When I stop at a stoplight or whatever, my car has this weird idle. It's not really an idle as much as the car sounds like it's gargling and trying to shut off. It doesn't do it everyday, more on cold days. If it is warm outside it doesn't do it. It has a rythym to it and can sometimes take a few seconds or a minute before it starts doing it. The idle is normal then it just starts to shake a little in this rythmic pattern. Only does it in drive and reverse. The moment I put it in N or P it stops and once I lift off of the brake it stops. Only when I have my foot on the brake, completely stopped, and in drive or reverse. Like I said doesn't do it all the time though. Please help.

The dealership said that I had a broken engine mount, but I'm not sure that that is causing this problem since it mostly does it during colder weather. Not during the summer or on warm days about 60.

2004 over 90000 miles. I know I need new spark plugs about 10000 miles from now. New battery, just replaced a month ago.

What do you guys think? Please help before I replace this engine mount and then it's not the problem.

 

Engine mount, I really doubt it. I had a Honda with bad mounts and it didn't have these kind of symptoms. When I shifted there was a knock sound and that's it. Friend of mine also had bad mounts and his would make a single knock sound when shifting.

 

What year is your 3? I just had the same thing happen with mine. I have a 2004. The recommendation was to clean the throttle body and/or replace the thermostat. I replaced the thermostat, but still got the same result as you did. Like you, I noticed that it only happened whenever the car was in gear.

Kinda puzzled too....

 

Try cleaning idle air control valve. I have a millenia and it does the same thing.

 

There's a thorough troubleshooting procedure in Mazda's workshop manual for this symptom. I highly recommend you check the price at your dealer on (and acquire if you can) the workshop manual for your 2004 Mazda 3. While they're geared towards Mazda trained techs with Mazda's equipment in mind on some issues, it can still be a VERY valuable resource to you, and may pay for itself after awhile.

Part of the troubleshooting for that issue requires you to see if there are any DTC's (diagnostic trouble codes) stored in the PCM (powertrain control module), but you might be able to pull those if you visit an autozone or oreilly's and get them to scan it for you. If you do, just write the codes down--DON'T listen to the parts store guy if he tries to tell you what he thinks the problem is. Most of the time they don't know what the hell they're talking about.