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So I just finished flushing the coolant of my 3400 sfi Impala and both the code for the EGR and thermostat are on. I just bought this Impala for $500 and could the p0404 and p0128 be related? The radiator was disgusting when I flushed it, like the coolant was changed with tap water 15 years ago.

Is it most likely a fluke they came on together? I plan on deep cleaning the throttle body and running some seafoam in the intake. Already changed the oil, air filter, fuel filter and replaced a few lines. The car hasn't gotten to operating temperature since the flush and constantly running cold as well as it's running low idle almost to the point of stalling. Where should I start at?
 

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So I just finished flushing the coolant of my 3400 sfi Impala and both the code for the EGR and thermostat are on. I just bought this Impala for $500 and could the p0404 and p0128 be related? The radiator was disgusting when I flushed it, like the coolant was changed with tap water 15 years ago.

Is it most likely a fluke they came on together? I plan on deep cleaning the throttle body and running some seafoam in the intake. Already changed the oil, air filter, fuel filter and replaced a few lines. The car hasn't gotten to operating temperature since the flush and constantly running cold as well as it's running low idle almost to the point of stalling. Where should I start at?
My only thought linking the codes is that somehow, during the flush, water got to both devices and is affecting the signals from them to the engine computer. As I recall, the temp sensor is under the throttle body, and the EGR is just aft of it. Perhaps they share the same wiring harness?

Does the needle on the temp gauge climb any? Or is it stuck all the way down at the end?

Doug

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My only thought linking the codes is that somehow, during the flush, water got to both devices and is affecting the signals from them to the engine computer. As I recall, the temp sensor is under the throttle body, and the EGR is just aft of it. Perhaps they share the same wiring harness?

Does the needle on the temp gauge climb any? Or is it stuck all the way down at the end?

Doug

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Thanks Doug. They do share the same wiring harness and the temperature gauge needle will slowly go up to about a quarter, not even hot enough for the thermostat to open. The code is reading that the engine is operating at low temperatures, despite it being about 95-100 degrees F outside. I bought a new thermostat I'm going to put it on after I finish cleaning the EGR and throttle body. Even after 50 miles of interstate driving in 95 degree weather the car won't get even half way to operating temperature. The acceleration is slow, getting horrible gas mileage and the engine is knocking in low gear.
 

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Thanks Doug. They do share the same wiring harness and the temperature gauge needle will slowly go up to about a quarter, not even hot enough for the thermostat to open. The code is reading that the engine is operating at low temperatures, despite it being about 95-100 degrees F outside. I bought a new thermostat I'm going to put it on after I finish cleaning the EGR and throttle body. Even after 50 miles of interstate driving in 95 degree weather the car won't get even half way to operating temperature. The acceleration is slow, getting horrible gas mileage and the engine is knocking in low gear.
If the temp gauge is moving and appears to be working, my guess is you have a thermostat stuck open. So I think your plan to replace it is the right one.

Let us know what you find. Seems like the only ones I've ever seen stuck open are the fail safe type, which latch themselves permanently open if they get hot enough.

Doug

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