When car is first started, it runs very rough (as though not firing on all 4 cylinders) then after a minute it runs fine...spark plugs look clean...
This could be caused from bad rings as well. Your engine could have a cylinder with bad piston rings that are not sealing until the engine gets warmed up. Do a compression check with the engine cold and then when it warms up. Atleast it will help you narrow it down on internal problems.
Just to make sure we're clear.. only running on three-cylinders would make it run really really rough, to where it will barely stay running and if you put it in gear it will probably die or come close to it. considering it runs normal shortly after warming up a little, this is probably not the case..
couple questions first though...
has this been a chronic problem all winter?
was it colder than normal when you noticed it
if either of these are the case, and it is running rough, but quiet as rough as i explained above, it may just be the cold..
O2 sensors (in the exhaust) don't work until they heat up to operating temp (several hundred degrees) and until this point, the computer metes fuel according to a set map that is set for a normal temp range.. when really cold some engines will run rough because they are not getting enough fuel (the colder an engine is, the more fuel it needs to star/run until it warms up, and the O2 sensors tell the computer how to properly meter the fuel according to a 14.6:1 (air:fuel) ratio
also, what rpms does it run "rough" at? and normally?
..finally, when it is warm, and you shut it off and start it back up a short time later (while it is still a bit warm) does it run rough as well?
so, if it starts/runs fine while warm this could be the only "problem" which is not really a problem, rather just a minor inconvenience..
if it starts as rough when warm, as when it is cold.. this probably has little to do with the problem.. i'll look for your answer's to see if we need to diagnose a different problem
Seem like you got the same problem as my scion xa, check the fuel pressure regulater. bad regulater some time smell like leak gas. auto zone might cause you about $80.00.
My 1996 chevy s10 runs rough when first stared. after 15 seconds smooths out
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It has run fine, until recently...it does'nt seem to want to die, just the first few minutes when started it runs rougher than it did ( I just bought the car) spark plugs look ok,
It occurs when the car is first stated (warm up mode) so I'm thinkin at 1500 rpm, then you can feel it break through what ever restriction that goin on, and run smoothly,
When you start car in the morning it Idles around 1500 thats when I notice, then after it warms up, it smooths out,(wasnt doin this a couple days ago) also you asked while car is still warm, does it do this? yes...
i have the same prob in my 89 gmc 1500, it started when i put a thermostat in
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