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2003 gmc envoy: liter..coolant temp sensor..stalls..stop lights

Resolved Question:

2003 gmc envoy. straight 6. 4.2 liter vortec. originally had a code saying bad coolant temp sensor, and stalls while at stop lights, and when light throttle is given. replaced temp. sensor. check engine light still on, no change in symptoms
Submitted: 7 years ago.
Category: GM
Expert:  MPMoore replied 7 years ago.
What is the code stored, a p0128? What is your idle speed when in gear?
MPMoore and 6 other GM Specialists are ready to help you
Customer: replied 7 years ago.
idle speed surges while in gear and in park. when cold the idle speed in park is around 1000 and about 800 toXXXXX once warmed up, the idle speed becomes about 600-700 in both park and drive. i used my scantool and noticed another code came along with it. P0128 and P0340.
Expert:  MPMoore replied 7 years ago.
OK, the p0128 is not a engine coolant temp sensor code. This code means that the engine is not warming up to running temp within a spec time. basically this means your thermostat is stuck open and the engine does not reach operating temp that the computer is looking for. This is a very common concern on this truck. You need to replace the thermostat.
The p0340 is a cam to crank relation ship code, as if they are out of time with each other. This engine has a variable camshaft timing on the exhaust camshaft. There is a solenoid that controls this camshaft timing. If the solenoid is clogged or going bad, it can cause this issue, also somewhat a common issue. I would replace the thermostat and clear the codes. See how the engine runs and if the p0340 comes back, if it doe then you may need a camshaft actuator solenoid. The stuck or clogged solenoid will cause a erratic idle and lack of power.
Customer: replied 7 years ago.
so replace the thermostat first. and see if the codes come back again? then if the code P0340 comes back its most likely the cam actuator solenoid? is there any possibility it could be the just the cam position sensor? and if so, is there a way to test it?
Expert:  MPMoore replied 7 years ago.
It may be a camshaft position sensor, but this is not very common. No way to test it, just check the power and ground to the sensor.
Customer: replied 7 years ago.
you sound like your pretty sure that its the camshaft actuator solenoid. and from what ive read elsewhere, it looks like its a fairly common thing to fail on these cars. so i will go ahead and replace the thermostat and see if the p0340 come back, and if so. ill go ahead and replace the cam actuator solenoid
Expert:  MPMoore replied 7 years ago.
Let me know what happens.