Rattling noise and check light...

I was driving around today and for a while now I have been hearing this rattling noise underneath my car whenever I acclerate at about 40+% throttle. It wasn't too bad but today it was warmer out, around 80 or so and the noise got louder. Then all of the sudden when I was on it one time my check engine light came on. The car got real sluggish cuz I think it went into limp home mode but I am not sure. I got in my car about an hour later and the light was off and everything was back to normal. Then later tonight after driving it a bit again the rattling got loud again then the light came back on. Turning the car off and then back on fixes the light. Is there anyway to check to see what code it is throwing??? Any ideas on what it could be??

are you watchin your temp gauge....your car gets real sluggish when it gets hot...but that wouldn't explain the rattling noise..

It has occured all throughout the temp range. I think it may be loose exhaust and the twisiting of the engine when I get on it causes it to rattle against something but I will have a chance to get under it next week.

Code Display (http://www.thirdgen.org/newdesign/faq/thirdgen.shtml)

This will help us determine what the problem is or at least give us a clue.

When I did the code thing it gave me 12, which is the normal code. The problem is that I get the code only when driving, and when I stop and turn the car off and then back on it goes away.

Can't the scantool interrogate the system while the car is driving and before you shut it down? Following that, I have never tried it but I would imagine you could pull over and short out the terminals and see what code you get.

I got the light again while driving so I pulled over and shorted out the port but I still got the 12 code. You have to turn the car off the get the codes. I am pretty sure the sound I hear is my exhaust rattling against something. I just need to get my car up on a lift so I can check it out. I don't understand why this would be causing my car to throw a code though?????

Don't turn the car off to get the codes or you'll clear the active code.

Isn't it supposed to store all the codes?
I was getting a light while I was driving for more than 15 minutes or so. I went home shut it off, did the codes, and got an EGR code even though there was no light on at the time it stored the code from when I was driving. You should always get code 12. 12 should flash three times, then each problem code will flash three times, then when the trouble codes are done, 12 will flash again three times and all the codes will repeat.
I'm suprised your only getting the 12.

Sounds like an "ignition timing" or a "lean condition" rattle, either caused by overheating, or clogged fuel filter, dying fuel pump etc...If you can pull up the codes by using the Assebly Line Diagnostic Link (ALDL) it will be really helpful...You used to be able to get little aluminum keys with instructions from Autozone just for this..

Originally posted by 90rocz
Sounds like an "ignition timing" or a "lean condition" rattle, either caused by overheating, or clogged fuel filter, dying fuel pump etc...If you can pull up the codes by using the Assebly Line Diagnostic Link (ALDL) it will be really helpful...You used to be able to get little aluminum keys with instructions from Autozone just for this..

Definately Pinging.....I hope you are running 92+ octane fuel. If so you need to check your timing. Might need to back it down. My ole' L98 di the same thing. I accelerated and the pinging started then all of a sudden Check light comes on. Good news is that if you reset computer, your car should run like it did.

PINGING!!!!!

Later

I am just running 87 fuel. Next time I am in shop class I will check my timing though. To reset my car I just pull the negative cable off for a while and then hook it back up right??? Also can I check codes while the engine is running by using the paper clip method???

There is a tan wire, possibly with a black stripe by the Strut Tower area that has a GM Weatherpak connector. When the car is warm, disconnect that and take the timing. NOTHING to do with the battery cable.

I will be able to check my timing and such on Wed. I just changed my fuel filter 2 or 3 months ago so I don't think it is that. Maybe my fuel pump is going bad, but my car doesn't take a long time to start??? What would cause my timing to be off?? I haven't done anything to affect the timing.

Hook a gague to the schraeder valve on the driver side of the fuel rail. Take off the hose to the FPR and you shoudl get about 44-45 psi of pressure.

Anything could cause your timing to be off. Hard to say what would make the bolt come loose but check it and let us know.

Yea the computer definetally should store the codes....Are you sure your waiting long enough? It will flash 12 x 3 times announcing start of the test. Then it will flash each of your codes 3 times after that and then it will flash 12 x 3 times again as the end of the test.

Run premium fuel and your troubles will disappear.......It even states in the manual to run nothing but premium (92+) in your motor.

You have a sports car/ muscle car......You have to pay to play.

Later

Can I check the codes while the engine is running???

Originally posted by 1fastformula
Run premium fuel and your troubles will disappear.......It even states in the manual to run nothing but premium (92+) in your motor.

You have a sports car/ muscle car......You have to pay to play.

Later

I don't think that is the answer. Looks more like a band-aid solution to me. LB9 and L98 which are both TPI 305 and 350 respectively require premium unleaded while LO3 which is the non-TPI 305 requires 87 octane. So, you need to find out what is causing it instead of just dumping premium fuel and band-aid the problem. This is per the owner's manual.

Well driving around tonight in the rain the rattling wasn't as bad. It was also colder out. I really think this might be just exhaust but I am gonna check my timing out anyway. Thanx for all the help guys.

Well I have a new thought on what this might be. Today I was driving around kinda hard and the rattle started then my check engine light came on. When I pulled into my driveway I got out and just listened at different parts around my car. Well right by the cat it sounded like the car does after you turn it off and it is cooling down. That metal shrinking time sound except the car was still running. Could it be stuff inside my cat breaking up??? I don't think that cat has ever been replaced.