Mazda 3 stutters/hesitates
 

Hi there,
I have MAzda 3i, 2.0 2008, manual transmission. 64K miles. Two weeks ago my car started to stutter/hesitate. Driving in 5th, around 3K RPMS, downshifting to 4th gear, the car starts to stutter/hestitate between 3700 and 400o RPMs. As soon as revs are above 4000 , stuttering/hesitation stops. Same stuttering/hesitation while on 3700 in 5th gear. Please note, when accelarating, I am passing 4200 in 3rd gear, all is fine, accelareting in 4th gear stutters around 4200, downshifting from 5th, stutters around 3700. I have replaced original spark plugs with BOSCH, now car is doing 32miles/gallon instead of 30 miles/gallon, stuttering is still there.
If anybody had same problem, pleaase let me know how you've fix it?
Thx

could be an issue with your maf being dirty, ive had problems with mine twice even before i put my intake on, it could be also the ****ty bosch plugs, me and lot of my friends have nothing with problems with bosch plugs. You could other problems though, electrial issues are a pita with these cars, id just take it to a trusted shop.

Last Thursday the Check Engine light came on. Today brought the car to the shop, Gemini Goodyear, the diagnostics show the Air-Fuel Ratio sensor was malfunctioning. So, diagnostics, new sensor ($450), labor and fuel lines/canals cleaning ( Gemini does it with the BG products), $800 later I got my car back. Will see in next few days if that fixed the problem. Also, the shop maager repeated Trackers advise, to take the Bosch plugs off and replace them with NKG. Any idea/experience why the Bosch shouldn't work? I came from Europe, wher the Bosch is the recognized quality. I had very good experience with Bosch in Europe. And, european car or Japanese, at least that's my opinion, spark plug is doing the same work. No mater the car origin. As engine basics should be the same. Spark plugs I have used are Bosch Platinum +2, Platinum and Yttrium +2 ground electrodes. With those plugs my gas milage went from 30 to 32. Just looking for good reason to replace new plugs.
Will post new thread after I'll teast the car, most likely next week, when I am back to the interstate.

A few points:

• Fuel system cleanings are a scam, rarely (if ever work), and are a huge profit item for service centers.
• If the OEM plugs are a specific NGK plug then they're the ones you should use. Why? While other plug makers might make a plug that has similar firing latency and heat dissipation characteristics, engines these days are designed to be very closely matched with their spark plugs, and even the slightest change in the heat range can negatively affect engine and emissions performance.
• It is physically impossible for a simple change in spark plugs to alter your fuel economy one wit, much less an increase of two miles per gallon. I've heard and read countless anecdotal claims of spark plugs improving fuel economy; however, I've never once seen a single shred of scientific evidence that supports said claims. On the other hand, there is a huge body of scientific evidence that shows some combustion chamber designs benefit from the addition of a second spark plug either to form two flame fronts or, if the fire in series, to help ignite small end pockets of gas before they can detonate.

Long story short, refuse all future fuel system maintenance offers, and go back to the OEM plugs.