Weird engine condition.

My 96 Roady wagon has developed an unusual problem. It runs like a top, and has for the 4-5 years I've had it, and it is happy to run on regular gas. Anyway, in the last few weeks, when driving, under normal road conditions, all of the sudden the motor makes a rattling sound like pre ignition from bad gas, or gas with too low of octane. It'll do this for maybe 4-5 seconds, rattle a little, and then the service engine soon light comes on. After the episode, it resumes running perfectly with no rattling. The light will stay on for a short period of time, then go off. Has anyone head of or experienced a similar problem? Thanks. And, no Sprocket, I won't give you my car!!

Did you get BAD GAS?
Dump the fuel and get fresh stuff if its just this tank.

Go with atlantadan, and check the codes before you do anything. I would suspect an O2 sensor. It might be a bad knock sensor as well. You will know what the computer is trying to tell you with the SES light.

I don't have an obd 2 tester, but I guess I'll need to get one. Let's just say it points to a knock sensor, as Fred has suggested. What exactly is a knock sensor? If it does what the name implies, I'm sure guessing that is the problem. Now that it has been doing this more frequently, out of the blue it starts the pre ignition thing, rattles a little, then goes away. What does that part cost, and once I determine for sure that's what it is, where is it located? Is it a simple thing to replace?

EGR sticking would be my first guess.

The knock sensor is located on the block below the exhaust manifold. I may be on the left or right. The knock sensor senses vibrations caused by detonation. There may also be false knocks, but they are usually programmed out of the computer. When the knock sensor senses a knock, it retards the timing until the knock goes away.

You could also have spark plug wires arcing to each other, or to ground. On an LT1, the spark plug wires must be routed as they came from the factory to keep them from arcing. Put the metal shields back on them as well.

They are not expensive, and are screwed into the block. Depending on access, they can be easy or difficult.

you can pull the codes from the AC display. many youtube and google videos on how too.
will work in the Caddy too.