Motor Stumbles

[jwehrheim]

The motor stumbles and hesitates periodically. Happens while driving and sitting at the light.

Any ideas what might be causing this?

 

[Megazuel]

Do you have a MIL on? any pending codes? EGR issues are real common, as are coil packs taking a crap. What is the state of tune? How many miles on it? Are the plugs original? Are the throttle bore and IAC all coked up?

 

[jwehrheim]

Some times the MIL (Check Engine Light) will come on, but then go off. New Timing belt, spark plugs. Approx 87,000 miles. Not sure on the IAC (what is an IAC) and throttle bore. I was thinking of cleaning the mass airflow sensor.

 

[Pro5.0]

Just throwing this one out there, o2 sensor...mine has displayed similar issues. The hesitation and stumbling. The CEL said it was the downstream o2 sensor, but now the CEL is not on. I don't have the stumbling while at a light sitting there though, which may indicate it's not the same issue. Worth checking into though.

 

[Megazuel]

Some times the MIL (Check Engine Light) will come on, but then go off. New Timing belt, spark plugs. Approx 87,000 miles. Not sure on the IAC (what is an IAC) and throttle bore. I was thinking of cleaning the mass airflow sensor.

IAC= Idle air control valve, mounted on the throttle body. Allows air to pass around the throttle plate when you have your foot off the gas. It's what keeps the RPM's up on cold starts. If the IAC or throttle plate are gummed up with carbon, they can cause all sorts of issues. Take the intake tube off the throttle body and look inside. Clean it out with a rag and some throttle body cleaner (2+2 works well, just don't spary a shitload of it into the intake, spray it on the rag and wipe the crap out). What codes are being set with the MIL?

 

[Megazuel]

Just throwing this one out there, o2 sensor...mine has displayed similar issues. The hesitation and stumbling. The CEL said it was the downstream o2 sensor, but now the CEL is not on. I don't have the stumbling while at a light sitting there though, which may indicate it's not the same issue. Worth checking into though.

Not that anything is possible (I've seen some bizarre stuff), but a downstream O2 will not normally affect drivability. Its main purpose is testing the cat. Some vehicles also use it for baseline fuel adjustments based on what they are seeing coming out of the cat (Hondas, Chryslers). Its something you would need a scan tool to see, but at the same time, if the downstream O2 is making a big adjustment to fuel trims, you should probably see a noticable change in fuel economy. Plus, I don't think Mazda uses this strategy anyway.

 

[jwehrheim]

Will a Engine Code Analyzer pick up codes even if the check engine light is not on? I don't have one, but a friend does that I can borrow.

 

[fishdonotbounce]

clean your egr valve. There's a how to on here.

 

[Pro5.0]

megazuel...it sounds like his car is still driveable, but hesitates...which is pretty similar to mine. That's the only reason I suggested checking into it.

 

[Pro5.0]

I was searching for some things and came across this...check it out jwehrheim. I didn't get a chance to read through it, but I'm sure it has your fix. The guy had the same problem.

http://www.mazdas247.com/forum/showthread.php?t=123701316&highlight=spark+plug+gap

 

[jwehrheim]

Yes, it only happens maybe once a day. The car is very driveable, but it will all of a sudden stumble. Feels like it will stall, but doesn't. It will happen just idling or driving down the road. I will check everything that was outlined on the link. I have new plugs, timing belt, fuel filter.

 

[martispeed]

+1 on the egr...

 

[pasadena_commut]

Yes, it only happens maybe once a day. The car is very driveable, but it will all of a sudden stumble. Feels like it will stall, but doesn't. It will happen just idling or driving down the road.

Mine stumbles exactly once per day - apparently on the transition from open to closed loop. It is very evident because I usually drive almost exactly the same route so it tends to happen while waiting at the same light. The RPMs drop a couple of hundred for a fraction of a second and then come back up. It isn't evident in the afternoon going home, possibly because then the transition happens when the car is moving along, and a fraction's second drop of a couple of RPM isn't evident over the road noise.

So far the only time mine ever stumbled enough to notice while cruising along was when the spark plug wires were bad.

 

[Megazuel]

megazuel...it sounds like his car is still driveable, but hesitates...which is pretty similar to mine. That's the only reason I suggested checking into it.

No problem, and again, I have seen O2's, mainly upstream (GM's mostly), cause drivability issue. On the other makes I mentioned (esp. Chrysler), the downstream O2 can definitely can performance issues. I have learned all too well that anything is possible on any vehicle, even if it makes no sense.

 

[Pro5.0]

Yeah, i understand. I hope you didn't think i was being a prick or anything with my comment. I have to agree, anything is absolutely possible when something is wrong.

 

[jwehrheim]

Thank you for everyones help. I cleaned the EGR and Mass Air Flow. So far so good. Motor has improved pickup/acceleration and no more stumble.

It is fairly easy except trying to get to the two bolts on the EGR.

 

[jwehrheim]

I have cleaned the MAF and EGR. Seemed to help for a couple of days, but has now come back. I have also determined that it is only occuring during an idle situation. Sitting at a stop light or off throttle crusing to a stop light.

Any other ideas?

 

[Megazuel]

I have cleaned the MAF and EGR. Seemed to help for a couple of days, but has now come back. I have also determined that it is only occuring during an idle situation. Sitting at a stop light or off throttle crusing to a stop light.

Any other ideas?

Mine was doing the same thing off and on for a few months, cleaned the EGR several times after I know it hung on me and caused some real bad misfires. I finally bit the bullet and got the canadian version of the EGR valve, popped that and two new coil packs on and the car runs like a dream. Not only is the idle so much smoother and more stable, but I no longer get the rpm drop and surge at cruise. I think these EGR valves are not only getting stuck at full open when the PCM commands a EGR test but also not fully seating at times, causing a mixture issue at lower speeds. I wish I would have put the canadian EGR on months ago, and for some reason it's actually cheaper than the US version that is so prone to problems (figure that one out...)