I didn't notice your location but what you likely felt was the car wants better gas. Give it some plus or Premium from a GOOD Brand - not fly by nite.Wow, this thread has been going on for a while. I guess it's my turn to join the party..
My 2004 Mazda 6S Auto (145K miles) has been having this hesitation problem for a few months now. It intermittently hesitates (stutters) at idle and it doesn't matter if cold/warm/hot, does it in gear, rpm drops and you can feel the "thump". I think it does it in park/neutral, but can't feel it nor does the rpm drop, I only noticed it through the sound of the exhaust. And it hestitates when under load, around 40mph. Problem started before I did anything to the car. Also, no CEL, no pending codes.
So far I have:
Replaced all 6 spark plugs with OEM Motorcraft (factory gapped to .054).
Replaced all 6 coils (denso).
Replaced Upper Intake Manifold gaskets (used Magnum's, and seemed a little too big, but i figured the rubber would compress)
Replaced PCV valve
Replaced Intake Hose (cracked in two places)
Checked PCV and other VAC hoses.
The problem persisted so I put in a bottle of Techron at fill up and made it all the way home, 20 miles without any hesitation, which seemed odd because I didn't think the techron would work that fast. And I didn't think much about it (thoughout the entire tank of gas/techron), until my next fill up (without Techron) and the hesitation returned. About 5 minutes after I pulled out of the gas station. Only thing I did to the car was change the AEM filter with the new red one (about 50 miles before fill up), other than that I open and close the gas cap.
I'm at a dead end here. I'm going to try cleaning the EGR valve next, not sure how it comes apart. Maybe perform a smoke test, but if it's a VAC leak, wouldn't the problem be more consistant? Also going to try another bottle of Techron. I may put the other AEM filter back on and it doesn't make much sense to me, but I guess I can try a new gas cap.
Any advice is greatly appreciated. Been following this site for years now and I've been able to fix most problems by just reading, but not this one.
That captures the bulk of it.Original Thread was Hesitation:
For all you folks who ** TEMPORARILY FIX ** the issue by installing new PLUGS, well i'd guess you're half way there! Now INSTALL NEW COILS and you're likely fix it!
Don't wait for or count on MIL/CEL to say the engine is misfiring P03XX. By the emission standards its aloud many misfires before it impacts EPA standards. By the time a single cylinder has enough continuous misfires to trigger a CEL, you'll be wishing you'd walked to work because it's really going to be running like crap by then! Not addressing misfires kills the CATs and takes the life out of your O2 sensors. . .
The tell tale signs of bad ignition coils: as the load increases it gets worse. i.e. in 4th gear, turn on the AC, Headlights, seat heaters, defrost, (add load). If the engine begins to stumble, its likely the ignition which is at fault.
COIL TESTING: OHMS and temperature wise the coils will test fine and EVERYONE PUTS them BACK! BAD IDEA! Its the dielectric break down voltage that you have NO MEANS of testing that is at fault. The spark is not getting to the plugs gap because its jumping to ground or back to the coils input. You can't detect this with an ohm meter! Replace the coils especially if you see cracks in the potting material as failure is imminent.
As for the throttle lag: On my V6 the engine is very sensitive to the quality of engine oil! Yes, pay attention to how it runs and shifts from idle and at low speeds right after an oil change. If I had to guess, the clearance in the VVT is very sensitive to the viscosity of the oil and the system pressure. Pay attention after the next oil change and see how it does. . .
Mine runs and drives much nicer on fresh oil!
I'd say it was worth the money for the dealer to run the diagnostics. Not sure what year your car is, but I paid $25 each for Denso coils from Rockauto.Hey Guys - Just got a call from the dlr - They say they are getting a reading that #3 coil is bad. The one under the intake; awesome.
So now i need to find some coils - NAPA has some Denso's for $77 each. I think i'll get them.
Funny thing - The dlr said the tech pulled a plug and saw carbon tracks or carbon build up on #3 . I said Really! He pulled the intake?! They said, oh wait, no he didn't pull it. I said well then why did he write that?
Anyways i hope this does the fix. I'll report back.
Dlr wanted $600. I think i can do it myself, i did the spark plugs once so i should be able to do this. I'll do all 3 plus those plugs, might as well.
Just because a transmission is maintained and has low miles doesn't mean it can't go bad, my Mercury cougar had 118,000 before I blew the differential out of it and it was maintained. My 2008 Mazda CX-7 sometimes likes to shift/stay in 3rd gear at 45 miles per hour, early warning? Maybe...Dude.... I have the SAME FREAKING problem!!!!!!! Unfortinatly I can't identify the source.... I doubt its the transmission (i have 80k on mine and have had 2 tranny flushes, one recently so the fluid is good) Supposudly its the Throttle body. However my problem didnt start until I got the plugs replaced. When im home over the xmas break I will try and clean the TB w/ TB cleaner. Its worth a shot....
There are a couple of TSB's regarding the throttle bodies... You might want to check in to that.I remember reading about throttle bodies going bad. It would cause bucking issues, and uncommanded changes in power. Just another possibility.
Did you have oil on your ignition coil boots? You May need new valve cover gaskets. It could cause misfire also.Having the same issue, runs smoothly until warmed up, then bucks and stutters while at load (i.e., particularly noticeable when going up a hill.)
I DID get a CEL, code ran as Cyl #2 misfire.
Replaced all spark plugs, and the coil for Cyl #2 . Issue still remains, although maybe not as bad as it was before.
Thoughts, suggestions? I'd hate to replace all the coils at this point, since they're $70 a pop, but it's doable. PCV valve needs to be replaced, which I discovered reading this thread. I'm running Gumout through it at this point, as the car is new to me and had sat for a while before I bought it.
Plugged fuel injector? Bad cat?
None that I could tell. VERY small amount of oil in one or two of the spark plug chambers, and a bit on the plug threads on the same, but we're talking eyedropper-type amounts. Still a potential issue?Did you have oil on your ignition coil boots? You May need new valve cover gaskets. It could cause misfire also.