Toyotaman larry need help

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  #1  
Old 08-09-05, 06:19 AM
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Toyotaman larry need help

Larry my wifes 2000 Toyota 1.8l needs your advice.I wrote to you before about a multi cyl missfire code it cleared by itself.Anyway I figured out why it trips.
When engine is cold and A/C switch is left on car runs real rough and CEL light comes on.With A/C off idle is smooth.I have to let it run for a few min before turning on A/C so CEL does not trip.
My 2004 Tacoma does not do this nor has any other Toyota I have owned.
It is more of a inconvenience because I have to drive around with a CEL light for a few days till it goes off on its own.
What do you think?
Only runs rough when engine is cold with A/C on.
 
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  #2  
Old 08-09-05, 01:42 PM
Join Date: Jun 2002
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Never come across that one.

Cover the basics, Use 87 octane, OEM plugs, Clean air mass sensor.

Possible A/C overcharge?
 
  #3  
Old 08-09-05, 05:03 PM
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Might be a good idea to see what the code from the CEL is - this may point to the problem. I know that in my car when the A/C is switched on the control module on the compressor sends a signal to the engine computer which then sends a signal to the IAC control valve to increase the idle speed to prevent rough idle due to the additional load on the engine. If you car has such a system and it is malfunctioning then you could get this symptom.
 
  #4  
Old 08-10-05, 06:24 AM
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same code

same code P0300 random misfire goes away and only comes back when car is started with A/C on (engine cold only).car only has 40 something thousand miles and plugs are the iridium big bucks type supposed to be good for 100 thousand.Only use 87 octane air filter is clean I guess I will try to clean the air mas sensor is that the same as the MAF sensor?A/C never been serviced since bought from dealer as certified and it works good.Maybe I will have to just train the wife to turn off air before shutdown .
What is it that kicks up the idle whith air on on these newer cars?I recall older cars had a soielonid .
 
  #5  
Old 08-10-05, 10:20 AM
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Yes MAF. ECU controls IAC to raise idle. Quick check of IAC is to see if RPM surges to 1100 or so on start and returns to normal idle. If it starts and goes to normal idle speed it's sticking.
 
  #6  
Old 08-10-05, 04:55 PM
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one more question

Will the engine rpm go up to 1100 rpm with engine either cold or hot and then drop?
 
  #7  
Old 08-10-05, 05:05 PM
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I guess your service manual (if you have one for the car) should tell you if such a system is in operation, how it controls the idle etc. It is possible (depending on the design/program in the engine computer's microcontroller) that the misfire code may be set if the computer is expecting the idle to be higher but the actual idle does not match the expected idle.

If the control is indeed via the IAC valve the thing to check would be the control voltage to it when the AC is swicthed on. Again hopefully your manual should tell you what to expect. Unfortunately if the control signal is pulsed (like PWM) you will need an oscilloscope to see if the pulse widths actually change. If the control is ok then the valve may be sticking as mentioned.

I guess the idle should be higher with the A/C on and engine cold and should progressively drop to normal idle when it warms up.
 
  #8  
Old 08-10-05, 06:08 PM
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It is possible (depending on the design/program in the engine computer's microcontroller) that the misfire code may be set if the computer is expecting the idle to be higher but the actual idle does not match the expected idle.
ECU measures time between crank pulses against crankangle sensor for misfire. Will not be set if idle is not at target, thatís a separate code.
 
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