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I have a 2002 mazda 626 with 145,000 miles. It has a rough and fluctuating idle. Sometimes it will be very low (around 500-600 rpm) and others sky high (2500+ rpm) and just keeps climbing until i turn on the ac or put the car in gear (which is very harsh). I have replaced:
Intake manifold gasket
Coolant temp sensor
Cleaned egr and passages
Cleaned throttle body and iacI have an issue where i believe the thermostat is stuck open because the engine is never up to operating temp. It is always very close to cold. I plan to fix this soon but my main issue is that i think i may have narrowed it down to being the throttle body. It is very sensitive to touching. The idle can be very low and almost stall but if you place your finger and touch anywhere on the throttle body, the idle gets high again.. Any ideas?
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Replies
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If you have a scanner read live data engine coolant temp
to see if you are coming up to temp vs your gauge. or use
an infra red thermometer. Fix the temp issue and go from
there.I would look at the Throttle Position Sensor (TPS). You can test this by just unplugging the TPS, if you car starts running better you may have a bad TPS. You could also have lost the 5v reference voltage which could also cause the same problem. You can back probe the TPS to verify you have a 5V reference voltage.
If the engine isn’t coming up to temp that can effect the idle. I would resolve that issue first and then see if you still have an idle problem. I do not recommend messing with the TPS unless you have some evidence that it’s an issue such as a CEL with a code for the TPS.
Lastly, don’t forget to bleed the cooling system after you replace the thermostat. Failure to do so can cause overheat and engine performance issues. More info here.
http://www.ericthecarguy.com/faq/solving-automotive-idle-problems
Keep us posted.
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