W124 E420 Stumbling under load

[srdavis872]

I've been trying to figure this issue out. It seems it's worse when it gets warm. If you drive the car like a grandpa, it's fine, but if you try and accelerate with any sort of urgency, it'll sit there and stumble/misfire until it get above approx. 2k rpms then it'll take off fine. I changed fuel pumps and fuel filter. My next step was going to be spark plugs. I inspected them today and they do look like they've been in there a while, but I cleaned them up and put them back in, and no improvement at all. I'm sure it could use new plugs, wires, dist. cap, rotor, etc, but money for this car is tight and I'd like to make sure that's it before spending several hundred dollars on all that.

The only other issue it has when running is if you stab the throttle when in park, RPMS will raise fine, then drop very low and almost stall, then return to normal idle. I'm not sure if these could be related.

I've always worked on my own cars, but this is the oldest car I've owned and it is making me realize how dependent I've been on just plugging in a computer and seeing everything that's happening.