95 ASTRO Rough IDLE!!! HELP

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.:rofl: 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.

I would start with some small simple things. Have you done a fuel system leakdown test? Have you checked fuel pressure? Have you replaced the fuel filter? You said you replaced the spark plugs, cap, rotor, etc... Did you use aftermarket or AC parts? I found my van ran like a piece of (we won't say) with aftermarket parts, switched to AC Delco parts and runs great. Have you checked the MAF - that will sometimes make the vehicle run rich and cause issues with the O2 sensors and cat converter.

Start with the basics. The answer is often simple and is missed because we look at the more difficult things first.

I did replace the fuel filter not too long ago. I replaced with Delco plugs, but not Delco cap, rotor, and wires. This problem happened while Delco parts were on there though, so I don't know if that would help much, but I'll try anything. With respect to the MAP sensor, is it possible that this could be the problem when I don't have a check engine light indicating a problem with that sensor?

I was referring to the Mass Air Flow, it is located just behind the air filter. I know many people swear by the code readers to answer all of the mechanical problems. I have been repairing boats for over 22 years and many times the computers don't tell us everything. I would perform the proper tests as per the manual to check the sensors since you are not getting codes. The MAF - Mass Air Flow is easy to get to, the plug is accessible just by openning the hood.

Also make sure to do a fuel leakdown test and a fuel pressure test. These will not give out a code. You mention dark exhaust and strong smelling indicating that not all of the fuel is being burned properly and the van is running rich. The fuel tests are very important in this situation. Another thing is to make sure your air intake is clear - check air filter (which I am sure you already did) and make sure there is nothing in the air intake. My father many years ago had a S-10 and some sort of animal decided to build a nest right in his air intake and gave him problems that even the dealer could not find. He ended up finding the problem when he changed his air filter and happened to look down the intake pipe and found that nest. His truck ran like it should after he removed it.

My astro is a 95 and is doesn't have a MAF sensor. According to my repair manual the MAF sensor was started on the 96 models. I will check the fuel pressures like you said. What about the camshaft and the crankshaft position sensors? It almost seems like the timing is way off on this. I can't seem to manually advance the timing and see any difference in idle at all, which leads me to believe that it is completely done by the computer, which brings me back to wondering if I need to replace the ECM.

Call me silly but if that cat is not working right your car will run like crap because the computer is trying to make up for what its sensing in the exhaust. ALSO if your throttle positioning sensor is shot, it will run bad for the computer has NO idea where the trottle is at and is just guesing as to how much fuel to air it needs.

I would also start the van, have someone rev the motor and see just how much exhaust is coming out the tail pipe, for if its being gunned, and hardly anything is coming out, that cat is still clogged, but in any case, with a computer controlled motor, you need the cat to be working as it should or its going to reak havok on you.