Not constant idle

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timnutt
Posts: 119
Joined: 03/07/17 15:14

Not constant idle

Post by timnutt » 14/07/19 19:29

Hi,

Once my Mk2 Rev2 Turbo gets up to temperature it doesn't have a constant idle. It will blip upto 1200rpm and then back to 800rpm every second - really annoying when sitting at traffic lights. I'm guessing the ECU is getting conflicting information from sensors. Any ideas how I can troubleshoot this or fix it?

Thanks
Tim



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abovetherim
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Re: Not constant idle

Post by abovetherim » 14/07/19 22:20

Common problem on Toyota's is the idle air control valve IAC, can get gunked up.
YouTube it to show how to clean/test.
Just remember to spray a little wd40 in there after cleaning with carb cleaner to help the gate bearings stay lubed otherwise it could stick again in a month or so.

If that doesn't sort it inspect all vac hoses as a vac leak can also cause hunting.

Has the intake or throttle body been removed recently? If so did you replace the the gaskets and are the bolts torqued up fully as both can vac leak.
1991 rev 1 T Bar n/a 3sge import. A work in progress!!!


Topic author
timnutt
Posts: 119
Joined: 03/07/17 15:14

Re: Not constant idle

Post by timnutt » 16/07/19 12:02

Thanks for that.
I disconnected the plug to the IACV to see if that made an difference, but sadly it didn't. Am I missing something here. I would have thought that disabling it completely would stop the fluctuating idle.

So I plugged it back in, restarted the engine and I ran it up to temperature while I checked a few other things. I then restarted the engine and it ran fine (albeit a slightly high idle of 1100rpm) - but no fluctuations.
I'll look for any vac leaks, but it seems inconsistent :-(

Thanks
Tim

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abovetherim
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Re: Not constant idle

Post by abovetherim » 17/07/19 20:10

As part of the idle control the ECU modulates the gate in the IAC valve to maintain the correct air with the throttle plate closed. (Make sure the throttle plate and tb wall are clean)

If the IAC is gunked up the ECU can only modulate the fuel hence a cause of hunting.
I believe on the turbo you can get to the 2 screws on the front of the IAC. Using a well fitting screwdriver undo those and take off the magnet. This will reveal a shaft you should be able to twist back and forth really easily. If it's got any drag pull off the tb and remove and clean the IAC.
1991 rev 1 T Bar n/a 3sge import. A work in progress!!!

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