Idle Issue

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2008 Mazda5 GT
Been having idle (vibration) issues for a while now. Only occurs when the car in Drive/Reverse (drivetrain engaged). RPM is not erratic and the car otherwise idles fine in Park/Neutral and drives/accelerates fine. I suspect either air or fuel issues but there’s no check engine light. Vibrations can sometimes be very violent and at times do not occur!?! This is starting to annoy me… Anyone else experience this? Something else to check?

Took out EGR, cleaned/scrubbed
Took out throttle body, clean both sides
Took out and test purge valve solenoid
Took out and cleaned both EVAP solenoid
Took out and cleaned MAF
Open bottle of propane to check for vacuum leak
3 OEM mounts (granted not standard fit, per say) < 10K miles
New spark plugs < 500 miles
Engine air filter is not clogged


Some other things that come to mind is PCV but that’s a b*tch to get to. Fuel injector blockage but full injector clearing service can get expensive and requires down time (send out injectors, no local place). I do feel my avg. MPG has dropped. I also think perhaps it is motor mount but that does not explain why it happens sometimes but not others. Also, it is b/c of vibrations that lead me to replace all motor mounts ~10K ago. Is there something else that could be a cause? Aside from PCV, have I exhausted all "air" side of the problem? I think the next to check would be "fuel". May try to use some fuel additive/injector cleaner to see if that helps. IF this improves the situation, may point me towards fuel side and the lead culprit may very well be dirty injectors...
 
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Have you changed also motor mount under battery too? May be a clutch problem...I have same problem when I go over a ramp in reverse mode...Or a sloping road in reverse mode
 
Based on the behavior I’m observing, I do not think it is motor mounts. Also, I replace all 3 mounts not too long ago when it wasn't as bad suspecting mounts. https://www.mazdas247.com/forum/sho...-Motor-Mount-Experience-Recommendations/page4

With the car at operating temp, when I come to a complete stop (in gear, brakes applied, drivetrain drag) the car idles perfectly fine for ~1.5 secs then RPM dips slightly and car vibrates. It’s as if it is starving for air or fuel and my MPG seem to have taken a noticeable hit (beyond winter gas blend). What’s strange is that at times, it would idle ok for more than 1.5 secs. I also wonder/suspect if the TB is going bad. The electronic throttle bodies auto adjust for idle conditions (why ideal learn is important and there is no TPS adjustment). The electronic sensor determines the plate position when idling and I wonder if the sensor is going bad (bad resistance)? Pure speculation b/c no CEL.

After watching this, the TB is pretty simple inside. Without a CEL, this is just speculation…
https://www.youtube.com/watch?v=FDpUo3UPmto&t=38s


The car is nearing 100K and running cheapest regular gas. The EGR has a nice thick carbon build up. I just ran a bottle of Techron (and did some other stuff) and it seem to improve a little. It does not shake as violently. Will run another tank with Gumout Regain and run Seafoam intake cleaning. Hoping for best..
 
Have you reset the ECU yet to force a re-learn? TB seems to me to be a clear possibility. 01 Volvos had an ETM (electronic throttle module - I think) that went bad and caused all sorts of fuelling issues like insane vibrations. Another thought is O2 snesors, but since they are emissions, any type of error from those should throw a CEL. I am curious how long it would take to re-learn this bad idle behavior if you pulled the batt cable and grounded the system.
 
Passenger side top motor mount. I had the exact symptoms you described. Vibration while in drive at idle, switch to neutral at stop lights - goes away. That motor mount is a common REPEAT failure.
 
Totally agree with the previous post. Passenger side engine mount + let your car re-learn the idle RPM (disconnect the battery, connect it again, start the car, let it idle for 5 minutes).
 
I have not investigated this further. Will look into it more this/next month. Plan is to check PMM and RMM (not TMM bc I'm too lazy to take everything off to check that). Run a bottle intake cleaner, PCV next, then new TB, lastly reman injectors; temped to move injectors up bc poor MPG. I still think it's the PCV or TB but will do frugal checks first. It is bearable and random so I'm not motivated.
 
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I have not investigated this further. Will look into it more this/next month. Plan is to check PMM and RMM (not TMM bc I'm too lazy to take everything off to check that). Run a bottle intake cleaner, PCV next, then new TB, lastly reman injectors; temped to move injectors up bc poor MPG. I still think it's the PCV or TB but will do frugal checks first. It is bearable and random so I'm not motivated.

I'm very curious if you've resolved this. I've had similar issues, though with minor shudder and idle surging. Seems to correspond with AC cycling.

Just bought an OEM PMM to try this weekend.
 
Was hoping this would go away if I leave it alone :p (/s)

Yesterday was a nice day to explore a bit.
Took out PMM --> in great shape (replaced with revised OEM not too long ago)
Visually inspected TMM --> looks really good (replaced with OEM not too long ago)
Didn't bother to check RMM b/c I really don't think it is a mount issue. That and it a more likely the softer mounts will give before this solid rubber mount. I still get the sense it is fuel or air. I moved injectors up and put in a reman. set (flow matched/ultrasonic cleaned/new seals). Nope, that's not it either but the car does pull smoother. I should add that I test the resistance of the all coil packs and they all have similar reading. I think I can eliminate fuel. I think it is now down to air (or emissions).

Trying to pin this down without a CEL is a real pain in the butt... I think I may swap in a reman. TB (not that expensive). I've been researching a lot into these crappy FoMoCo TBs and they seem to have common issue with the electric sensor going bad (corrode ground inside). Next possibilities is PCV (highly likely) but I dread having to take apart the IM. My worst case/fear is failing torque converter. Thoughts?


Does anyone have an used/broken/unwanted TB laying around?
 
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Throttle body!

Put in a reman TB (Cardone), idle learn - still rough. After a few hundred miles for PCM to also learn hwy and high load parameter, car finally idles normal again - 850-900 RPM when Parked/Neutral (no load) AND in Drive/Reverse (drivetrain load). Before TB, load would drop RPM to about 550. I think the issue is all electrical within the TB where the TPS is not proving enough air under load.

No I hear a rattle coming from the deep behind the dash... never ending.
 
Well this is strange... one off occurrences two days back and today morning, during one trip (but not multiple times within the day!), it idle down to 550-600ish again while stopped in Drive. However, there is one HUGE difference. Prior to the reman TB, the RPM would go back up to 850-900'ish if I shift it to Park or Neutral - NOT this time. When it happened, it stays consistent at 550-600ish RPM no matter the gear I am in!?... Also, RPM would stop at 900 for a brief sec, then slowly (gradually watching it) drop down to 550-600 but stays there no matter the gear I'm in. Now I beginning to think PCV again. could it be that my long drive created enough heat/pressure to unclogged it for a while but now is building back up? when I replace the TB, I noticed the IM was nicely coated with what appears to be oil residue. Crazy thing is, it does idle fine -sometimes-. I wish this damn car would just throw a CEL already...
 

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