Lumpy Idle...normal!

[steve_rt]

Ive had this for a while now, and i just put it down to an over-efficient ECU tryin to save me as much fuel as poss by gettin the mixture as lean as possible. But having sat in other cars (inc. a Mk1 Ph3 clio ) whcih idle smooth, im wondering what may be at fault?

It will idle slightly rough from the moment the key is turned, when its hot and youre sitting in traffic, you can feel the engine do a mini jolt when the revs drop by 200 or so, then pull back up. Its not worse when hot, its there all the time.

is this normal? what may be gone?

 

[BRUN]

could be loads of things, most extreme would be a water damaged ECU.....could also be throttle potentiometer........idle speed motor (£60 very easy to replace yourself)......an loads of other tings.........could be as simple as a dodgy wire mate

 

[steve_rt]

if i drop it into reno and they run an ecu diag will that highlight the problem?

can you test any of these things you mention brun?

 

[BRUN]

it could do yea, make sure you specifiy you just want the diagnostic........or they might start doin other things.....

 

[steve_rt]

lol, ive still got a whlole side of my car banged in, i can just imagine: "oh sir, we fixed your snapped wire, and also took trhe liberty of replacing the door and rear quarter panel...now if we could just settle the bill...."

 

[timrud]

Mine does this (Mk1 Ph3) when I start it up its fine, but if I drive somewhere, then say stop at some traffic lights, it is a lumpy idle, but if I give it a little squirt on the accelerator then let it come back to idle its fine. Any ideas what that could be?

Tim

 

[Scott Wood]

Mine went down last week for a diagnostic check, when you first start the car up, it runs lumpy, as soon as you start raggin it, it would idle high, dont know if yours does this as well, but the check came back saying that i have a faulty motion sensor! gotta til i get paid til i can get it!!!

 

[steve_rt]

doesnt sound much like mine - gonna change the leads / cap / arm and see what happens, but from what ive searched on here it could be a idle control valve sticking, throttle potentiometer (is that a throttle position sensor?). anything else?

cheers guys

 

[BenR]

most likely to be the ICV, or the readings from the potentiometer affecting the ICV.

 

[steve_rt]

cheers as ever ben, ill look at it later!

 

[Chris_H]

Bet you a white magnum the valve clearences are to pot.

 

[BenR]

dont like white, can i have a mint and chocolate lolly instead?

But try get them to check the clearances.

 

[steve_rt]

done them when i bought the car 9mths ago, would they go out that quick?

the ICV (called an idle speed control motor in haynes bible, that what you call it?), how do i test it?cant be anythin on ignition sys like leads, dizzy as it is only occasional, as in it will run fine most of the time but occasioally blips, not a misfire more a skipping?!!!

ill give you as many sweets as you want, tho you might have to share if you both solve it together

 

[BenR]

take the air filter assembly off, and just watch the ICV. its obvious if its messing you about. just pull the throttle cable then watch teh motor slow the revs down, if its jerkin you about then get it on an XR25 at renault.

Could also be a bust lambda messing you about if its not providing the right 0.5v to the ecu, it could be searching.

 

[Chris_H]

on the energies I find when you adjust them they go out of adjusment every few months or so. My theory is the hardening, they wont have been touched so worn a straight line, then you move it it wears an x which turns. I have rockers that back this up.

Anyway the idle stepper motor, if the idle stays constant then its more tyhan likely fine.

These cars do as a charactersitic even when everythign else is bang on have a wee jolt after a min or so of idling.

Dodgy clearences, dirty TBs and manky breathers do not help much either.

 

[BenR]

Sorted then, check everything!

 

[steve_rt]

chris, its more than a wee jolt every min or so - havent had the time to get under the bonnet, but just went round the back to listen to the exhaust, it loses its pressure about every 3-5 secs, sometimes v slight sometimes momentarity completely - this still tie in with valves? TBs - would fuel additive clean these, as it had it a couple of thou miles ago.

 

[BenR]

no fuel additive will fix it. take your rockers arms off and check the wear pattern like chris says.

Then set them again.

 

[steve_rt]

ok mate, thanks for your help.

 

[Dazz]

steve_rt, did this actually solve the problem as ive had a lumpy idle on mine since ive had it.
Thanks

Dazz

 

[Flying Scotsman]

When i had my 1.4RT it would never idle smoothly when hot, the gearstick always wobbling a bit. The problem never seemed to be consistent ... some days it would idle sweet as a nut. I put it down to ECO engine management settings too. Having said that all my 1.6s, 99, 00, 01, 02 and current 03 since then tend to do the same thing when hot. Never had a problem with the 172 although it tends to hunt a bit due to rich running when cold but always idles dead smooth when hot.

 

[maff]

I get lumpy idle and i put it down to the stereo. If i disconect the amps for a day then the car runs fine! and yes it is all wired in correctly! lol, im goin yo try one of those optima yellow top batteries when i can afford it.