Cold Startup Issues

[jimmym86]

I've noticed a weird problem now that it is starting to get cold out...When I start the car, and it's fairly cold out (<40), it seems to run rough and slowly get up to the 1500 RPM cold idle and then smooth out. It usually takes around 5-10 seconds for the engine to smooth out, and up until that point it runs rough (almost seems like it's not getting enough gas or maybe too much). But once it gets close to the 1500 RPM mark, it's like God touches the car and it runs smooth. While this is occurring, I'm not seeing any smoke out the back. I've tried tapping the gas pedal after it starts to see if it helps, but it seems the only thing that helps is to let is sit for about 5-10 seconds. And if it warms up in the afternoon, it'll start just fine...So it seems to be related to the cold.

Any ideas?
Thanks-

[88mazdamx6tbogt]

this is just a problem on these engines as they get old. it is going into a cycle of warmup...the cold air being sucked in has an affect, but it is also the coolant, circulating around to all the sensors. if you search on here, you will see the name of the cycle, i cannot remember the exact term at the moment. it is a normal occurence, but if you are worried, check your temp sensor, coolant level/integrity, and thermostat. from what i remember, the dual-stage tstat on the turbo had something to do with this, making it work better at startup...instead of a generic tstat, which doesnt give the benefit of the initial stage on warm-up. the dual-stage is oem only, around 35 bucks. the car smooths out when the tstat opens, and the coolant goes around the engine sensors. you get the same surge if you are REALLY low on coolant.

[MazdaMiester]

double post. Geez IE sucks

[MazdaMiester]

Actually, this probably has less to do with a cooling system and more of a dirty idle air valve or problem with poor compression. The thermostat wouldnt be it because when the engine is cold, the temperature of the coolant is the same throughout the system. a thermostats job is to stay shut keeping the coolant in the engine seperate from the coolant in the radiator until the engine is at operating temp to where the coolant in the radiator will be used to cool the engine. Hes having this problem on cold start up, in the 5-10 seconds hes talking about the thermostat is just there to keep the coolant in the engine, a dual stage would do nothing for him because the engine would have to be at atleast 90-100 deg before the first stage opens(not sure the exact temp).

What happens is debris and dirt in the coolant pack around the spring in the air bypass valve. this causes the spring to hang up or take longer to open or shut. A bad valve will cause the idle to bounce between warm and cold start, or cause cold start to not exist. a dirty valve could cause a delay in the cold start procedure.

Another thing, with the age and milage on these cars the rings might need that 5-10 seconds to expand to build up enough compression...much like how diesels will misfire until they warm up. The car might not smoke because there is no telling how good or bad the rings are. People tend to judge bad rings by oil smoke, but we are talking about compression rings, not oil control. I would probably conduct a compression test... a warm compression test wouldnt tell you anything. A cold one would, but im not sure there are factory numbers for a cold test.

I'd try cleaning up the idle air control. It is located on the back side of the throttle body opposite the throttle cable. theres 4 phillip screws that you may need an impact driver because they're usually so hard to get out with a regular screw driver that you'll strip them. one electrical connector, 2 rubber lines. before you do this, buy a new gasket from mazda. its a few bucks, but they never come off in one piece and its about the most complex single ply gasket i've ever seen.

-Eric