hunt to repair this.
unplugged CTS, won't start, set code 15, plugged back in.
unplugged 02 sensor, same issue, no code set, scanner reported no closed loop and 02 sensor reported RICH.

Does this sound right?

Click to expand...

I find it hard to look at O2 sensor output and be confident it’s ok. As I mentioned, my experience was one where the output of O2 was large enough, small enough but was falling out of closed loop due to other checks like time to react to change in AFR commanded by ECM. I don’t remember if you changed O2 but at this point if you can’t look at data logs to see why it’s bouncing in/out of closed loop it’s down to changing something and see if it helps. I’d change O2 sensors.

Id focus on why it can’t stay in closed loop when cool. Without looking at data at time of switch I don’t have a lot of ideas. Perhaps do some research to see if it’s in the correct AF cell at cold idle? Maybe some sensor input is putting it into wrong cell for conditions - like TPS, CTs, etc.
there are others with a lot more experience chasing things like this - maybe someone else has an idea.

thanks for your input, agreed its time to change something and see what happens.

its hard to get data because to keep it from stalling you have to rev it up etc, so lots of data changes on the scanner, even if things were operating correctly

i'll replace the 02 and update.

O2 sensor appears to have resolved my issue.
replaced with GM GENUINE AFS76, AC Delco.