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Did you see oil on your coil boots? I have a valve cover gasket leak too with oil on my #1 plug. I used to feel a small amount of hesitation while accelerating uphill in 3rd gear.

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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)
Cleaned MAF
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.
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.

Also, you had the intake off, so was the ECM reset?

PS - I'm all for Techron 4x a year. But as you said, its not fast acting other than changing the burn rate. I run Plus and get better MPG which is enough to offset the cost of the fuel cause I go further per tank AND it reduces hesitation.
 

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Also - another factor is the quality and condition of the oil. THE VVT WANTS GOOD OIL PRESSURE to operate effectively.

A dirty MAF, a vacuum leak, old oil, crappy gas, all these things combines lead to a shitty running car!

Look for a vacuum leak too!
 

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There was a tiny bit of oil in two of the spark plug "slots", kinda pooled at the bottom. And one coil boot had a bit of dried oil on it.

I didn't reset the ECM, I've never reset the ECM on an air filter change. I did reset it during the spark plug/coil change. My last two fill up, I used the same gas, from the same gas station in Springfield VA, with and without Techron. Both 87 octane. I'm trying my best to "burn" through this tank asap. Thanks for the theory/suggestion. I'm happy to try it, before I put anymore money into the car.

Update:

It looks like my hesitation issue is gone. I had about an 1/8 of a tank left and decided to fill up. I used a different gas station this time (Shell this time, instead of Exxon from my last two fill ups). I filled up with 87 octane and another bottle of Techron. I've been through two driving cycles, about 30 miles, and have not noticed any hesitation at idle nor cruising around 40mph. I'm going to fill up with Shell gas again next time and hopefully I can move onto my next problem (oil leak and front suspension noise). Thanks for your help everyone.

Another update:

Looks like I spoke too soon. Hesitation has returned with same tank of gas... but it threw a CEL this time. Cyl 2 misfire. I've never been so excited to see a CEL. I just moved both the spark plug and coil to another cylinder, even though they are both brand new. Hopefully, I'll get another CEL soon.

Fixed:

Turned out to be a bad spark plug (a brand new one out of the box). I suspect it was defective out of the factory and the gap was the same as the other plugs. I never got another CEL, but I just decided to spend the $5 and try replacing the spark plug. I've driven almost 1000 miles on the "new" spark plug and not a single hesitation.
 

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Hi Guys. A lot of great info here but looking for some resolution.

I am experiencing the exact same hesitation / stuttering that the original poster and several others described.

Took it to Joe mechanic down the street and they couldn't diagnose it. No CEL and no stored data history of 'missing' on any cylinders. They also say they couldn't recreate the problem, but it did it on the way home from them.

It's at the dealer today for a $120 diagnosis.

After 29 pages of thread here, it's hard to tell what the solution was to this problem?

Can someone please tell me what the consensus is/was?

Thanks in advance!!
 

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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!
That captures the bulk of it.

  • Plugs at proper gap (they fit many applications and require adjustment).
  • New Coil Packs. And yes, a RANDOM DEFECT can be dealt with a NEW COP or PLUG! It happens!
  • CLEAN the MAF
  • Correct ALL vacuum leaks! That means take stuff apart and touch it! Looking at the cars antenna from 25' away is about the same as lifting the hood and saying you checked for leaks. Its of no value until you get your hands dirty.
  • Change the oil (unless your fault is a misfire), this helps response of the VVT.
  • Good Gas of 89 octane or better (advances ignition = runs better!)
  • Open it up in 3rd gear on long steep hill and blow the carbon out of it monthly!
 

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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.
 

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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.
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.
 

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Yes, def money well spent to know exactly what it is. Correction; the dealer wanted $770 to do all three coils on the back bank. I bought the OE coils from napa at $77 each (yikes!) and will attempt to do myself.
 

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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....
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...

I remember reading about throttle bodies going bad. It would cause bucking issues, and uncommanded changes in power. Just another possibility.
There are a couple of TSB's regarding the throttle bodies... You might want to check in to that.
 

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2004 V6 bucks when it rains

Problem started in March when the car started bucking when it rained. Since then I have had over $3,000 worth of repairs including all coils, PVC, O2, plugs and a leaking hose under manifold. CEL kept on coming back on with numerous codes. Since we have had not much rain this summer, no problems. Yesterday the CEL came on and today it rained and car started bucking again and flashing CEL. Any suggestions??
 

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Same issue

I'm having the same issue and have used a bottle of heat in the tank of fuel to try to clean the fuel injectors and changed spark plugs and am waiting for the new coils to arrive to change those...hoping that will do the trick as many posters have stated that this has helped them on the issue, but I also see many have continued having issues even after coil replacement. Also cleaned the throttle body. I purchased OBD II code reading device(cant remember what the actual name of it is) but it wont work when connected to the OBD port on the car...took it to autozone and their code reader wont work with it either....anyone else having a problem getting the OBD reader to work on their Mazda 6? I hate having to go to the dealer as they charge $100.00 just to run the check? Can't understand why my unit works on all my other vehicles but not on my mazda? The autozone guy said that sometimes the purchased OBD units wont work if their is a single burnt fuse anywhere on the car so I guess I will be checking all my fuses to see if I have one that is preventing the OBD unit from working on my mazda. If the new coils correct the problem, I'll post results.
 

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To throw another variable, or two, in the mix...my hesitation didn't go away till I switched to MSDS headers and put in a new fuel pump. I'm leaning more toward the pump that did the trick. Go with a good Mazda pump, the "advanced auto" pump would not read correctly on the gas gauge, but the hesitation was gone...or barely noticeable.

If you replace your pump, get the tool from a shop or amazon. I split my finger on the metal surround trying to do it with a screwdriver and hammer...then manually turning it without gloves.
 

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hesitation

Was having the same hesitation problem that everyone talks about with the Mazda 6's. I have a 2005 6s. If you're having this issue theres a 90% chance that its one of the coils.

I replaced all 6 coils and plugs and while you have the intake manifold off you might as well replace the upper intake manifold gaskets so you don't have to ever take it apart again. I also replaced the MAF sensor and inspected the intake hose as well as cleaned out the throttle body. Problem solved, runs like new. I'm pretty much a novice and never had it apart like that before and it took me about 3 hours total to do everything. The only issue I ran into was I broke that stupid "T" for the throttle body coolant line which I did the basic throttle body bypass mod.

Hope this helps anyone who runs into this problem, it haunted me for a while. I was getting no check engine light or CEL codes either.
 

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than n, it is an Ignition coil like stated that causes a hesitation in these cars. And sometimes depending on the year model, it'd be the Throttle body.

Usually an easy fix. but can sometime be a lil difficult to diagnose if the person diagnosing isnt familiar.
 

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Not the coil, maybe?

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?
 

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One issue I came across was 5 out of the 6 connectors going into the coils had the locking clasp broken or I broke off when I went to plug them back in. I had to run zip tys from the connector around the top of the coil. It could be the connectors sliding out if the connectors aren't locking in, or it could be a problem with the wiring harness itself. I've also heard of people having trouble with cheap coils going bad very quickly so I'd advise using a better quality coil under the intake manifold.

Like I said I'm a novice and in no way am a mechanic, but I was having the exact same bucking under a load, at times horrible and it's completely gone now. Good Luck.
 

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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?
Did you have oil on your ignition coil boots? You May need new valve cover gaskets. It could cause misfire also.
 

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Did you have oil on your ignition coil boots? You May need new valve cover gaskets. It could cause misfire also.
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?

Edit: Forgot to mention, all of the plugs looked good. Standard wear and discoloration, no oil residue, and no oil on the insulator or above.
 
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