AC BLOWS 43 DEGREES AT IDLE HOWEVER WHEN AT FREEWAY SPEED AC BLOWS 55 DEGREES

Do this procedure first before replacing the expensive IAC valve.

Here are the most common causes of idle surge, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake

After the MIL is turned off or the battery was disconnected for some time, all monitors are set to incomplete. However with several short trips with engine getting at least to hot enough for thermostat to open, (I believe 8 is the magic number of trips) most monitors are set, you may be able to pass the test with only one incomplete only.

Turning on the AC forces the idle to rise, if it is working as designed. It may be masking the problem. How does it idle after warmed up and AC off, all accessories off?
Check idle speed, idle mixture needle (if accessible-some are plugged off with anti-tamper metal seals) and do check timing if you have a rough idle. Timing could be spot on, it must be close if it runs perfect, just make sure it is within plus or minus 2 degrees of specifications at specified idle speed, and vacuum advance hose disconnected and plugged off.

Well, good luck with the old dinosaur, lol, as an owner of a '79 Datsun pickup, and now an '87 sedan (Nissan, of course!). We will run them into the sunset together!

Average gauge readings for R134 with air temp at 80 degrees and engine idle are 35-45 psi and 200-250 psi.

The A/C low side should read between 30 and 35 psi. Refrigerant pressure is indicative of its temperature, and 55 psi on the low side is too high and would only provide 60 degree air at the vents.

The following drive cycle can be used as a guide to assist with re-setting monitors when a vehicle specific drive cycle cannot be located. This OBDII drive cycle begins with a cold start (coolant temperature below 122 degrees F and the coolant and air temperature sensors within 11 degrees of one another). This condition can be achieved by allowing the vehicle to "sit" overnight, and then by beginning the drive cycle the next day. Most drive cycles will be difficult to follow exactly under normal driving conditions, so the driver should exercise caution, road safety, and courtesy to others.

1. . Start the engine. Idle the engine in drive for two and a half minutes with the A/C and rear defroster on.
2. Turn the A/C and rear defrost off, and accelerate to 55 mph at half throttle.
3. Hold at a steady speed of 55 mph for three minutes.
4. Decelerate (coast down) to 20 mph without braking or depressing the clutch.
5. Accelerate back to 55 to 60 mph at ¾ throttle.
6. Hold at a steady speed of 55 to 60 mph for five minutes.
7. Decelerate (coast down) to a stop without braking.

you dont,the aircon needs power to run so the computer is telling the engine to tick over at a no vibration speed,if it ticked over at the lower (400)revs,the whole car would shake.....

Code 12 = Recently disconnected battery

Code 14 = Coolant sensor high resistance or shorted

Code 43 = Knock sensor or Electronic spark control circuit fault

Code 55 End read code.

Hope helps (remember rated this).

two things--first replace your cabin air filter.second reverse flush your heater core with a garden hose and that should remove the build up of material in your heater core and restore the flow,hope this helps

WHEN A CAR SHUT DOWN ON HIGHWAY OR FREEWAY.YOU CAN STILL HAVE FAULTY FUEL PUMP.IT COULD BE RUNNING BUT THE FUEL PRESSURE CAN BE TOO WEAK.THE 2.5 ENGINE FUEL PRESSURE IS 6.0 TO 7.0 PSI AND THE 3.3 ENGINE FUEL PRESSURE IS 37 TO 43 PSI. ANOTHER THING CHECK TO MAKE YOUR COOLANT IS NOT LOW.LOW COOLANT CAUSES ENGINE GET TOO HOT SHUT OFF.CHECK PVC VALVE AND EGR VALVE MAKE SURE THEY ARE NOT STUCK OPEN OR DISCONNECTED.AND MAKE SURE IDLE SPEED IS NOT TOO LOW YOU IDLE SPEED IS ON THE FACTORY STICKER UNDER THE HOOD.