service engine

I have a 99 1500 van and the service engine soon light came on a couple of weeks ago. It still drove pretty good. Seemed to lose a tiny bit of horsepower. Today it started flashing and the engine ran rough. It has little power and the engine is so rough that when I give it gas it shakes. It almost feels as though the tires are bad it shakes so bad. But I know the tires aren't the problem. It feels as though the plugwires are mixed up or something. Could it just need new wires and plugs? It has 160,000 on it. It's basically a work van and I need to drive it daily. Are they hard to replace? Any other suggestions?

The engine running rough enough to cause the shakes isn't too good. The fact that the service light came on says that it is likely a problem with the ignition system (fuel injection systems could also possibly do the same, but it is less likely). If it hasn't been serviced in a while, you might be up for a new distributor cap. The ignition module could be going bad, but I suspect that they typically just die (like mine did) and the engine won't start at all. A bad coil will cause weak spark and could be an issue. I would replace the cap and rotor along with the coil. If the plug wires are questionable then they should be replaced too. I would venture to say that the plugs should be replaced, especially if they are the originals. Get the best quality parts, don't go cheap here (I prefer Napa Auto Parts for ignition and electrical in general), but I wouldn't rule out Delco parts from the dealership either.

...One more thought (naturally *after* I hit the send button). First check the codes on the computer. Many autoparts stores will do this for free. This will tell you what system is reporting problems (maybe the ignition is fine and there is something wrong with the emissions system). This should be the first step.