Here is a link to what your EGR valve looks like: Duralast/EGR Valve EGR1067 at AutoZone.com - 1 reviews

Use this link to see how to test it using a 9v battery: http://econtent.autozone.com:24999/z...sheet_egr1.pdf

Where??
 

All the pictures I can find, show it near the front of the valve body, to the right of the alternator. There is no EGR valve there, only the thermostat cavity and pipe. I know what the valve is supposed to look like. I need to know where it is located. Some sites say there is no EGR on the later 4.3 engines.

I did a search for an EGR Valve on Autozone's website for a 2003 and one didn't come up so I assume what you're finding is correct, about later 4.3L not having them. I'm assuming that the build date of your truck is after 6/02?That learned me something, so I guess you can scratch that one off the list. I don't know what's going on in the "Pre Cat". The next one I would try is checking for vacuum leak when the engine is doing that rough idle. One other question, have you done any work on the truck that would have required the Crankshaft relearn procedure?

Other repair work
 

I replaced a bad head gasket on the RH side. It involved removing the intake plenum, intake manifold, distributor, then the RH head. Before starting this repair, I put the engine on top dead center on cyl #1 and was very careful to replace the distributor in exact position. It starts and runs smooth above 1200 rpm. I drove it down the road and up to 50mph with no problems. At the destination about 3 miles away, I stopped, cleared the error code, drove it back home and there were no error codes. Only after it set for awhile and cooled off and restarted did it have a rough idle and P0300. Strange???

If the crankshaft position sensor was disturbed in anyway, you need to do the CKP Relearn Procedure.

But I would start with vacuum and secondary ignition. what kind of wires are you using? Check under the cap for evidence of condensation. If the wires are old, when you first start it up (do this at night) spray a fine mist of water over the wires and see if you see any arcing.

Progress
 

Same old 2002 Blazer LS, 4WD, 4.3L
Latest developments: I finally decided to replace the "Y pipe-pre cat-catalytic" assembly to find the rattling noise. Here is a picture of what I found inside the Pre-Cat. No wonder it was rattling!! I still wonder why it quieted down when warm. Needless to say, the rattling stopped. I drove a short distance. Noticed a lot of pickup and it seemed to run fine. No Service Engine Light. However, when I plugged my Actron Code Reader in, there was the dreaded P0300 "pending" code. The last advice given was to check the spark plug wires & distributor at night with some water misted over them. I will do that tonight. I just bought the 14 year old beast so I don't know if the distributor cap & wires are Delco or not.


(The last time I tried to attach a photo on another Thread, it was very small, so someone please tell me how to resize.) Maybe, just click on it and it will increase in size?

We've been discussing P0300 in 2nd gen forum in more than one thread. Please take a look there. General info and strategy applies to you as well. Verify no vacuum leaks, verify ignition system per instructions, verify fuel system per instructions. Don't assume anything. Then start worrying about P0300. You will need scan equipment that will do live data for cam sensor retard and fuel trim, a fuel pressure gauge, and other equipment noted in the fuel pressure testing thread at the top of the 2nd gen forum. Again, don't skip or assume anything is OK.

Since you removed the distributor you will need to hook up a scanner capable of giving real time data (mostly cam retard) readings and see where that is at. I removed mine and reinstalled exactly how it came out and still could not get it to run proper until I was able to read the cam retard. It has to be at "0" +or- 2 or you will never get it to run proper all the time. Mine was out at like -10 or something so I ovalled out the hold down bolt hole so I could make adjustments to the distributor while watching the cam retard and getting it within spec. Now all is well and no more issues:)

"2nd gen forum"
 

Please excuse my ignorance, but specifically what is "2nd gen forum"? I have been searching with "P0300" and found a wealth of information.

The last time I was just "experimenting", I erased the P0300, the engine was warmed up. Setting still in Park, I then held the accelerator down to about 1200 for a couple of minutes and the Check Engine Light did not come on and there were no error codes. Sounds like it first appears with a cold engine and at idle speeds.

The forum dedicated to the 2nd generation of the s10 blazer... 1995 to 2005