HELP! Engine rattle/knock worsening since fuel additive/premium ga Options

[celicakitten]

Please help with any input as I'd like to get the knowledge of people who really know these cars! I just bought this car and am discovering some issues(as expected) that I'd like to sort out before going to the dealer or hopefully finding a good local mechanic to help me!

Here are some stats before I describe the main issue:

-97 Celica ST 5spd Stock-original engine/transmission
-192,xxx miles
Guy I bought it from recently replaced the:
-timing belt
-spark plugs/wires
-distributor(looks fairly new at least)

Everything works, passes emissions, shifts great, and idles perfect other then a little vibration when the air is turned off. What my main concern is that initially there was a slight rattle/knock on start up and occasionally at higher speeds(inaudiable if the radio was even slightly on). I tried to chalk it up to the bar that holds the hood up as the clip to hold it down in place was broke. 2 days ago I topped her off with 91 octane and a bottle of chevrons fuel system cleaner, and on day 1 the car seemed to respond quickly and perform even smoother.

BUT...

On day 2 the rattle/knocking noise became more apparent continually getting louder (although my paranoia/turning off the radio may also play a part), and is now almost constant! Only time I don't hear it is when the car is idling. I drove it 14 miles each way to work and back(mostly freeway) for 2 nights, and as of this morning I fear to drive it if there is a real issue with the engine. I put her in neutral and pulled the throttle to try and verify that the engine is making the noise...there's slight noise on the rev and then knock knock knock back down to a quiet idle. I had to replace the motor mounts on my old celica and this is nothing near the same noise, so I'm almost positive it's not that. When the engine cools off I will inspect the spark plugs/wires/wiring...maybe distributor? I'm afraid too many deposits have been loosened, but am curious if it could be anything else and what/if anything I can do to fix it!!! I know it's an old car and there's a good chance it may be the engines time...but I really hope not! I'd like to minimize my expenses until the time is right for an engine swap and still use this car as a daily driver around town. Any help or suggestions would be greatly appreciated!!! Thanks in advance!

This post has been edited by celicakitten: Jun 3, 2012 - 11:21 AM

[Special_Edy]

Ok, the spark plug wire situation could very likely cause the knocking noise, and it could definately cause a misfire which would make smelly exhaust, loss of power and lots of vibrations at idle. You need to get them replaced. Spark plug wires for my '94 with a 5SFE cost me about $45 with a lifetime warranty at autozone.

The missing bolts on the manifold heat shield will cause it to rattle. The heat shield will rattle at random rpms and I dont know how to explain the sound other than it will sound like a cymbal from a drum set being hit very rapidly.

Finally the crack in the manifold will make a knocking sound. You may be able to get someone to weld it back together for cheap without needing to remove it.

[Xander_X]

Ok, the spark plug wire situation could very likely cause the knocking noise, and it could definately cause a misfire which would make smelly exhaust, loss of power and lots of vibrations at idle. You need to get them replaced. Spark plug wires for my '94 with a 5SFE cost me about $45 with a lifetime warranty at autozone.

The missing bolts on the manifold heat shield will cause it to rattle. The heat shield will rattle at random rpms and I dont know how to explain the sound other than it will sound like a cymbal from a drum set being hit very rapidly.

Finally the crack in the manifold will make a knocking sound. You may be able to get someone to weld it back together for cheap without needing to remove it.

What Edy said, except I'll add this:

I personally don't like aftermarket plug wires. After 12+ years of working on Imports (I also went to Toyota's mechanic school for 2 years), I found that vehicles like Honda and Subaru don't really like aftermarket plug wires all that much. They're very finicky. Of course T-Ten (toyota school) will teach you to ALWAYS use OEM parts. This is my first Toyota I've owned that I've really played with (I went straight to working at a Honda dealership out of T-Ten school and always tuned Honda's and Subaru's) so I don't have the experience with them as much as many on this forum, but they are designed very similar due to competition between makes, available technology and just plain physics. I would always buy OEM plug wires just due to past experiences. One of the reason Toyota, Honda and Subaru are so much better than most other makes is everything is mathematically precisioned and tolerances are tight. There isn't a lot of room for error. They're more expensive, but you'll never have a problem with them (the OEM wires I mean). Just my opinion. I know PLENTY of people have great success with aftermarket plug wires, it's just one of those parts I'm biased against the aftermarket.

With the crack, you can probably get it fixed. Or replace it with another one from a junk yard. If your planning on doing some mods, I would use the opportunity to get a performance header and exhaust. There are many post about these if you want more info. The consensus seems to be that most performance headers are "ebay specials" yet most reviews are positive so I wouldn't hesitate using one. And most people tend to get the rest of the exhaust custom made as the few companies that make full systems for the 6gc are quite pricey (over $1000). I would recommend a full 2" exhaust with a resonator. Magnaflow makes an inexpensive 2" cat. The 2" with give you enough flow to gain a little more flow without taking away too noticeably from your low end torque. I suggest a resonator just for the purposes of toning down the noise so it doesn't sound like a Ninja 10R driving down the street.

This post has been edited by Xander_X: Jun 5, 2012 - 11:39 AM