Engine looping check engine code 170

Code 170 means the computer can not adjust the fuel mixture by normal methods. Could be the O2 sensor, or a problem with the fuel injectors.

Interpreting the Results
of the Engine Compression Test.The idea behind the Engine Compression Test (in the case of a Misfire Condition or Rough Idle Condition) is to find out if any one engine cylinder is not contributing 100% of its power to the overall engine output. If only one cylinder has lower than normal compression, your GM 4.3L (or 5.0L, 5.7L) equipped vehicle will run rough or cause a Misfire Code to set and turn on the Check Engine Light.
So then, to wrap things up, the individual cylinder compression readings of each engine cylinder can not vary more than 15%... and this is how you can find out:

1. 1Grab a calculator and multiply the highest compression reading that you recorded by .15.
   
   So, let's say that cylinder #4 gave you the highest reading of 170 PSI. Well 170 X .15 gives you 26 (25.5 rounded off).
   
2. 2Now, the next step is to subtract 26 from 170... which gives us 144 PSI.
   
3. 3So then, 144 PSI is the lowest possible compression reading that any one of the rest of the engine cylinders can have. Any compression reading below this.. and that engine cylinder will misfire..
   

What you were told is that if the thermostat is not opening
soon enough or opening too far,it will effect what is called
closed loop. That is when the engine is warm and the O2 Sensors
take over fuel control, verse the computer on start up in open loop.

The Coolant Temp Sensor is the part doing the closed loop thing

So both have to be good

The stat should be changed every 5 years anyway
The temp Sensor can be tested

Also the o2 sensors can be viewed a number of ways

To work at home without knowledge of OBD Systems
you can't do much. Like trying to play doctor without
an 8 year degree to learn the craft

170 is on the cool side of operating temp so that is not a worry. What year model? Check engine light on? Any codes?

Generally when you get a code for both banks, you do not have an engine failure, but you probably have a significant vacuum leak. First check the rubber hoses around the PCV valve to motor intake and if any rubber is squishy or oily that would indicate a leaking hole. Also check around the entire intake with carb cleaner (engine revs while running if you spray the cleaner near a leaking gasket or intak hose hole).

WHEN ENGINE GOES CLOSED LOOP TO OPEN LOOP.YOU HAVE A RICH FUEL MIXTURE.YOU HAVE A VACUUM LEAK.BY YOU HAVING ROUGH IDLING.AND A HIGH MILEAGE ENGINE I WOULD DO A COMPRESSION TEST OR CYLINDER LEAK DOWN. CHECK FOR LEAKING VALVES AND LOW COMPRESSION .THEY BOTH WILL CAUSE ENGINE TO IDLE ROUGH CAUSE MISFIRE.CAUSE OPEN LOOP CONTAMINATE HO2 SENSOR CAUSE A RICH FUEL MIXTURE.

try the "tap test" on the ecm. After closed loop,just lightly tap on the computer,you may see it change or stall.Mine did that and the ecm was bad.

P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control
This means that the engine coolant temperature (ECT) sensor indicates that the engine
has not reached the required temperature level to enter closed-loop operation within a specified amount of time after starting the engine.

A code P0125 may mean that one or more of the following has happened:

• Insufficient warm up time
• Low engine coolant level
• Leaking or stuck open thermostat
• Faulty coolant temperature sensor

The simplest thing to do is to reset the code and see if it comes back.
If the code comes back, the problem is likely going to be the result of the above causes (faulty thermostat, faulty coolant sensor, or a low coolant level).

Insufficient Coolant Temperature For Closed Loop Fuel Control. Bad thermostat most likely.

oxygen sensor