Warm idle fluctuation with slight backfire [VIDEO]

[turboguard]

So I just rebuilt my quadrajet using cliff's HP kit, and while it definitely improved my throttle response/performance (no more bogging from a takeoff) and gas mileage (this is the first time I've seen 200 miles between fill ups!!!), I've developed an idle fluctuation when warmed up:

https://www.youtube.com/watch?v=nQJdGQ06ES4&feature=youtu.be

There is a low thumping sound from the exhaust when the idle drops which I can only assume is a slight backfire?

Also, if I try a warm start after letting the car sit for a while, it will sometimes stumble and die if I don't give it a little gas first.  Hasn't died in traffic yet, but it almost acts like it wants to.  Picks right up with no stumble or bogging when I floor it from a stop.

I also installed a brand new TPS and MCS as well.  The only other thing I changed were my spark plugs since they had fouled up pretty bad due to the carb running fairly rich before and also some oil leakage (replaced with NGK V-Power plugs)

What would be the most likely cause of this idle fluctuation? My carb didn't have it before I rebuilt it.

The other thing that is odd about my quadrajet is my airhorn doesn't have a rich stop screw (as in there isn't even a hole there where it should go). My carb number is 17085204, which according to my resources SHOULD have the rich stop screw, so I'm thinking the carb is kind of a mish-mash from the PO.

I still tried to set things the way they should be, but I don't have a dwell meter to exactly dial in my air bleed valve.  It seems to idle the best at under 2 turns out from seated, which seems low?  I have the idle screws turned out 5 turns each, but past 4-5 there doesn't seem to be any change in rpm/vacuum (vacuum is about 21 hg).  If I fully seat both screws the engine stumbles and dies.  Choke is fully open, and if I cover the primaries the engine does start to die as it should.

Another thing I just noticed was my Idle Stop Solenoid seems to be engaged all the time when the engine is on (I actually have it turned down so it doesn't interfere with normal driving)...don't know if that is a separate issue or related.

So basically, running like a champ except for this idle (which is embarrassing when stopped in traffic ).  Any advice as to what I should start checking first?  Maybe something to do with the fact it was running extremely rich before is why this problem just started?

Car info:
1985 Trans Am LG4
Stock except for AIR and Cat delete
Edelbrock 14"/3" open air element
MSD cap and rotor, Accell super coil and, plug wires

[turboguard]

Decided to make another video tonight...there is definitely a loud hissing coming directly from the carb, don't know if this is normal or not.  Theres also a loud whistling when I open the throttle plates which I assume is caused by maybe an imperfect fit, don't know if it has any major effects or not.

Please let me know if anything in particular jumps out as a major issue to anyone, thanks!!

https://youtu.be/D-TqLcbpNHw

[Cliff Ruggles]

Did you adjust the new TPS via the factory Service Manual?

Did you adjust the upper idle airbleed screw in the airhorn per the Service Manual?

Is the float set to factory specifications?

Might want to set the idle speed screw right against the linkage so see if it stabilizes idle speed instead of letting the computer control it.......Cliff

[turboguard]

I set the float as precisely as I could to 11/32 per the instructions

I haven't messed with the TPS adjustment (mainly due to not having the right tool to turn the little hex head), but when I tried to check the voltage by backprobing I was getting weird readings from my multimeter (the voltage would fluctuate slowly up and then down and sometimes show negative??), on both my old TPS and my new one...not sure if I was doing it wrong or my multimeter won't work right.  I actually found a multimeter that apparently reads Dwell that I'm going to pick up today:

http://www.oreillyauto.com/site/c/detail/BOST/FIX7677/N1001.oap?ck=Search_multimeters+%26+analyzers_-1_1430&keyword=multimeters+%26+analyzers

Would this be sufficient to set pretty much everything to what it needs to be? 

[Jeffs68]

Sounds pretty normal to me for an 85 T/A. The only thing I would do is get rid of those "novelty" NGK plugs and put a set of  A/C Delcos in.

Double check your timing as well.

[turboguard]

Sounds pretty normal to me for an 85 T/A. The only thing I would do is get rid of those "novelty" NGK plugs and put a set of  A/C Delcos in.

Double check your timing as well.

The V-Powers aren't really a "novelty" compared to other plugs out there, literally just a regular copper core plug with the V-tip which supposedly helps burn (couldn't hurt either way).  Plug gap is at 0.35

My timing was 8 degrees advanced with the ECM disconnected.

[turboguard]

So I'm starting to think my idle problem has to do with the fact my airhorn has no rich stop screw.  I've adjusted everything the best I can and it runs pretty good while in drive, but in park or neutral the idle is still very rough.

Would you be able to sell me the appropriate airhorn for my quadrajet?  Or would it be possible for me to drill in a place for the rich stop screw myself?

[Cliff Ruggles]

Can you provide a picture of what you are talking about (rich stop screw) and where it is missing on your carburetor?

[turboguard]

Can you provide a picture of what you are talking about (rich stop screw) and where it is missing on your carburetor?

Sure, I'll pop the airhorn off when I get home this evening and post up some pics of everything.

[turboguard]

Pics of the airhorn:




Close-up of where the rich stop screw should be if this were the correct airhorn:


The carb number:

[turboguard]

Another pic of the carb w/o airhorn:

[Cliff Ruggles]

I'm not seeing the pics?

[turboguard]

I'm not seeing the pics?

Sorry, Google Chrome tricked me into thinking the links would actually work for other people

Here is a direct link to my album, should work for anyone:
https://goo.gl/photos/jDKXybfKPorA85Hx6

[Cliff Ruggles]

That worked.

That airhorn doesn't have the adjustment most have to adjust or limit the height of the primary metering rods.  It would have nothing to do with idle quality in any way.

I also see that the upper idle airbleed adjustment parts are missing, the one with the two "O" rings on it.  That needs to be in place to fine tune the idle system once the carb is placed back in service.....Cliff

[turboguard]

That worked.

That airhorn doesn't have the adjustment most have to adjust or limit the height of the primary metering rods.  It would have nothing to do with idle quality in any way.

I also see that the upper idle airbleed adjustment parts are missing, the one with the two "O" rings on it.  That needs to be in place to fine tune the idle system once the carb is placed back in service.....Cliff

It has the IAB valve, just had it out for the pics.

I know you say the rich stop screw doesn't affect the idle, but with it not being there, wouldn't that also effect the IAB valve's travel since it would cause the little piston to move further up, pushing the IAB valve more than it should?