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?

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.

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.

if you can get one to try cheaply, worth getting another tb.

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.

hmm check eper ?

yes, i know i know - i even have a much newer eper than whats on here, that requires effort though lol

blu73 said:

yes, i know i know - i even have a much newer eper than whats on here, that requires effort though lol

Click to expand...

same same, i never knew how to use eper haha !

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

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

so you are using the 1.6 tb?

What's an IAC?

Idle Air Control, or commonly called an ICV (idle control valve)

ycming said:

so you are using the 1.6 tb?

Click to expand...

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.

mrcinquecento said:

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.

Click to expand...

is idling like hunting, goes down and up and repeat? And black stuff comes out the exhaust ?

I wouldn't say it was hunting as such it seems to want to idle where it should be, but yeah it's a repetitive miss/dip at idle when hot and i seemed to get black stuff out judging by my backboard in the garage!

I have somebody visiting me with a similar problem on Sunday, and we will try to look for the solution. You say that swapping over 1.6 tbs did not help, I got it right? Disconnecting lambda helps? If so, how old is the sensor? Do you have the charcoal canister mounted / connected? No leaks in the inlet?

Sorry for asking perhaps stupid questions, but I will be checking all this myself and perhpas you can give me a headstart

Hi

Yeah swapping the 1.6 tb for the 1.2 tb made no difference.

Unplugging the lambda seemed to help a little, the dipping seemed to take very slightly longer to happen, only started to come in at just over 80-85 degrees showing on coolant temp but still did it eventually. I then reconnected the lambda and it seemed to smooth it out a bit better than before, it was still doing it but the pop from the exhaust wasn't as harsh and it didn't seem like the idle was dipping quite as far when it did.

My sensor isn't exactly the newest, it's at least 5 years old, was on my 8v but hasn't ran much in that time before it died, wouldn't surprise me if it wasn't healthy given the 8v died with piston rings. But when it went in for an mot as a 16v recently, the lambda test was passed, so it is still doing something. Considering getting a new one to test along with swapping the map over to test.

I don't have the charcoal canister and afaik my inlet is leak free, Had new gaskets and all bolts are in and torqued up and no other obvious running issues bar the idle dip when hot and emissions test showing rich running, which is certainly the case given the pop when idle dips and small amount of the black sooty type stuff from the exhaust.

The problem with the 16V ECU is that disconnecting the oxygen sensor does not necessarily disable the lambda correction. My 16V patient has a "lazy" sensor for sure, hardly manages to activate the correction.

Did you try checking the diagnostics parameters with IAW ECU Scan 2 while this happens?

I haven't ran diagnostics as yet. Need to order leads.

On the emissions test, whilst it passed on the lambda it only just passed on it, so knowing the age and history of the sensor, it's pretty much at the top of my list of suspected causes, it clearly still does "something" given the small difference in that idle dropping when connected, but i'm not convinced it's quite doing things well enough or fast enough, which i would suspect could be the cause in the drop of idle/overfuel if it's "lazy" and messing up parameters.