Unfortunately, I hae been extra tied up and only able to do limited MCF stuff since last Saturday.

I mentioned check your vacuum lines. They are the thin plastic lines that had rubber connecting fittings on the front (and they are just about the only vac lines). Yes, the car runs fine (so did my friend's car that got a funky EGR code), but if they are crapped and NOT holding vacuum, that can have an effect on fueling. You can also try misting starting fluid around the top of the engine while it's idling. If it have a vac leak, the fluid gets sucked in and changes the idle. Now again, in case of my friend's 3800 Grand Prix, this fruited nothing. It was old fashion eye balling and fixing crap that looked bad.

Now I tried to look that code up in the shop book a couple nights ago and it comes back with nothing (makes no sense to me). But looking at one of the pieces of information you found:
Could be the answer. I would look into this. I believe that can be dictated by things like:
- Vac leak
- Failing fuel pressure regulator
- I'm guessing but maybe an injector running a little heavy on fuel
- Possibly an upstream O2 failing to give accurate data to the PCM to aid in fueling control

I would explore this as a cause as well as ensuring the EGR wiring is not damaged and working propely.

You've proven your EGR is good, so the guy at Autozone is just a guy at Autozone spouting off what their system says to do.

 

This web site may be of some help. It lists the causes and diagnostics for the P0402 code:

OBD II Code P0402

 

As of now, no I have not replaced the o2 sensors yet. The reason is if one was bad I would get a code for the o2, the only code I get is P0402, that's it.. It's such a vauige code and covers so much... The EGR is working perfect.. I disconnected the egr and the car won't even run.. , that's a good sign, shows the egr is working correctly.. I have all the tubes, and egr replaced and cleaned.. That's why I'm a t a loss for a fix... Thanks.. Mjc....

 

I did the EGR test yesterday.. I was told to remove the EGR and start the car without the egr in place, they said if the car DOES run good, there is an issue with the egr valve. If it was running horrible, or won't start, EGR is good.. I did what it said and the car ran horrible if starting at all...i am replacing the fuel sending unit today.. I have a problem with my gas gauge not being correct. I'm just shooting in the dark to see if it will help..
I also have the GM manuals on the Monte, the huge shop manuals... And havent found the P0402 OBD2 code at all.. No clue why.. Also guys, it's not really a money issue, it's the code is so vague it could be 20 differant things.. But the 02 sensor has to be good otherwise I'd be getting a O2 code.. But I'm not.... Frustrating as all heck !

 

Thanks so much.. Just frustrated as heck because of the stupid code.. I wouldn't mind buying the parts to fix the damn thing, but the code is so vague it' doesn't make sence to just start replacing parts till it runs good.. If I was to take it to a shop right now, first thing they do.. Replace egr valve.. IT'S A GOOD EGR.. It's the third egr to be installed, then reinstalled in another car and didn't code, and is perfectly working.. My wife is using my original EGR

 

This is what I have done to this point..

Cleaned inspected EFR SYSTEM, cleaned and replaced PCV valve. Cleaned and checked out the idle position sensor the MAF sensor cleaned and checked.. Replaced Air Filter, cleaned various parts and sensors.. Checked for vacuum leaks, so far all look good with the starting fluid test and visual inspection..went thru the lines , wires. Tubes gas cap, etc and have seen nothing disconnected or bad.. Just want the light OFF ! Thanks everyone for your assistance, much apprenticed .. Thanks.. Mjclemm..

 

I will have my cousin do that.. I don't have the tool.. Question is , will this code "clear itself"? Or does it have to be cleared with a programmer / code reader?

Basically what I mean is, is it easier to see if it will code again? Or see if it doesn't come back on? I cleaned so many things I may have fixed it. I talked to many mechanics and they all said Map, Egr, o2sensors, etc.. Can't be bad or they would code as well. I believe this is one reason this is so hard to diagnose. It has such vague info on how to track fix it. "Could be".........?????

 

Typically something like this requires a good amount of "cycles" or correct commands before it clears itself. I'm not sure how many.

 

Lol.. Thisis my delema.. I have no clue weather or not the problem has been fixed... How do I actully tell if it is fixed or not by just driving around... Let's say for example , it ISN'T fixed... I drive for 125 miles, still have the CEL on.. I was told "you may need another 100 miles". Ok, then I go another 125 miles, still have the CEL.. WHEN OD I JUST SAY WTF ? Lol...
Other example i. Do I clear the codes, drive around for History, when the history is good enough (by the beeper that the EMMISSIONS place let me use to make sure the PCM has history on enough monitors) and by then if the CEL doesn't come back on, it's fixed, if it does code again, I still need to chase down the problem... Either way it sucks.. Even all the Garages around here are saying it could be anything.. Well. I'm not gonna pay for a car to get driven around and replace all the GOOD parts to find its still an issue.. Why can't they do a sniff test to see if in fact it WILL pass emmisions even though I have a "CODE" no one knows exactly what it is....aaaaggggrrrrrrhhhh,!!!! And to top it off the car RUNS GREAT ! No issues at all.....
Please I have exhausted almost all avenues of diagnostics...
(wife just said she's gonna beat it with a Sledge hammer...lol...)


OHHHH almost forgot.. Today I replaced the gas tank sending unit and float assembly..I had bought it from another member from Monte Ss Forums.., well it went EXTREAMLY well replacing it.. Had alitle rust to deal with, no biggie.. So, swapped it out, tested to make sure NO LEAKS , put back together and off for a test drive and more cycles thru the computer.. We stopped, dropped off a DVD we rented, fill up my tank for $51.50 dollars and we proceeded with a joy ride.. For 5-6 miles down the road when I heard a "Pop" and the car died almost IMMEDIATLY."... To my supprise, this hasn't ever happened to me, well the strong smell of gas soon filled the air, even before stopping the car.. Looked at the gas gauge, it's down about 1/8 -1/4 less than full.. (I just filled up, litterly, 5-6 miles ago) how can this be, maybe a bad sending unit I bought ? Well after the car stopped , got out and looked to the rear of the car.. GAS EVERYWHERE ! This sucks, me, my wife and daughter and our 2 dogs are now stranded on the side of the highway.. Can't get any help from the police because of the major shootings here in Milwaukee (Oak Creek), about 1- 1 1/2 miles from my house.. We watched 3-4 police cars drive by me on the side of the highway and did t. Even bother to see if we were alright n stuff.. Ticked me off.. So my son had to come and get my wife and daughter, + 2 puppies.. Somimfinally gor a tow truck to tow it to my house.. So my son had came back..... Went home to check out the OLD sending unit.. All looks good but something seemed to be off a bit... 2 of the 3 clips that hold the cables n wires were still on the old one.. I had forgot to install them on the newer pump.. That's why the lines blew off while I was driving.. A stupid but simple mistake.. Only cost about $10 in fuel and $90 for the tow.. Got great mileage while it was on the back of a tow truck though..lol". Thanks again so much for the ideas and suggestions.. Mjclemm"

 

I know in my state, they scan the onboard computer of '96 and newer cars. Older cars get basically put on a dyno to do a tail pipe test. If you come in and your car is not in a "ready state" on a '96 or newer, they will test it the old way on the rollers. NOW, if you come in, FAIL to test by scanning the computer then the ONLY way to pass is by the computer.

But this is the system in my location (and it's not even state wide).

I know "some people" who have maye, maybe not, cleared the computer and readiness data, went to get checked, was told it's not ready, had it put on the rollers and passed.

Unfortunately, I am really drawing a blank on the EGR issue. The odd part is, I believe this began AFTER you did the non-fouler trick for the downstream O2. This may sound silly, but when looking for a cause of the problem, can you check that the non-foulers on the O2 are tight?? THat there is not a hole or leak from them? Not sure if it will mean anything, but it's just a curiousity.
Otherwise, I am stumped. I'm also further stumped that this is not a code in the shop book!!