173 code and stumble at light loads

A few weeks ago I had 2 valve springs break (#1 intake and #4 Intake about a week after the #1). After the number 4 broke I changed all the valve springs with new. I noticed the car stumbling a bit at about 2500 RPM under light cruse. I thought it was a tune I did but revertng to different tunes did not change anything. I was able to get a CEL and I pulled a 171 (hego switch rich) So I put in 2 new O2 sensors. No change in the stumbling. it idles fine and runs strong when I push it.

The Wide band reads around 14.1 to 13.7 during the stumble. Today I noticed the wideband went to 10:1AFR while holding the car at the point where it stumbles for about 60 sec. Then I pulled the 173 code (hego rich).

I pulled the 4 injectors on the passenger side (W/B and spring history are all on passenger side) and they all ohmed at 16.1. I put 12v to them and they seem fine. I did notice # 1 and 3 are much harder to blow threw when voltage is appled than # 2 and 4?? Strange??? I did not pull the other inj's B/C I need to pull the upper intake to do so and all the probs seem to be on the pass side.

I was thinking either injectors or possible valve guides?? perhaps the valves are sticking and that caused the spring issues and now with new springs they are hanging up and causing the rich???

Any suggestions or thoughts?? A Running compression test was my next thought but not sure??

Interesting... What made you think it was a ground issue??

Well I started thinking vacume leak.. So I removed my upper plenum, AGAIN!! and found the lower intake bolts very very loose. I retorqued them to 25fps, and test drove it.

At first the stubmling ws still there and it appeared to be rich (around 13.9) But after 10 minuts of driving it seemed better and by the time I was on my way back it is about 90% better. No codes.

I wonder if adaptive learned the air comming in and richend up the mixture to compensate?? Or is it a cold hot issue. B/C once it was good and hot it seemed 90% better.

I will let it cool and retest tomorrow.