I bought a 1993 toyota corolla LE automatic with 106k miles on it last week. The car is only getting 20 mpg between city/highway and I am VERY easy on the gas. I have replaced the plugs, wires, distributor cap, rotor, pcv valve, fuel filter, air filter, used fuel injector cleaner, changed the thermostat and had the coolant system flushed. The car idles very smooth and runs great. The idle does fluctuate a little bit, but not a lot(maybe 100-200 rpms between hot and cold.) It seems to idle at around 650 rpm when warm and in gear. I have no check engine lights on. I have done some reading and suspect it could be the TPS sensor, or TPS sensor adjustment. I've also read the timing could be off a tooth, or that the egr could be the cause. Does anybody have any experience with this or have any thoughts? I thought I read somewhere that only the 1993 california model has an egr. Is this correct?
Any input would be greatly appreciated. Thank you
I'm not sure if this matters or not but I thought I would mention it. When I changed the plugs they looked pretty white(not the ceramic) like the car has been running lean. The tip on the rotor also was kinda white like it had been running hot.
Yes i agree check your tire pressure. It should be around 32 psi. While your at it, check your spare tire as well. I am not sure the exact psi on the spare but the driver side door panel should tell you
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Cars that I own:
1996 Toyota Corolla DX
1996 Toyota Camry LE
2007 Toyota Camry SE
I agree with bitter, the the O2 sensor may be a problem, but your very white plugs are an indication that your car is running very well. If it was the engine running rich they would be dark grey or black.
At this point I would check for fuel system leaks.
Just for comparison, I have a 95 wagon and I'm getting 30-35 mpg. I havent done any recent tune-up work.
Thank you all very much for your responses. As far as tire pressure goes I checked that within the first day of owning the car. The 02 sensor sounds like it might be a good place to look. What do you mean by the upstream one? I see online descriptions of front and rear, which one do you mean? Fuel leaks have also crossed my mind but the car leaves no puddles of any kind, and I don t see any traces of fuel under the hood. If the 02 sensor doesn't work I may take it to a mechanic and have him test the fuel system for leaks.
Last edited by mindbend1979; 11-24-2009 at 01:35 PM.
I was driving home tonight from Thanksgiving dinner on the interstate and suddenly my cars RPM shot sky high and it felt like the car had been shifted in to neutral because revving the gas would not engage the transmission. I coasted to a stop, put the car into park, then put it back into drive and the car shifted smoothly came right back up to speed and drove fine for the next 10 miles till i got home. I checked the tranny fluid, and the level was fine. I had the fluid(dex) and filter changed last week and it has been shifting great.... could the TPS sensor cause something like this. If the tranny had crapped out why would it go right back into gear, shift great, and maintain speed?
I forgot to mention that prior to having the tranny fluid and filter changed, that every once in a while the car would take awhile to decide to shift into top gear. That is what made me suspect a TPS sensor.
I'm surprised that nobody has mentioned to check the IACV (idle air control valve). Over time these get clogged with carbon, and cause the engine to produce a rough idle, surge, and/or idle up (amongst other things).
It's really easy to clean - All you have to do is take off the throttle body, turn it upside down, remove the 4-screws, and clean any deposits inside. It's also worth giving your throttle body a clean at the same time.
It not common for an IACV to fail completely, more often than not they just need a clean. Avoid using degreaser etc to clean it, proper electrical parts cleaner is the way to go. With a bit of luck it'll solve your problem - If not, then you can cross it off the list and move onto the next attempt.
Last edited by Kiwi-Corolla; 12-06-2009 at 08:33 PM.
I'm surprised that nobody has mentioned to check the IACV (idle air control valve). Over time these get clogged with carbon, and cause the engine to produce a rough idle, surge, and/or idle up (amongst other things).
It's really easy to clean - All you have to do is take off the throttle body, turn it upside down, remove the 4-screws, and clean any deposits inside. It's also worth giving your throttle body a clean at the same time.
It not common for an IACV to fail completely, more often than not they just need a clean. Avoid using degreaser etc to clean it, proper electrical parts cleaner is the way to go. With a bit of luck it'll solve your problem - If not, then you can cross it off the list and move onto the next attempt.
Thanks a lot for taking the time to write back. I really appreciate it! When it warms up again(its about 10 degrees f out right now) I will most definitely check out the IACV!
My car waits to shift into the highest gear as well.... but only when it is cold. The engine is trying to warm up.... even if it isn't cold outside!
Since my last post about the tranny. It has worked great since then. But when it is is cold outside my tranny will wait to shift into high gear too. That is why I still suspect the tps sensor. If it wasn't ten degrees outside I would be checking a few things. Also since it it has been getting cold, the idle will start out low and run rough, then jump up the rpm after 15 seconds and then it will go back down the rpm range when it warms up. When it is warm outside the car starts and idles smooth. It threw a Check engine light the other day when it was idling rough. After driving it to work(15 min)I shut it off and turned it back on immediately and the CEL went away and it idled smooth. I went to go check the codes but since i have a 93, I cant use a code reader. I did find a code reference guide and found out how to read the flashes though... we will see what that comes up with until thenn I'm guessing TPS.
On another note would anyone know off hand what belt might be squeaking when I press the accelerator? It only squeaks when i hit the gas.
I also have noticed that when i come up to a stop and the heater and headlights are on that the engine rpm drops kinda low and when i turn them off and on the RPM goes up and down. Any thoughts? I measured the battery voltage with the car off and it was 12.75. When i turned the car on with the radio, headlights, and heater on the voltage was 14.4, indicating that the alternator is working properly... am I correct? If anyone has any input on these issues I would greatly appreciate it.
Thank you all again for your responses so far! You have been very helpful.
I also have noticed that when i come up to a stop and the heater and headlights are on that the engine rpm drops kinda low and when i turn them off and on the RPM goes up and down. Any thoughts? I measured the battery voltage with the car off and it was 12.75. When i turned the car on with the radio, headlights, and heater on the voltage was 14.4, indicating that the alternator is working properly... am I correct? If anyone has any input on these issues I would greatly appreciate it.
Definitely sounds like the IACV - One of its jobs is to increase the engine's idle when under load (lights on, air con on etc). If the IACV is working correctly then your revs should drop when you turn your air con on, but should rise back to the normal level a few seconds later. If the revs don't rise then it's not doing its job properly. If the revs do rise back to normal, but the engine's revs surge up and down, then the IACV could be partially blocked with carbon deposits. Another good way to tell if it's working is to start your car on a cold morning and see if the auto choke works - This is another job of the IACV.
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1993 Toyota Corolla
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