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Discussion Starter · #1 ·
I have an 87 n/a and recently it started idling weird. This happens randomly and not just when engine is cold. The car will idle around 900-1000 rpm normally but has started revving. Not high, but to about 2k, then drops. It keeps doing this and then just goes back to regular. I've tried searching it, and see that it may be the IACV, but wanted to ask the group before I start chasing this demon. The car is all stock, with no performance parts added. Any info would be greatly appreciated.
 

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I don't think anything is wrong with the IACV, but it does use the coolant to measure the engine temperature. Likely there are air bubbles in the coolant, and when a bubble gets into the valve, it switches to cold idle. When the idle gets too high, the ECU cuts fuel, and the cycle repeats until the bubble moves on. This is a common malfunction. Search for "bouncing idle" or "zooming idle."
 

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Red Mk1a Mr2
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I had this same issue and it was due to my IACV being stuck open / inoperable, my TPS sensor was not in the correct position and my throttle plate was slightly open at idle. I would suggest removing the throttle body and inspecting it closely for any of the issues I mentioned. More often then not I find that @rmeller is pretty spot on with his two cents so I would check and perform a air purge of the cooling system prior to taking apart stuff.
 

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Filling the reservoir is not enough. There is a procedure for purging the air bubbles, and I suggest that you use the BGB and do it by the book. The low coolant suggests that there is a leak, and the leak will introduce air even if the coolant has not fallen below the suction tube.
 

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Discussion Starter · #6 ·
I plan to go over it all this weekend. I was just adding the coolant bc I noticed it was low when looking for anything loose after work. I'm new to mr2's, so thanks for mentioning the bgb. I was able to download a pdf of it. Going to look through it bf starting on the car. I appreciate the info.
 
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