Engine 95 GT stalls at idle

[Jasper C]

Im having some issues with my 95 GT. It was running, albeit not very well but driveable, and then I noticed the EGR valve was missing one of the two nuts that hold it onto the manifold,. The other nut was loose, so there was a large gap between the valve and the manifold where I presume air would be able to freely enter the intake. I removed the valve and cleaned it, and checked the diaphragm before reinstalling it with new hardware so it makes a complete seal with the manifold. However after this, the car cant hold and idle for the life of it. It will run for 30 seconds or so after a cold start, then the rpms will start to dip and then overcompensate until it eventually cant catch itself in time and stalls unless I give it some gas. I have recently replaced a lot of sensors before this problem even started, so I'm running out of ideas.
What has been recently replaced:
New O2 Sensors
New MAF Sensor
Both temp sensors/sender
ACT sensor cleaned
EGR valve cleaned
New fuel pump
New fuel filter
Air Filter cleaned

I was able to pull codes both with the engine off and with it on (it was able to keep alive during the self test) and got a few EGR related codes as well as codes 314 and 311 (Secondary Air injection system banks 1&2 inop during KOER test) and code 177 (heated o2 Sensors bank 2 - mixture rich). Given that I have already replaced my O2 and MAF sensors, could this be a fuel pressure issue where the fuel pressure is too high and the only reason it wasn't doing this before I fixed my EGR valve was because unmetered air was being freely drawn in? I also just patched the vacuum lines that ran to the EGR valve and the two that ran to the smog pump output tube. Weirdly enough I tried seeing what the engine would do if I stuck the EGR valve open so I just bypassed the EGR regulator so that line gets a constant vacuum, and it is able to idle with the EGR valve open. Isn't that backwards? From what I've read the only way an EGR valve should be able to stall an engine is by being stuck OPEN not stuck closed.

I know that was a long post but if anyone read through it all and has any suggestions I would be very grateful. Im kinda a loss here.

 

[Jasper C]

bump

 

[General karthief]

Have you check for vacuum leaks?
What is the fuel pressure?
Tune up recently?

 

[Jasper C]

Thanks for the response. Yeah I did find a leak in the lines that control the EGR valve and something to do with the smog pump and fixed those. This morning I put a fuel gauge on and it’s holding a little above 35 when trying to idle which I think is good. I have ran fuel system cleaner and done an oil change recently along with all of the replacements i mentioned above. It seems like fuel is ok, so now I think it’s definitely somthing to do with air. I removed the IAC and sprayed some wd 40 in it as I don’t have any carb cleaner right now. It didn’t seem to help much. Maybe the IAC just needs replaced?

 

[General karthief]

Pull the plugs, see if they are all black (rich) or if certain ones are black, you may have a malfunctioning injector.

 

[Jasper C]

Alright I’ll try that tomorrow and let you know if it helped. Thanks!

 

[Jasper C]

So I had checked the plugs about a month ago and they looked ok, when I checked them today all of them were pretty black and fuel soaked. I replaced all of the plugs since I've been meaning to do that for a while, and that combined with sea foaming the throttle body and adjusting the timing seems to have fixed it! Im going to check the plugs again after running it a bit. Hopefully they're not black again and the old ones were just black from the car not running/a lot of unburnt fuel being in the cylinders.
Thanks for the Help!

 

[RockOn]

Hi, any update now that its 6 months later on plugs?

I was having hard start / re-start issues and it didn't like finding idle.
My situation - #4 and #8 plugs very badly fouled, #3 and #7 not great but ok, the rest look like they should.
I thought maybe exhaust valve seals, but once I pulled the plug and its both rear cylinders and level of build up reduces as you move forward, I kinda thought that was too coincidental.

95 GT - so I run the Cyl balance test and before it failed for #4 and now with new plugs and coil it passes.
I plan to run it a few hundred miles and check the plugs again - could still be valve seals I guess.
Its not blowing any smoke and since it passed the Cyl balance test, assuming its not rings but I haven't done compression.
It has been a 4 year project car with mostly idling in the garage and driveway so hoping just rear oil galley drain around the back valves due to the angle of the engine.
----
So current status is engine passes load test, but hunts for idle when cold, better when warm but not perfect, and I am throwing 136 and 172 O2 codes.
I think these are for lean both sides, but there also seems to be some conflicts in what I can find for the codes. Don't know vintage of O2 sensors, so coudl be those, but both at once? I have seen a lot on dirty MAF or an intake/vac leak...

Any feedback would be great.

 

[General karthief]

@RockOn
I would look for a vacuum leak.