It is unusual to get coolant into the exhaust via an intake manifold leak, not unheard of just not usual.
Usual with 4.0l is a cracked head from past over heating or a bad head gasket.
Most common reason for 171 and 174 at the same time is a dirty MAF(mass air flow) sensor.
MAF sensor tells computer the amount of air coming into the engine and the computer bases the fuel needed on that data.
After the fuel is burned the O2 sensors tell the computer if mix is lean or rich.
If the air flow data and the O2 data don't add up to the computers calculations of the amount of fuel that should be being used, you get a code.
Since you are getting codes for both banks/sides of the engine the common denominator is the MAF sensor, or computer itself.
If it was a lower intake leak, then only one bank would be effected, if it was a failing O2 sensor it would only have 1 code.
An upper intake vacuum leak can also cause the dual codes, to test for vacuum leak, warm up engine and let it idle, should be about 700-800 RPM, now unplug IAC Valve wires, idle should drop to 500 RPMs or engine may even stall, either is OK, it means there is no vacuum leak.
If idle stays high then there is a vacuum leak.
On the 4.0l the MAF is at the air cleaner and has an air plenum(tube) that goes to the upper intake, if that air plenum has a leak then it would have the same effect as a dirty MAF sensor, not all the air coming in is passing thru the MAF sensor.
The PCV(positive crankcase ventilation) system is part of this, the oil filler cap and dipstick seal the crankcase and valve covers.
The PCV Valve pulls air out and the vent hose(from oil filler tube to air plenum) allows "metered" air to come in.
Often if you unscrew the oil filler cap while engine is running engine may stall or idle will go high, you created a vacuum leak.
Last edited by RonD; 09-25-2014 at 09:12 AM.