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post #1 of 12 (permalink) Old May 13th, 2014, 04:56 PM Thread Starter
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rough idle on cold start up few seconds

I have an 03 R53 Cooper S JCW and every morning when i start up the car she idles a bit roughly as in the revs very slightly increase and decrease. The unsteady idle goes away after about 10 or 15 seconds after. My mechanic at BMW tells me it is because my car is decatted and the resonator removed so the oxygen sensor reads wrongly. Is this true? I can upload a video if anyone needs
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post #2 of 12 (permalink) Old May 13th, 2014, 05:03 PM
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Hi

This is possible but it could be other things
has your car been remapped at all or you running the standard mapping ?

Are you running any other mods ie intakes, pulleys ?
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post #3 of 12 (permalink) Old May 13th, 2014, 05:14 PM Thread Starter
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Nope have the standard map, note i have the 200hp kit not the 210. Have a K&N cone air filter, otherwise everything stock. Car never used to do this when decatted, most recent change is the resonator delete but even then it still started up fine.

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Originally Posted by marque View Post
Hi

This is possible but it could be other things
has your car been remapped at all or you running the standard mapping ?

Are you running any other mods ie intakes, pulleys ?
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post #4 of 12 (permalink) Old May 13th, 2014, 05:42 PM
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Nope have the standard map, note i have the 200hp kit not the 210. Have a K&N cone air filter, otherwise everything stock. Car never used to do this when decatted, most recent change is the resonator delete but even then it still started up fine.

Ok cool
well I don't know if you are aware of this but by removing the cat you are loosing power :-(, the mini need the cat in standard trim. Basically you are telling the ECM porkies and you will mess up your AF ratios which means you will kill your engine. The standard manifold and cat will handle 230 plus hp.

This is way you will find most of the guys who change manifold to janspeed, JC and OBX will splice the standard mini cat

If you want to run with out the cat you will need the car remapped by someone like 1320 but they will advise you most portably to run the cat
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post #5 of 12 (permalink) Old May 13th, 2014, 05:51 PM Thread Starter
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Ok cool
well I don't know if you are aware of this but by removing the cat you are loosing power :-(, the mini need the cat in standard trim. Basically you are telling the ECM porkies and you will mess up your AF ratios which means you will kill your engine. The standard manifold and cat will handle 230 plus hp.

This is way you will find most of the guys who change manifold to janspeed, JC and OBX will splice the standard mini cat

If you want to run with out the cat you will need the car remapped by someone like 1320 but they will advise you most portably to run the cat

Wow ok well that makes sense, the car doesn't quite perform anymore anyway. And im purchasing a GP next week which is also decatted....**** i guess ill have to recat then.

Thanks for the help most intriguing I shall certainly be changing my thoughts on decatting minis now.
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post #6 of 12 (permalink) Old May 13th, 2014, 06:03 PM Thread Starter
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Oh sorry one more question, after doing some research on loss of power with decatting i notice people mainly do it for the sound, now i am a huge fan of the sound when i stamp on it so would a resonator delete have any effect on the peformance? Should i just get a janspeed manifold?

I am down in Cape Town South Africa so acquiring tuners with mini knowledge and ordering parts is quite hard.


Many thanks!
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post #7 of 12 (permalink) Old May 13th, 2014, 06:09 PM
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Wow ok well that makes sense, the car doesn't quite perform anymore anyway. And im purchasing a GP next week which is also decatted....**** i guess ill have to recat then.

Thanks for the help most intriguing I shall certainly be changing my thoughts on decatting minis now.
If your buying the GP find out if it's been mapped and who buy then you can call them and find out if it was mapped with or with out the cat.

Depending on how it's been decatted it may have something like a janspeed manifold with a decat pipe installed. Which is an easy fix to put the cat back in

'The Tom-Cat' For Janspeed Manifolds. MINI - Servicing - Repairs - Tuning - Parts - Spares
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post #8 of 12 (permalink) Old May 13th, 2014, 06:19 PM Thread Starter
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As far as i know its stock apart from being decatted, how its been decatted though i dont know, i shall find out.

As for sound/power gains what is the best route? I read a forum on mini torque that ultimately says a manifold upgrade with/without a decat is useless for power gains unless properly tuned with a map. Naturally other users say they significantly noticed an increase in performance when upgrading manifold and decatting/sportscat also they claim dyno figures?

here is the forum


minitorque.com/forum/f24/decat-power-loss-how-much-40547


ok i see the tom cat on 1320's site, so cat is definitely the way to go, i shall definitely dyno the car once purchased and then go from there with modding


Once again thanks as you are much more clued up than me
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post #9 of 12 (permalink) Old May 13th, 2014, 06:50 PM
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No problem I was there once

The big problem is with decatting with out it being remapped or set up properly is the damage to the engine not so much the power

Personally I went for an OBX manifold it's 4-2-1 which I find gave me more mid range power it's a good price and not bad quality. And made a cat for it out of my old standard manifold. Basically a tom cat a local exhaust shop can help you out there.
The other option is a janspeed with a tom cat. I looked at miltec but there were problems with the cats falling apart but it might have changed by now.
If you could get hold of a JCM manifold but there like rocking horse pooo they are good

You could by a standard exhaust from a breakers for £60 to £100 and cut the cat off to use


If you want parts I use rich at orranje can really recommend him

Orranje - New MINI Performance & Styling Products
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post #10 of 12 (permalink) Old May 13th, 2014, 08:34 PM Thread Starter
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Ok i see, ive seen a lot of janspeed manifolds and they sound pretty nice and seem to have good reviews so i shall look it up there.

First let me just get it over and sound like an idiot, i have a basic concept of a cat and know it changes the toxic pollutants etc but now it is the bulge just after my headers right? it looks like kind of weaved and stuff. Is decatted that cut off? or just the bits knocked out that convert the toxins. I still have the cat (bulge thing basically) but the guy at BMW said its not fully decatted so with the bits knocked out will it still confuse the ECU?

Once i've understood that then i think i'll want to get a Janspeed manifold for the gp and keep the exhaust as it is. Will i need a tune with the new manifold? Another thing if i get parts from orranje do they ship to south africa because that seems to be the biggest problem here, the tuning community isnt big enough
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post #11 of 12 (permalink) Old May 13th, 2014, 09:45 PM
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Hi ya

Yer cats funny old things when they decided to go away from leaded to unleaded they found that they were putting out some bad chemicals worse than leaded.
So they shoved a cat on there to take out the toxic chemicals and hydrocarbons.

You have a pre cat which is there for cold temps ie from -20 to 0 deg c for instance and then the main cat for the car during normal running. The big problem is the 02 sensors monitor the emissions and sends a signal yo the ECM telling it wether it need more fuel less full to be with in a determined threshold at low rpm, this is the simple version it's more in depth but you get the basic point

I have attached a picture from the head flange the first bulge is the pre cat the woven mesh part is the flexible joint and the next bit it looks like a silencer it the main cat


Hope this helps there is no such thing as a silly question
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post #12 of 12 (permalink) Old May 14th, 2014, 10:51 PM Thread Starter
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Ok definitely decatted then, i have the woven mesh but other than that there are no bulges, i shall be checking out my gp next week to see how that exhaust is looking
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