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95 Sc300 Troubleshooting Assistance Requested.


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1995 SC300 with about 132K miles.

In the last 6 months I have replaced or changed:

Timing belt/Tensioner, water pump

Serpentine Belt, tensioner pulley.

Alternator

Plugs, Wires

Fuel Pump, Fuel Filter

Now the symptoms:

1. Start the car, from cold no problems at all, runs great, no miss, no hesitation.

2. As the temp starts to climb toward normal the problems start to increase. The engine runs rough, doesn't want to rev, has no power and develops a miss that gets worse the higher the temp gauge climbs. The car doesn't over heat, but once it gets to normal operating temp it is impossible to drive. The miss gets so bad it sounds like it's back firing through the throttle body. Eventually at full operating temp it won't even idle and the miss is horrible.

It's been suggested to me that it may be the crank position sensor or clogged cats. It's also been suggested that it could be one of the two temp sensors.

I don't want to ditch the car, but I also don't want to start replacing every sensor on the dang thing because knowing my luck I'll have to replace them all, and it'll be the last one I replace that will cure it.

I've had another car with a clogged cat, and it did something similar, but it feels like there's decent flow out the exhaust tips even at full temp.

I did a compression check, and every thing looked good on all 6 cylinders. The plugs looked fine but I replaced them anyway. I haven't noticed any raw gas smell, or any smoke from the exhaust.

My gut instinct (from other car problems) says that the computer doesn't seem to be adjusting the timing correctly. Almost like it warms up and looses it's mind.

But, at this point, I'm stumped. I'm also 90 minutes from any Lexus dealership, and my local Toyota dealer looked at me like I had sprouted horns when I took it there.

Any help or ideas would be appreciated greatly.

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  • 3 weeks later...

1995 SC300 with about 132K miles.

In the last 6 months I have replaced or changed:

Timing belt/Tensioner, water pump

Serpentine Belt, tensioner pulley.

Alternator

Plugs, Wires

Fuel Pump, Fuel Filter

Now the symptoms:

1. Start the car, from cold no problems at all, runs great, no miss, no hesitation.

2. As the temp starts to climb toward normal the problems start to increase. The engine runs rough, doesn't want to rev, has no power and develops a miss that gets worse the higher the temp gauge climbs. The car doesn't over heat, but once it gets to normal operating temp it is impossible to drive. The miss gets so bad it sounds like it's back firing through the throttle body. Eventually at full operating temp it won't even idle and the miss is horrible.

It's been suggested to me that it may be the crank position sensor or clogged cats. It's also been suggested that it could be one of the two temp sensors.

I don't want to ditch the car, but I also don't want to start replacing every sensor on the dang thing because knowing my luck I'll have to replace them all, and it'll be the last one I replace that will cure it.

I've had another car with a clogged cat, and it did something similar, but it feels like there's decent flow out the exhaust tips even at full temp.

I did a compression check, and every thing looked good on all 6 cylinders. The plugs looked fine but I replaced them anyway. I haven't noticed any raw gas smell, or any smoke from the exhaust.

My gut instinct (from other car problems) says that the computer doesn't seem to be adjusting the timing correctly. Almost like it warms up and looses it's mind.

But, at this point, I'm stumped. I'm also 90 minutes from any Lexus dealership, and my local Toyota dealer looked at me like I had sprouted horns when I took it there.

Any help or ideas would be appreciated greatly.

Almost sounds like when I had to change my head gasket. Have you checked your coolant for any tell tale signs of oil? When it came close to failure, there always seemed to be a bubble trapped in the Coolant lines and I had to run it with the cap off til it released. Dont know why the toyota dealership looked at you funny, it is a NA supra and all share the same symptoms.

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