i have a 97 mazda b2300 2.3l. my issue ive been having is when the temperature outside dips below 50F the engine doesnt run correctly. it seems to have a very slight misfire because of the fact that it shakes at high rpm (2-3k) and when sitting in a parking i could hear the miss. i dont know which cylinder it is so i havent tried doing any compression tests or anything of that sort. the engine does not burn any oil and fuel economy is perfect. and as the title suggests, the engine only does this in cold weather. if it is cool, warm, or scorching hot, the truck runs perfect and with all 112 horses. anyone have any ideas as to what is causing this? the only thing ive tried so far is running fuel injector cleaner but to no avail. the reason i havent tried anything else is because i live in florida so cold nights and mornings are rare, but when they happen i dont like to drive. any and all advice is appreciated.

 

not sure how many miles you have on the truck but I would clean the MAF and replace sparkplugs and sparkplug wires.

 

When it misses, is the engine wet with dew & does the CEL blink???
If so, have the computer scanned for trouble codes & post All code numbers here. Most autoparts stores will scan the computer at no cost if the CEL is lit, or your having problems.

If no CEL or codes, with the engine at cold idle, maybe try raising the hood at night & have a look around for arcing & sparking on the coil packs, plug wires & plugs at the trouble rpm.
If no joy, try a wet down test of each plug wire & coilpack, using a spray bottle of water & see if you can induce a miss, or see some arcing & sparking.

More thoughts for consideration, let us know what you find.

 

Humidity has no effect on the car. And like I said, the temp of the motor does not matter either, that's why I'm so confused. The MAF is clean. The engine has 220k miles, 150k of which are highway so don't jump to conclusions saying its someething like a head gasket or valve guides. I believe the miss is fuel mixture related because its not a complete miss but more like a light stutter. But thank you for all the suggestions, keep em coming.

 

Well with the mileage on this ride & the unknown maintenance/repair history, all kinds of things come to mind, from plugs, wires, coilpack breakdown, to worn timing belt, to O2 sensors & cat converter clogging, to sticking or burned valves & we could guess all day long & not do much good, so imo you may want to consider beginning with some meaningful diagnostic testing.

Hook up a scantool that'll read live PID's & have a look at long & short term fuel trim, engine temp sensor reading, MAF sensor output, O2 sensor switching range & speed & scan the computer for any set, or pending trouble codes. Maybe have the scantool do a cylinder balance test while your at it.

If you don't have, or can't borrow a scantool, hook up a vacuum gauge to a handy port & see what the vacuum gauge has to say.
If you've never used one, here is a link to a site with some moving gauge graphics & how to interpret what the gauge is displaying.
http://www.secondchancegararge.com/public/186.cfm

By then you should have some idea which system to move to the top of your suspect list.

Post your results here & we'll all offer up our next best guess on how to proceed.

More thoughts for pondering.

 

thanks for the advice paw paw. if it helps any the engine is in terrific shape for its miles. its had its oil changed every 3k miles its entire life and regular maintenance every 60k. and may i repeat that the truck runs PERFECT in cool, warm, and very hot weather. its only when its very cold outside that it does this random miss. something i forgot to mention before is that when im cruising at say 40mph at 2k rpms there is no shaking shuttering or anything of that sort. only when the engine is under load, like acceleration or climbing a hill, will it shake and stutter. sorry i didnt say this before because it seems like a critical variable. and yes it may seem like this could be caused my bad valves, head gasket, rounded cam lobes, low compression, etc. but lets pretend its non of those issues, that i can diagnose myself. lets say its an electrical issue not physical. what systems would fail or not work properly in very cold weather. im almost positive its a sensor issue or something like that but i have no knowledge of the computerized systems in this car. another thing i should have mentioned is that the truck used to have an idle issue after it sat for one year of its life, in that when started it would stall out unless you had your foot on the pedal. but after 5 minutes or so the computer would figure everything out and it would idle perfect. still has the same issue but i had a local mechanic look at it for me and he ghetto fixed it without saying what he did. now when it starts it will jump to high rpms before leveling out at perfect idle. this could also have something to with this problem im having. if you know what was done or have some kind of idea let me know so i can reverse it or fix the problem. please consider this last post than i shall not ask or any more of your time. thanks again.

 

A miss under load is a good clue & makes one want to suspect a spark problem.
Maybe excessive spark gap from worn plugs, a cracked internal or external plug insulator, or faulty plug wire, or cracked coilpack.
The wet down test at night is an easy test to do for ignition high voltage break down suspects.

The miss at idle could be caused by a number of things, from sticking valves, to low battery voltage causing a weak spark, to CCDF, or intake valve deposits preventing them from seating & sealing well, or maybe a sticking PCV valve messing up fuel trim, or maybe you have a faulty IAT sensor, the list goes on & on & you may have more than one problem, so thats why a scantool is so helpful, as it can monitor so many things at once, in real time.

The high rpm idle is usually caused by an acting out/sticking/dirty/worn IAC valve, so maybe your mech just cleaned it last time. Cleaning the IAC usually doesn't last, it didn't for mine, but was a good trouble shooting step for me.

 

one last thing, if you know, where is the idle air control valve at? would normally google but usually i dont find good results or it will bring me to a forum here haha.

 

The IAC is on the intake air tube, just in front of where it connects to the throttle body. There is one electrical connector to it & two fastners holding it on the intake air tube.
If your of a mind to try cleaning it, remove & clean it with a plastic safe cleaner like CRC CD electical parts cleaner, or MAF sensor spray cleaner.

Be sure to visit our "Tech Info" thread atop this forums thread listing page, for all sorts of helpful info.

If your of a mind to begin turning your own wrenches, a repair manual or CD is a good investment.