Strong engine stumble April 25, 2020, 10:30:11 PM Driving normally at highway speeds, this past week I have picked up a strong stumble. So much so, it feels like the fuel pump or ignition is shut off. Being as I picked up a cheap fuel pump from Craigslist, I assumed that was the cause. Hooked up the gauge and I have a perfect steady 42 psi with vac line off and about 34 with it on. Preassure rises with throttle, so everything seems to check out. I run codes, I get a 91 (lean drivers side) 34 (get out of range) and a air injection code. I pulled the egr off since its really easy to get to, and its stuck and has a ton of black gunk. Cleaned it up, and minimal preassure moves it in and out. Looked at the smog pump, and I have a missing hose clamp. Whoops, wonder how long its been like that. Hooked that back up. Unfortunately, engine was too hot to do the o2 sensor, so I let it be for now. After messing with the egr and smog pump, I ran codes again. They still show up, havent cleared them yet. I then ran an engine cylinder ballance test. The motor isnt running smooth, but I had just ran codes and figured why not. Got a 90 the first time and a number 5 the second. Now obviously the o2 is going to affect the car running well and that is in the works for tomorrow. Ive noticed a drop in gas mileage too, so if thats all it is it would make me pretty happy. So the plan right now is to swap that o2 and see where I am at tomorrow. Ill probably pull the number 5 plug while I am there and make sure it looks okay, but the plugs aren't that old. The real question here, I've lucked out pretty good on o2 sensors. The only time ive really had to replace them was for emissions. I never really noticed a big difference in how the car ran. Can a bad o2 cause my bad stumble?