The 2.5L was taking a long time to warm up. Also no reading on the air/fuel monitor which reads the voltage signal from the O2 sensor unless I would floor it.

Then the LED's on the A/F monitor to would cycle thru from no reading to lean to rich to lean to no reading. Meanwhile after about a minute the engine light would come on.

Later in the day when the temp was warmer everything worked fine above 30 mph. At low speed no reading on the A/F monitor and the engine light came on.

Used the Mighty Vac hand pump to check the vacuum motor on the air cleaner snorkle. Works great. Then checked the air charge temperature control valve in the base of the air cleaner when the engine was cold. It won't let vacuum pass thru, so I've got a replacement on order from NAPA.

Could a bad air charge temp. control valve cause Code 44 in cold weather?

No.......you would get that code from your temp sensor not the mat sensor. Mat would give you code 23.

Phil

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GTDude
OVER 25 years GM experience

the cts can really screw up the fuel system,but i dont know if that the problem.im more leaning toward the egr not sealing correctly.ive had the problem 2 times,once it was the egr and the other it was the throttle body gasket.i did have some fuel problems,and changing the cts helped alot to.
be careful if your still driving her,i burn't two valves while my fuel was messed up going lean.rich,lean,rich
hope i helped
shane

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I started the 84 database
so come on guys send me all the info you can get

I think he's talking about the thermo valve that opens/shuts the thermac door in the air cleaner neck. Not a MAT.

Thermac not working probably would not result in a lean code setting. It is used to prevent icing the 300 TBI. If it set a code at all, I think it would be rich mix due to ice resticting the air.

Note: it matters how that thermal valve is connected. if backwards, the door won't work and you have a vac leak.

First thing... if your AF meter is sharing the ECM's O2 sensor then disconnect it. You should not be sharing the O2 sensor. That alone can cause wierd problems. Not only can the meter load up the O2 sensor circuit, it can induce noise on it that the ECM can't handle.

Besides a bad CTS or O2 sensor. you could easily have wiring problems. Loose/dirty connectors are all it needs to act up. Go over all the grounds really good as well. Check every ground in the engine bay.

EGR and several other things could stick and leak when cold. Check everything.

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11-Sept-01, The day the world as we knew it ended.

quote theogre:I think he's talking about the thermo valve that opens/shuts the thermac door in the air cleaner neck. Not a MAT. First thing... if your AF meter is sharing the ECM's O2 sensor then disconnect it. You should not be sharing the O2 sensor. Besides a bad CTS or O2 sensor. you could easily have wiring problems. Loose/dirty connectors are all it needs to act up. EGR and several other things could stick and leak when cold.

BINGO! The thermo valve, not the MAT, is the correct part.

I have 2 switches on the dash, 1 to open the circuit between the O2 sensor and the Air/Fuel monitor and 1 to kill the 12 v power to the Air/Fuel monitor. I anticipated that it may cause a problem. I have put on over 2,000 miles at 30+mpg with no problems to the ECU.

Killing the O2 signal and the power has no effect. Then engine light stays on. The O2 sensor is fairly new as is the EGR valve.

The problem seems to be intermitent yet speed related.

Any further insights? I should have a new Thermac valve tomorrow morning.

disconnect the AF meter wire from the O2 completely. With it disconnected at the dash it is now a few meter long antena.

Beyond that... check the O2 sender wiring and the sender. Something is making it nuts.

also make sure the round connector that goes to the O2 sensor is actually making connection. That one takes a real beating and is fairly easy to wreck internally.

[This message has been edited by theogre (edited 12-23-2002).]

The O2 sensor is still putting out a voltage reading to the ECM. It's just a little lower than normal. Lower O2 voltage means the sensor is running a little cooler.

The hotter the O2 sensor the higher the voltage output. That's why went it's cold, the output is 0.0 volts.

O2 sensor disconnected with a warm engine gives 459 mv on the Scan Tool, connected it reads 4 to 8 mv with crosscounts runnning from 64 to 72.
I'll pull the O2 sensor and measure voltage generated when heated with a butane torch.

If it's good, it's starting to look like water in the combustion chamber. I just hope it's not another cracked head.

The problem was a slow responding MAP sensor.
It would generate the correct voltages, but there was about a 1 second lag between pressure change and voltage change.

A new MAP made the problem vanish!