1997 Toyota tercel gas consumption issue

Old 03-13-13, 08:51 PM
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1997 Toyota tercel gas consumption issue

I have a 97 tercel with 230000 miles that is suddenly running about 17 mpg. It is an automatic, 4 cylinder. Last year I had an issue with engine misfires. I changed the plugs and wires. Ran fine for a bit and then misfired again with higher speeds. Coils were replaced and the car ran ok for two weeks then misfired when speeding up to excess of 45 mph. Found out I had carbon buildup on valves causing misfires on cylinders 1 and 3. The carbon was cleaned off and no more misfires have occurred. Had a fuel system cleaning and car runs without skips or misfires but is now consuming a lot of gas. I have had a problem with carbon buildup on the spark plugs indicating a lean condition, but without a check engine code, I'm not sure what my next step should be. I feel as though the carbon buildup is a symptom of a much larger issue. I know my car is high mileage, but I have taken care of it and think it still has life left in it, and advice would be very much appreciated!
Old 03-14-13, 08:55 AM
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Carbon buildup on the plugs does not indicate a lean condition. It is usually the result of excessive oil consumption. An engine with this many miles is not going to operate as efficiently as it once did. Short trips also will cause the problems you describe.
Old 03-14-13, 11:31 AM
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There are a few other things that can cause carbon build up, such as old worn plug wires, old plugs, as well as not enough highway driving . Even a trip out the highway and accelerating rapidly ( and safely) to get up to speed can help reduce carbon biuld up. There were many a K-car with the 2.2L engine that had the same problem because they were usually owned by older , easier drivers and that engine needed to be revved out once in a while to avoid carbon build up. I've had them come in for a second opinion having been told they needed a valve job due to carbon build up. I simply ordered "Combustion Chamber cleaner" from Chrysler dealer, as I always found it worked best. Follow directions on the can and allow to sit overnight if you can. Have 4 new spark plugs ready to go in after, as I've had the porcelain around the tips, come off with the carbon before as well. Start engine next morning as directed and rev at a safe rpm, to clear all that crap out, then after, install new plugs. You should see quite a difference. Then try too get in the habit of "flooring it" until up to speed, and let engine rev out once in a while, it really will help clean that carbon out of there. A new set of wires wouldn't hurt if they are old as well. Speak to parts guy as well about going up to a hotter plug as well, maybe one or 2 heat ranges if you do a lot of city/town driving. That helps burn carbon off better as well.
Old 03-14-13, 08:15 PM
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How do you know you have excessive carbon buildup? Did a mechanic tell you?

The same mechanic who said it was caused by a lean condition?

How did you clean the carbon off the valves?

Do you have excessive oil burning?

Sounds like someone is mis-diagnosing things and throwing parts at it to no avail.

Good luck.
Old 03-15-13, 05:10 AM
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I would be inclined to get it on a scanner to see what's happening in real-time and I would throw in a compression check just to see how the top-end health is. I also echo the comment about a lean condition showing carbon.
Old 03-16-13, 04:04 AM
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In addition to what's been posted already, 230.000 miles is not a great amount of mileage. On the other hand, it is enough mileage to warrant the tests below. You should do these tests and post the results.

Cylinder leak down test

Engine vacuum pressure test

Fuel system pressure test

Exhaust system pressure test

Also Auto Zone does the scans that show the presence of any error codes. They do these scans for FREE, so you have nothing to lose. Have a scan done at an Auto Zone Store, and post any error codes that the scan finds, so we can see them.

Thank You

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