400 ppm nox at idle 202 is the limit now what

Hi!

First of all, HC (Hydrocarbon) are the residue of petroleum based product combustion. If your HC reading are higher than the OBD2 legal limit (220 ppm), the most common causes could be a leaking fuel injector, abnormal oil consumption, a faulty Oxygen sensor or worn out spark plug / distributor cap / spark plug wire. To be honest, I would need more accurate details such as NOx ppm, CO ppm, CO2 ppm and Oxygen ppm and if there is any repair that have been made on the car recently to give a proper diagnostic.

Warm regards

Usually changing the spark plugs, air filter and an oil change will fix your problems. If your oil is old, you can get the high carbon. I don't usually change the spark plug wires and I just take the distributor cap off and clean the contacts.

your distributor make be a hair off if the bolt came loose, or your throttle cable may be a little loose

Hello! when you say you checked the MAP sensor what do you mean? Did you take voltage readings at idle ? A vacuum leak is the likely culprit, especially to the MAP...The minor shake at idle being the major clue...Send a comment...guru..saailer

I’m happy to help further over the phone at https://www.6ya.com/expert/david_6df67de3b14de867

A throttle positioning sensor or idle sensor can cause these problems, low fuel pressure can cause these problems also low fuel pressure can be caused by a faulty fuel pressure regulator.

Since your cat was replaced you should be looking at fuel problems...even gas cap seal....check fuel pressure,fuel regulator,and evap system.>canister or purge solinoid,o2 senser...high nox is caused by the cat or fuel problems on these engines...high pressure in the combustion chamber...lean condition>air leak on hoses,or high compression caused by carbon build up ...there is no EGR on this car so don't waste time looking for it...hope this points you to your problem

have your EGR system checked . sounds to me like its not working or clogged

Don't do it.  You are smart enough to know that this tune up is full of fluff.  Find another mechanic,  this is either a dealer or a thief, maybe both.
Do you know what MPG the car got when new (are you original owner)?  If you do, and If it's getting the same mileage it did when new,  you don't need much of a tune up.
you probably need : 1.air filter
2.oil change and filter
3. plugs  if > 100K since last changed
4. MAYBE, just MAYBE a fuel filter, but if you don't have a performance problem,  probably don't need it.
5. If you don't have a significantly different mileage from new, and the car idles and runs rock steady, you don't need wires now ... tomorrow might be a different story ... but you'll have symptoms first.

Lets look at what is BS in the list:
I call BS -> "ADJUST" in "Renew & Adjust Spark Plugs", it sounds great but in several dozen plugs I have checked, they were all 100% to spec out of the box,  they are not made by monkeys.
I call MAYBE BS "Inspect Or Replace Distributor Cap, Rotor"  I think your 92 is electronic ignition, 93 was because I had a 93 honda.  So I call Probably.   Now I call definite BS on "Inspect or Replace",  since they aren't replacing many of them, but at that price you paying for a new one.  If they don't use a microscope with heavy backlighting to inspect the cap and roter THAT YOU DON'T EVEN HAVE,  they are wasting their time and your money by inspecting it.
I call BS "Service Or Renew Air, Fuel Filter And PCV Valve", if they can't say Replace Air, Fuel filter and Inspect PCV,  I sure wouldn't pay them $390 ... are they on crack;~)!  They are NOT going to "Service" the air and fuel filter, if they understand english, they should say what they mean,  if they can't do this, do you want them servicing your car?
I call BS "Adjust Ignition Timing And Check Advance" What on earth do they think could possibly have changed the ignition timing, and how in the world do they think they are going to adjust it, by rotating the distributor cap you don't have?  ... it's got an electronic ignition (98% sure it does).


I call BS " Make Necessary Fuel Adjustments", what fuel adjustments, Have them explain a SINGLE fuel adjustment in your car they are possibly qualified to make unless they have a $100K clean room. The car is fuel injected,are they going to disassemble the injection pump in their clan room and mic and replace the fuel rotor (read:NO). 

I call BS  "Service Battery", ok, MAYBE they will rinse off the top and add distilled water or at least check it - takes you 5 minutes if you are unqualified.
Keep in mind no one is right 100% of the time, but if your engine is Injected and Electronic ignition (easily verified), most of this is useless from a generic list of cars from prior to the 80's or 90's, and I'm not wrong that often.
I call MAJOR BS " Does Not Include: Adjust Belts",  OK, never mind this is a trival thing to do if  it's needed (rarely),  but they are charging you $400 for what they will spend an hour at most to do.

I call MAJOR BS ->No Oil change listed in the service ... THIS ALWAYS NEEDS TO BE DONE ... EVERY SCHEDULED SERVICE

O2 sensor helped me but not enough to pass. Loosen your distributor bolts, one on each side, turn your distributor counter clock wise about 1/4 inch and tighten bolts. This will raise your CO but should reduce the NOX. When the vehicle is passed, undo the changes.

Do an oil change with 20W50 oil (or one grade higher) to prevent blow by during the test.

You current oil has HC from blow by though the rings.

Do a fresh oil change will lower the HC.

========
Change spark plugs,wires,cap and rotor if they are over 24,000 miles
========

Make the smog check appointment for the EARLY MORNING. Colder air will help the fuel burn better.

========

Clean or change the air filter and pcv valve.

Clean Mass Air Flow sensor with CRC Mass Air flow cleaner or electronic part cleaner.

========

Do a quick wipe down on the wires and cap to take the moisture off.

========

Check spark plug wire contacts for corrosion.

========

Fill the tank to around 3/4.......just in case your fuel pump is weak.

========

Ran the truck for 20+ minutes on highway before the test.

========

Do not carry excessive cargo on the truck bed.


These are the little things I would do to get the HC and CO down.


Please post more information on the comment window.