I have a 95 Astro that has a very rough idle and surges and cruising speeds, like 45 mph and 65 mph. Only surges in overdrive at those speeds. Will not surge if kept at higher rpm like in drive. Exhaust is very strong smelling, and dark. Sucking gas like it is going out of style, 9 mpg, terrible. So far I have replaced the following: EGR valve, O2 sensor, muffler, fuel injection spider, fuel lines inside intake, spark plugs, wires, rotor, and cap. Previously had catalytic converter honeycomb fall apart and clogged muffler. Muffler shop swears that cat is now completely empty. I have checking out a lot of these threads and found a common ground with the fuel lines, so I opened up the intake plenum and found black, almost oily-like substance covering the entire left side of the intake, but fairly clean on right side. Also found carbon had completely clogged port leading down to egr valve, cleaned out thoroughly and replaced the fuel lines and injectors since I was already in there. Previously had two codes on ECM, EGR valve and O2 sensor. Which is why I replaced both, just to be safe. Throttle position sensor passed test. I am completely at a loss here. I am about to leave it in a parking lot and hope someone steals it.
It fits our family very well, and I hope to keep this van for a while. Can anybody point me in the right direction? Could ECM failure be causing my issue? The ECM failure code has not popped up yet.