RPM decreases to idle
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This is a discussion on RPM decreases to idle within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hi. I have a 2001 WRX. I change standard pistons with forged ones. After this I start the engine, let ...

  1. #1
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    RPM decreases to idle

    Hi. I have a 2001 WRX. I change standard pistons with forged ones. After this I start the engine, let the car warm up, and then turn it off, wait for it to be cold, and refill coolant. Now I start engine, let it warm up, and then rev it to 4000rpm, but about 2 minutes after the rpms fall to idle and then keep balancing between 500 and 1500 rpms until I lift my foot from accelerator and then if I accelerate it goes again to 4000rpm for about more 2 minutes and then it fall again to idle rpm and so on so on... What could be wrong.

    Thanks
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    Registered User EvoEatr's Avatar
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    I would double check everything they/you pulled off which is like everything because obviously the engine came out...does the car idle normally at all? with the engine running I would spray some gum cutter (2+2) around all the intake gaskets and vacuum lines and see if the idle fluctuates at all...Any CEL on or codes? Have you taken it for a drive yet and get it up to operating temperature? Automatic or manual trans? How many miles are on the car? any other mods besides the forged pistons? Im assuming you used new head gaskets and intake manifold gaskets and everything correct?

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    Hi. Idle is normal. No error codes. Head and intake gasket are new. Head gasket was choose according to the pistons to maintain compression ratio. I have not yet taken it for a drive.
    If I accelerate below 3500rpm it runs normally. This only happens above 4000rpm. I had a pc connected to OBDII and monitoring and nothing strange came out.

  5. #4
    Registered User EvoEatr's Avatar
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    Have you checked the IACV? sometimes they get carboned up and cause odd idle problems..

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