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Topic: rough running when cold (Read 509 times) |
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tintin
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rough running when cold
« on: May 20th, 2007, 9:13am » |
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ok, not a bad one, since i replaced ecu and ccm, car is running great BUT .....
when it first starts up, the engine runs very lumpy and shakes when idling at lights/juntions etc. as the car warms up, it lessens until when warm it idles perfectly at 800rpm.
another symptom, car runs dead centre on the temperature guage, but if it sits in traffic a long time, temp goes up slightly, but only just above the centre. stop the car, then get back in 5 mins later and temp is up to 3/4, and wont come back down (except with 30mins motorway driving). its never overheated.... both fans come on as they should. its done this since the new rad was put in, i dont think there is any coolant in the mix.
scan done, no error codes (although one postcat sensor looks a bit sluggish), MAF is clean, IACV clean, etc
any thoughts? as i said, its not life-threatening, but i am a perfectionist (when my wallet allows me  )
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'95 Cosworth Ultima
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Spannerdemon
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Re: rough running when cold
« Reply #1 on: May 20th, 2007, 4:02pm » |
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When you replaced the ECU, did you also disconnect the battery for a couple of minutes? If not, it would be a good idea to do so.
You need to do this so that your new/replacement ECU can 'learn' your car's settings. Everything from fuel flow, to idle, to ignition timing etc.
When you do this, the car WILL run rough for a few miles, and then settle down once it has taken in the information to enable smooth and economical running 
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tintin
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Re: rough running when cold
« Reply #2 on: May 20th, 2007, 5:27pm » |
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i assumed that unplugging the ecu was equivalent of a battery reset for it 
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'95 Cosworth Ultima
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Dave2302
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2006 Mercedes S55 AMG, Retired Barefoot Waterskier
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Re: rough running when cold
« Reply #3 on: May 21st, 2007, 4:30pm » |
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I would assume the same
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Dave "The 'ol Bear" ex Footer !
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tintin
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Re: rough running when cold
« Reply #4 on: May 21st, 2007, 7:25pm » |
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not sure if this is one problem or two another symptom is has always had is that the revs sometimes dip at idle (in gear at lights), then recover to a smooth idle.
im wondering about the temp senders, but not sure how they would tie in with the symptoms...... i know if it thinks its very very cold, it would overfuel.....
other thought was TPS, but reading on the scan was fine (car was warm and behaving), dont think it is temp sensitive.
last thought was air lock somewhere
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Spannerdemon
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Re: rough running when cold
« Reply #5 on: May 21st, 2007, 7:43pm » |
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I personally wouldn't EVER connect up a new ECU to a live socket, but understand what you're saying. I always disconnect the battery when working on any car electrics which is recommended procedure when working on cars.
I've seen too many 'fry ups' with electrics to take chances with expensive components.
Earlier this year my own TPS gave up, even though it was reading OK, so I wouldn't discount it. it may well have an intermittant problem.
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Dave2302
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2006 Mercedes S55 AMG, Retired Barefoot Waterskier
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Re: rough running when cold
« Reply #6 on: May 21st, 2007, 8:25pm » |
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need to check live data to look at Temp sensors and tps while on a drive from cold..... you'll be looking for smooth transitions all the time
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Dave "The 'ol Bear" ex Footer !
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