Questions and Answers
I own a Mazda 626 1990 model. It has a 2.2-liter engine fuel injected with P/S A/C and cruise control. When the car is at normal operating temperature the idle fluctuates about 200 rpm up and down while I am at the lights.
Mazda 626 Idle Bounces
Q. Hi Vince, before I say anything else I would like to congratulate you on your commitment to this site. I think it is great that you offer such a great service to the public for free.
Also, if the engine is at normal operating temperature and it is idling the idle speed drops slightly and becomes rough when I use the power windows or the heater fan or the headlights or the rear demister or anything else electrical. It soon returns to the normal idle speed after about 2 seconds. Could these two problems be related? Could it be the idle speed control valve or something?
I am not much of a mechanic so I wouldn't know. Any help that you can give me would be greatly appreciated.
Thanks in advance,
MatthewA. Thank you for the compliment. I try to provide as much information as I can and I'm glad you find it useful.
It could be the Idle Speed Control valve (ISC). After engine warm-up, the ECU controls the ISC valve to maintain good idle quality under a wide range of operating conditions. It is possible this valve is bad or just dirty.
It is also possible that one of the inputs to the ECU is bad. Since there are about 11 inputs widens the range of possibilities further. Things like intake air temp sensor, throttle sensor and water temp sensor, among others. There is also an engine load sensor that could be bad. This senses additional loads such as A/C, power steering and alternator demands, sends the signal to the ECU and in turn the ECU raises the idle speed to compensate for the extra load.
I would try cleaning first. Take off the air intake hose at the throttle body and give it a good cleaning with carburetor cleaner. A lot of times this will cure the idle fluctuation and if not, the most efficient way to determine where the problem is is by checking the inputs and outputs checked with a scan tool.
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