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Discussion Starter #1
I just purchased 2014 Mazda 3 2.5L w 200,000km (mostly hwy) When the car is idling I can feel slight hiccup. I just replaced the spark plugs which is scheduled maintenance @ 110,000km however the issue is still there. I know with direct injection the intake valves should be cleaned every 10-15miles.. not sure if they were every cleaned never scoped the runners yet.

1. Anything else to consider?
2. Walnut shell blasting vs intake cleaner? (Which method)
 

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There are many causes of a rough idle. For example, one could be an intake leak somewhere.

Who told you that the valves need to be cleaned regularly? Not with these engines. If you really want to, walnut blast is the way to go but it's unlikely to make any difference. There are many posts about this on these forums including the one I wrote up a while back. I did the walnut blast and it was a waste of my time.

First thing we need to know is if there are any ECU error codes. We need to see if your engine is actually misfiring at idle.
 

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I just purchased 2014 Mazda 3 2.5L w 200,000km (mostly hwy) When the car is idling I can feel slight hiccup. I just replaced the spark plugs which is scheduled maintenance @ 110,000km however the issue is still there. I know with direct injection the intake valves should be cleaned every 10-15miles.. not sure if they were every cleaned never scoped the runners yet.

1. Anything else to consider?
2. Walnut shell blasting vs intake cleaner? (Which method)
Blast it.

Sent from my SM-G970F using Tapatalk
 

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Did that hiccup , was it on a start? would show as a cold start misfire code?
MAF Sensor .... but that should show a code.
Fuel delivery issues ... dirty fuel filter.
Intake solenoids ... usually make a ticking noise
Injectors dirty ... I'll recommend Liqui Moly fuel system cleaner. (after 260K kms) i changed the injectors (went with Bosch 62400)
Sparks Plugs you changed, were they the mazda oem (NGK iridium)
Ignition coils ... perhaps should also show a code.
 

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Discussion Starter #6
Did that hiccup , was it on a start? would show as a cold start misfire code?
MAF Sensor .... but that should show a code.
Fuel delivery issues ... dirty fuel filter.
Intake solenoids ... usually make a ticking noise
Injectors dirty ... I'll recommend Liqui Moly fuel system cleaner. (after 260K kms) i changed the injectors (went with Bosch 62400)
Sparks Plugs you changed, were they the mazda oem (NGK iridium)
Ignition coils ... perhaps should also show a code.
Idle has small sputter doesn’t feel smooth. I replaced the plugs with NGK Iridiums and also adding Lucas fuel system cleaner.. No codes yet?

Whats your next recommendation?
 

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You mean the wrench in a can didn't work?? Big surprise.

I'd suspect a vacuum leak somewhere. Small enough that it may not be setting off a code. The ECU codes are not the be all and end all.

Testing for a leak is actually not that hard. First step is check all the vacuum lines for any cracks or damage, replace as needed. For testing, best and safest way is to use argon gas if you have access to it. Know any welders? Argon gas will temporarily seal a leak and cause your idle to smooth out.

The trashy way is propane gas. Obviously propane is flammable so be careful. Only do this outside and make sure you don't have any spark. If you have a garage, it's not a bad idea to look under the hood in the dark. See if you can see any arcs. A damaged wire grounding out could also cause your idle problem.

Small propane torch and don't light it. Spray some gas around intake parts right up to where the manifold bolts to the head. Remember, you're looking for a broken gasket too. If you find a leak, the propane will cause your idle to increase. Since the engine has to pull the gas in, there is a delay with this test. Same with the argon. Go slow. let everything air out well when you're done. Closing the hood will hold the gas in.

WD-40 will also work but not as well since liquid is much thicker than a gas.

Fuel is a possibility although unlikely. Normally you'd see a fueling problem under heavy engine load rather than idle. Regulator not providing enough pressure at the low end is possible even if unlikely. Only way to test that is to get a pressure gauge on it. Pump is out, if it can handle high load it can handle idle. Same goes for the inlet filter.
 

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I forgot to mention. ... a dirty air filter
 

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No. Not a dirty air filter. Dirty filter means less airflow into engine. Sensors are very happy to adjust fuel to suit. The only result of a dirty filter is reduced power until it's flowing practically nothing.
Thanks
I figured so much.

If it is of any insight. I've been told by OV Tune that coldstart parameters on our ecu "Mazdaedit/Epifan software" fuel/air ratio is very rich and on my set up cause a CEL misfire and does feel like a hiccup. Now is @Zoom_2014 hiccup creating a CEL?
 
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That's actually a good point. Sometimes codes don't keep the CEL on but will be logged. Emissions system is a possibility, but with no code to back it up it's unlikely. Coolant temp sensor could be slightly out of spec. Might not be enough to throw a code.

Thing is a misfire should be logged in the ECU. Sure it doesn't always work as it should, but trying to figure out if there might be another cause.

Two thoughts. Check for an exhaust leak. A small one may affect the O2 sensors without throwing a code. It SHOULD throw a code, but I feel like we're getting into one of those unusual ones here. should be able to find it under the car by looking for the telltale soot. It'll be between engine and cat.

Another thought is a failing ignition coil. I'd expect this to present misfire under load, but it's easy to check. Use a multimeter to check coil resistance. Values are in the service manual of course.

On that line of thought, same could be for the injectors. They could be clean enough but if coil is on its way out it might not have the force to open the valve enough.

The dirty valve thing is very unlikely so I'd leave that as the last thing in line. At idle the air flow demand is so low that even valves that are a total mess shouldn't matter. Reduced power, especially under load, and reduced fuel economy would point to valves.
 

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That's actually a good point. Sometimes codes don't keep the CEL on but will be logged. Emissions system is a possibility, but with no code to back it up it's unlikely. Coolant temp sensor could be slightly out of spec. Might not be enough to throw a code.

Thing is a misfire should be logged in the ECU. Sure it doesn't always work as it should, but trying to figure out if there might be another cause.

Two thoughts. Check for an exhaust leak. A small one may affect the O2 sensors without throwing a code. It SHOULD throw a code, but I feel like we're getting into one of those unusual ones here. should be able to find it under the car by looking for the telltale soot. It'll be between engine and cat.

Another thought is a failing ignition coil. I'd expect this to present misfire under load, but it's easy to check. Use a multimeter to check coil resistance. Values are in the service manual of course.

On that line of thought, same could be for the injectors. They could be clean enough but if coil is on its way out it might not have the force to open the valve enough.

The dirty valve thing is very unlikely so I'd leave that as the last thing in line. At idle the air flow demand is so low that even valves that are a total mess shouldn't matter. Reduced power, especially under load, and reduced fuel economy would point to valves.
Again ..i totally agree on those borderline possible maybe setting off a code but does not because it is within ecu parameters but your ass feels that the car hiccuped or moved or reacted or revved like it usually does ... as you mentioned above. Ive had another issue that threw a CEL ... but CEL code did not relate to the fault (showing misfire) but in the end after several clears and more CEL i finally get the code for the problem, which was the intake solenoids (there are two of them) were old (8 years and 260k kms old) not running 100%. They usually cause a ticking noise ( coming from the center front or driver side of the engine) and under high load a misfire and possibly also on a cold start affect how the engine sucks in air until ecu adjusts for the lack of.
The moral of the story... the car is getting old and so are its sensors and solenoid and other parts that can wear out. Im thinking now its time to change main O2 sensor .
Anything else you have come across that should be considered?
@arathol
 
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