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Discussion Starter · #1 · (Edited)
Hello all

I hope you dont mind me posting on here as I have a lotus elise. I've popped it into the MGF area as it seems the closest match. I was wondering if anyone could help me as I have a problem with my engine and no one on the lotus forums has any ideas yet.

When you blip the throttle, the idle will go down to either 1000, 1500 or 2000 rpm depending on how it feels. Sometimes in the higher rev ranges, when you come off the throttle the revs actually rise and then fall slowly. And sometimes all is OK. This is what I have tried:

-TPS reset - no difference
- Replacing TPS - no difference
- Replacing iacv - no difference
- checking for sticking throttle body - no its fine

The only thing that stops all of this is blocking off the iacv and the car runs fine. Obviously this is not ideal so I'm now wondering whats left to change. The ECU is definitely getting confused as to where the iacv needs to be.

Here's a video i took in the hope that it might help:

Video

You can just about hear the revs staying high and then slowly reducing then staying high for a bit more and going back to idle.

Like I say I hope you dont mind me posting on here but I am totally stumped

Thanks

Phil

BTW its a standard 1.8k but with a ported head and alloy inlet plenum
 

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Not sure if it's quite the same as the problem I had, but try getting some electrical switch oil spray from Maplin, unplug the ECU plugs and give them all a good spray. Also the plug that goes to the IACV.

Mine used to drive fine but the revs would just rise randomly at idle. Worth a go.

HTH
 

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Is it running rich at all. I'm thinking maybe the inlet air temp or coolant temp sensors. One thing's for sure, if it isn't mechanical, its electronic :doh: I'm guessing you've already polished up all the sensor plug contacts.
Not sure if it will be cheaper to gradually substitute new sensors or go for a diagnostic.
 

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Discussion Starter · #5 ·
Not sure if it's quite the same as the problem I had, but try getting some electrical switch oil spray from Maplin, unplug the ECU plugs and give them all a good spray. Also the plug that goes to the IACV.

Mine used to drive fine but the revs would just rise randomly at idle. Worth a go.

HTH
Thanks for the advice but I've tried that aswell. I've tried everything I can think of and nothing has worked!
 

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Discussion Starter · #6 ·
Is it running rich at all. I'm thinking maybe the inlet air temp or coolant temp sensors. One thing's for sure, if it isn't mechanical, its electronic :doh: I'm guessing you've already polished up all the sensor plug contacts.
Not sure if it will be cheaper to gradually substitute new sensors or go for a diagnostic.
I thought about the air temp one I must say but didnt really know how to check it? I think the water temp sensors are working as they should as when it is warm the tickover is lower.
 

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Hi and welcome to .org phil :)

I'm no specialist re sensors etc., only an idea just came to my mind - oxygen sensor ?

Have a read here (jump down to oxygen sensor, you can also find a 'how to test'
http://www.mgfcar.de/sensor/index.htm

Sorry if that's a double thought, dunno what iacv is :O

- spark plugs ok ?
- distributor cap and finger ok ?
 

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Discussion Starter · #10 ·
Hi and welcome to .org phil :)

I'm no specialist re sensors etc., only an idea just came to my mind - oxygen sensor ?

Have a read here (jump down to oxygen sensor, you can also find a 'how to test'
http://www.mgfcar.de/sensor/index.htm

Sorry if that's a double thought, dunno what iacv is :O

- spark plugs ok ?
- distributor cap and finger ok ?
Thats a real good page. Thanks
 

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How wierd. If you block the little hose to the iacv then it will run sweet!

weird - will try that then mate, the slow to come down the revs is why i damaged it, recorded tons of overrevs before finally giving in. My fault but highly annoying, your revs jusmp a little too then when you hit the clutch? Its like the throttle hangs on after my foot has left, then comes down slowly. The blip is obviously caused by the throtle still being on, but nothing to reign it in, giving that overrev before slowly dropping.

What are the long term effects of blocking the pipe? I feel it may be pipe related if this works..
 

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No long term damage but, .... well its just not right :dunno:. The idle air control valve is suposed to do just what it says on the tin. If it isn't then either the ECU is feeding it duff info for some reason or the main throttle isn't shutting properly. Stopping the IAC from working by starving it of air is just hiding the symptom imo.
 

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Discussion Starter · #13 ·
No long term damage but, .... well its just not right :dunno:. The idle air control valve is suposed to do just what it says on the tin. If it isn't then either the ECU is feeding it duff info for some reason or the main throttle isn't shutting properly. Stopping the IAC from working by starving it of air is just hiding the symptom imo.
Your absolutely right. I'm coming to the thinking that the engine must be sucking in some extra air from somewhere else.
 

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not tried getting one of those tiny little filters for over it? I'll have to get mine off and have a little lookie at where the pipe comes and goes.

To be honest I have whistles and sucks all over the place at the mo, i think i need a whole new exhaust system. It rattles a lot.
 
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