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This is a 2009 1.8 Corolla with 150k km on the 2ZR-FE engine. At idle RPM's cycle up and down by one or two hundred RPM and there is a gasping or rotational noise from the right hand (belt) side of the engine. The noise seems to cycle on and off around every second there's a short video here, it's a hard to hear but the RPM can be seen changing.

I run a smoke test on the intake with no leaks, the PCV valve is clean & rattles nicely, the intake manifold gasket is good. There are no check engine codes otherwise the car drives nicely at all speeds. I don't think this model has an intake air control valve as the throttle is drive by wire. Long term fuel trim's 0%, the short term moves around a couple percent positive and negative.

EDIT 2019/06/05 MAF sensor cleaned, injectors all have the same resistance, problem remains

EDIT 2019/06/06 Brake booster vacuum check valve tested with no problems, ran idle relearn by turning key a couple of times before starting. At the moment the noise is most present in drive or park whilst idling at traffic lights with the engine fully hot.

EDIT 2019/06/11 Ordered a new water pump to replace the original which may be causing the noise described, will report back in a couple of weeks. Regarding the RPM fluctuation one friend thought this was a faulty gauge on the instrument cluster.

EDIT 2019/06/23 changed out the water pump and gasket, no change to the symptoms

EDIT 2019/06/24 Seems the fluctuation and noise could be separate. A local mechanic thought the gauge movement was an instrumentation problem. Of course the engine didn't make the intermittent noise at that time. We managed to grab a another recording of the noise.

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  • Have you tried an idle relearn? Can you track down the noise? – Ben Jun 5 '19 at 1:16
  • @Ben yes tried a couple methods from youtube by fully draining battery and also rotating the key a couple times and idling in drive – ajayel Jun 5 '19 at 22:21
  • On toyotas to do the idle relearn. Pull the etcs fuse. Disconnect the battery short the leads together for 10 mins. Clean the throttle. Put fuse back in. Hook up your leads. Key to on 10 seconds. Start and idle 10 mins or so with no loads on. – Ben Jun 6 '19 at 1:48
  • Thanks for explaining that @Ben, just did the procedure idle still fluctuates, wish I could figure where the noise is coming from. – ajayel Jun 6 '19 at 4:41
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    Maybe remove the belt and see if it still makes noise and the idle continues to fluctuate. – Ben Jun 6 '19 at 14:29
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After doing some more deeper research on the drive by wire system. I discovered that you were correct about not having a idle control valve. That is for mechanical operated throttles.

The drive by wire system uses a small motor to actuate the throttle plate based on accelerator input by the driver and uses a variety of sensors to determine throttle angle, air fuel mixture, etc.

https://youtu.be/Pgln9L5Y7sQ

The options for correcting idle issues with a drive by wire system is to clean or replace throttle body followed by a reprogramming (recalibrating) the ECM and resetting the idle using a scan tool. The process takes about 20 minutes. Then you drive the vehicle around to further reeducate the system. Afterwards the engine will purr like a kitten and great fuel economy. I had this done recently myself.

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  • Unfortunately this car doesn’t have an IAC valve, as mentioned above it has the electronically controlled drive by wire throttle – ajayel Jun 3 '19 at 19:56
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The fluctuating/noise problem seems, five points something :

1) Check for the clogged fuel filter/stainer inside and outside the fuel pump/injection system. And also inspect the fuel lines, the fuel pressure and the fuel quality.

2) Clean the air filter and throttle body parts.

3) Inspect the purge control system functioning.

4) Carefully check for the leaks in exhaust pipes, near heated oxygen sensors.

5) Test for the loose ground connections and visually inspect for any corroded/rotten wires, terminals and connectors.

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Resolved (so far :) - last week replaced the timing chain tensioner (Toyota OEM #1354037030). The noise at low load is now gone and the RPM needle remains steady at idle. Anyways I'll accept this answer after a month should this solution stay stable.

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