Either that or your most excellent valve lapping job must have increased the volumetric efficiency of the engine to the point that it won't idle down!!

Saw CMP Retard was exactly zero in your video. Seems a bit odd. Does it ever change even a little?

 

Thanks Les, CMP retard does change a little, the max reading I have seen is -7.x. I will check all the things you have mentioned here, I don't have a multimeter to check IAC circuit but I think we can rule the IAC out of the equation here as it seems to be working fine. I've been thinking here and, I have had this code for about a year now. In this year I have checked for vacuum leaks over and over again thinking it just be the reason why P0507 keeps setting, then I took the engine out and rebuilt it, put it back in and P0507 still shows up. I'm just thinking if it indeed is a vacuum leak, it would need to be something that was wrong when I pulled the engine, and I put it in wrong again when it was going back together. Because think, I quite literally just went over all the vacuum lines and made sure they were all looking good when I put it back together. Every line I could put a new gasket on had a new gasket. To add to this, when I put the engine back in it and finally fired it up I realized there was a vacuum leak from the T behind the ABS module, I was able to pick this leak out within seconds because of the hissing noise and track it down to exactly where it was coming from. There is definitely no hissing noise here which is strange because again you'd think a vacuum leak this big would be easy to find, this makes me think something is up with the throttle stop screw...

 

Dont forget to check gas tank EVAP emissions system, pcv valve, and pintle in IAC not seating correctly. These are possible sources for an internal leak.
Sounds strange that went from P0506 to a P0507 with the new IAC motor, unless you already turned the screw at some time in the past or something is not right with the new IAC. If you do turn the throttle stop screw to lower air flow enough to get some counts at idle, keep track of exactly how much so it can be put back if necessary. Even better yet, scratch an alignment mark or lightly centerpunch alignment marks in it.

-7 is not optimal cam sensor retard but its not going to cause any real issues. Better than most.

The plot thickens!!

 

Thanks Les, it is indeed weird the P0506 turned to P0507. I've been so busy lately - not much time to check this out, however today I will get back on the diagnosis. Here is my plan of action, first unplugging the evap solenoid, this should keep the valve closed right? To add to that I got a new purge valve when I did the rebuild so the valve should be sound. I'll also take out the pcv valve and see how that looks, I never took it out when I did the rebuild, although I'm not sure, for such a cheap part it might be worth it to go ahead and replace it so I know everything is sound before messing with the throttle stop screw. I think if I get nowhere with that I will have the truck running until IAC counts are at 0 and shut it off then take off the throttle body so I can get a good look at the IAC seating. If I still get nowhere I will go ahead and turn the stop screw, this should be the end of P0507 at last, I will just turn the stop screw until I get 80-90 counts at idle but keep an alignment mark with where it is now just in case I have to go back.

On the note of the cam retard, I'm not sure how it was reading 0 ever, it seems like the accurate measurement was -7.2. I rotated my distributer as much as I could CCW and only brought it to around -6.3. With my distributor having the same problem yours did Les (broken/cracked screw hole) I'm on the market for an aluminum one and with that, I will get an adjustable clamp so I can set the cam retard to 0. Is it most likely drive gear wear causing this cam retard?

 

I would physically take the evap solenoid off the manifold and plug the hole securely with something (probably easier than getting the plastic hose off) and see if the counts change (don't let something get sucked in). IAC and PCV both have such a mounting seal - but of course you can't watch the counts when you take the IAC out - and the PCV does have some intake air leak all the time, so I suppose I would expect it to change the counts if plugged off completely. The mounting seals for those, as well as the upper to lower main manifold seal, the throttle body to upper intake seal, and the fuel injection connector seal can be checked by spraying FLAMMABLE carb cleaner on them and watching the short term fuel trims for both sensors in plots using Torque Pro. I see you completely understand about shooting for 80-90 counts at idle after verifying everything else and being able to go back. You will definitely do no harm. You also may want to check the TPS at closed throttle and make sure the PCM knows it is supposed to be idling. I'll try to get you a TPS value from mine.

If you get an aluminum one, they will almost certainly be Chinese. You might want to consider swapping the OEM cam sensor and quality cap/rotor from you old distributor (and keep the Chinese ones for spares) Make sure to spin the distributor shaft and be certain the cam sensor doesn't rub or hit as the windows pass through it. Mine required a little adjustment when I swapped mine in.

Slop/wear in the timing chain and distributor gear are the reason for cam sensor retard to go negative (assuming position of cam sensor in distributor, distributor gear, timing gears, and cam was made perfectly so that engine was originally at exactly zero)

As far as a distributor hold-down. Know that the bolt hole is larger on an older small block Chevy, but otherwise a hold down from it will work in place of the locking hold down on the V6 (which you will need to cut off the distributor). You can use a washer under the smaller head of the hold down bolt, but probably have to get a longer hold down bolt (and it is Metric).

Good luck! Keep us posted!

 

This is on Canadian Amazon. Not sure what the exchange rate is but it appears to be $79 Canadian with free shipping. They are $40-something in the USA. I'm convinced they are almost all the same Chinese distributor. Mine's been fine for 50K miles.

 

On my 2001, using a Torque Pro gauge the Throttle reading flashes back and forth between 0.00% and 0.39% with the throttle closed.

 

Thanks Les, I saw those on Amazon as well just wasn't sure of the quality, I'll get one of those ordered tonight. Well guys, I'm finally putting P0507 behind me, I checked everything out, and everything was looking good. I sprayed the engine bay in carb cleaner and there was no change in idle anywhere or change in fuel trims. With that, 2 turns CCW on the idle stop screw and she purrs like never before! It has around 70 IAC counts at idle now, I know it's not 80-90 but much much better than it was. I noticed a huge difference in the idle at the first half turn I made and that just barely got the IAC counts back on the board, counts were around 10-17 but a much smoother idle right away. Now with it where it is now I couldn't be happier, I turn it on and it idles just right every time. Thanks again for your help on this Les it's much appreciated!

 

Great!! I love it when a plan works out!! Good work!!

 

I wonder if a misadjusted throttle stop screw could be the problem with a lot of otherwise previously seemingly unfixable rough idle vehicles here on the forum. Guess the easy test would be to look at the IAC counts at idle and make sure they are not zero. Hate to get people into turning this screw *****-nilly without thoroughly checking for vacuum leaks and engine misfires, but the IAC counts shouldn't be zero. I may have learned something today!