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Old 02-07-2014   #1
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16v hot idle

Evening all, soon time to put in my 1.2 16v cinq for an mot but have an emissions issue and reckon a problem on hot idle is what's causing it (or at least a symptom of it).

From cold, it idles beautifully. It's silky smooth. As it gets hotter and the idle revs dip, that's when problems start to show, the revs drop to about 875rpm fine but every so often they will try to drop down/stall attempt but it gives a small pop in the exhaust like an overfuel stutter and the revs rise back up to around 875 rpm. Given there was an overfuel in the emissions last time i figure it's connected.

Any idea of likely causes?

Given it seems to be temperature related, i changed the blue coolant temp sensor for a known good one but that didn't work. Map sensor seems to be working fine from what i can tell given it runs horrible without and pretty much tries to stall, then when you reconnect it running, it sometimes does.

Today took the throttle body off and my idle control valve seemed a bit gummed, so cleaned it up thinking it was perhaps sticky so slow to react, seemed to free it off and when i started it with the valve opened, it took 4 or 5 start attempts for it to adjust and re-set itself without revving it's nuts off at idle, so possibly still sticky and not reacting to any changes when it's up to temp?
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Old 03-07-2014   #2
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Re: 16v hot idle

Not sure which 16v you have, but isn't the ECU coolant temp sensor green?

Could be IAC -- currently my MR2 is playing similar silly buggers.
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Old 03-07-2014   #3
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Re: 16v hot idle

It's blue, same as the 8v, same sensor and same plug on the loom

Think i might take the throttle body off again and have another poke about with the iac, seems to be moving freely enough bit given how reluctant it seemed to reset itself when refitted, i'm not convinced it's working 100%. Also when i switch the car off it makes a strange gurgling buzzy noise from the iac for a couple of seconds, about 15 seconds after the engine is shut down, not sure if that's normal or not or a sign of something struggling or even failed. Noise is a little similar to the fuel pump priming, but from the IAC after a run.

The fact it did adjust the idle...eventually makes me think it does fundamentally work though in that it does move, just perhaps not quite at the speed it needs to.

Everything else i can think of seems ok, lambda passed on emissions test so suggests it's doing something at least, Crank sensor doesn't seem too likely given it seemingly runs fine off of idle, reckon the car needs a good "Italian tune up" because the ecu might still need to re-learn, plugs look fine bit going to swap them anyway to help emissions for the test etc.
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Old 03-07-2014   #4
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Re: 16v hot idle

if you can get one to try cheaply, worth getting another tb.
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Old 03-07-2014   #5
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Re: 16v hot idle

Does anyone know if the IAC and TPS are the same as the ones on the 8v TB's. They look the same as far as i can tell. Been wanting to try swapping them on mine (unrelated issue sorry to hijack a tad). Just i have a few 8v TB's i could steal them from if the same, cheaper and easier than going and finding another TB.
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Old 03-07-2014   #6
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Re: 16v hot idle

hmm check eper ?
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Old 03-07-2014   #7
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Re: 16v hot idle

yes, i know i know - i even have a much newer eper than whats on here, that requires effort though lol
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Old 03-07-2014   #8
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Re: 16v hot idle

Quote Originally Posted by blu73 View Post
yes, i know i know - i even have a much newer eper than whats on here, that requires effort though lol
same same, i never knew how to use eper haha !
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Old 03-07-2014   #9
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Re: 16v hot idle

its really easy if you use your vin number, but us lot with engine conversions don't have the correct vin for the engine parts. But i will look them up later
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Old 03-07-2014   #10
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Re: 16v hot idle

Not sure about 8v, but i can tell you the iac at least is different between bravo/brava 1.6tb and punto mk1 1.2 16v tb, it's held in by torx on the 1.2 and forced onto the 1.6 body

I've 2 spare 1.2 16v tb's but the throttle cable bracket is jammed onto my 1.6 one so it'd be annoying if it was needing a full time swap haha
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Old 03-07-2014   #11
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Re: 16v hot idle

so you are using the 1.6 tb?
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Old 03-07-2014   #12
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Re: 16v hot idle

What's an IAC?
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Old 03-07-2014   #13
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Re: 16v hot idle

Idle Air Control, or commonly called an ICV (idle control valve)
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Old 03-07-2014   #14
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Re: 16v hot idle

Quote Originally Posted by ycming View Post
so you are using the 1.6 tb?
Yup.

Swapped onto the 1.2 16v one for a test and it did exactly the same thing so swapped back. Seemed to smooth out without the lambda connected up but eventually started to do it again anyway. Reconnected it and after a run, it seems to be smoothing out a little, so hopefully it's just the ecu adapting.
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Old 04-07-2014   #15
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Re: 16v hot idle

Quote Originally Posted by mrcinquecento View Post
Yup.

Swapped onto the 1.2 16v one for a test and it did exactly the same thing so swapped back. Seemed to smooth out without the lambda connected up but eventually started to do it again anyway. Reconnected it and after a run, it seems to be smoothing out a little, so hopefully it's just the ecu adapting.
is idling like hunting, goes down and up and repeat? And black stuff comes out the exhaust ?
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