Rough idle

Tiny
DARIN YOUNG
  • MEMBER
  • 2000 MAZDA 626
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 98,000 MILES
Car has rough idle and no power when in gear smell gas.
Saturday, March 25th, 2017 AT 8:37 AM

76 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Scan for codes and check fuel pressure with a gauge auto parts rent it. If it is a random misfire it may be due to low fuel pressure. If it is a a misfire code do not buy parts for it as it you may be replacing good parts so have a mechanic look into it to see what is the cause as it can be an injector, sensor or a basic engine problem.
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Saturday, March 25th, 2017 AT 9:53 AM
Tiny
CRACKCORN
  • MEMBER
  • 6 POSTS
  • 1999 MAZDA 626
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 120,000 MILES
When my 99 mazda 626 is at operating temp it idles rough and stalls sometimes in park, when at a stop light in drive it idles better. When I unplug the mass air flow sensor it idles fine! Should I replace the maf sensor? Some one told me it could be the air temp sensor in the airbox. Replaced the plugs, pcv valve and hoses.
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Sunday, January 5th, 2020 AT 6:49 PM (Merged)
Tiny
LEGITIMATE007
  • MECHANIC
  • 5,121 POSTS
Yes, good observation, with the mass airflow sensor, also you should have a check engine light on, no? If so, just have it scanned at autozone, it will reinforce your observation, and if not, it will atleast give us something definite to go on, just jot the codes down and bring them to me for further diagnosis, but very good, on your finding.
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Sunday, January 5th, 2020 AT 6:49 PM (Merged)
Tiny
CRACKCORN
  • MEMBER
  • 6 POSTS
I replaced the mass air flow sensor and still the same thing! I'm not sure what is is. If you unplug the maf sensor still it runs better! Could it be a vacuunm leak?
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Sunday, January 5th, 2020 AT 6:49 PM (Merged)
Tiny
LEGITIMATE007
  • MECHANIC
  • 5,121 POSTS
Yes it could be a vacuum leak amongst several other possibilities, if there is a check engine light on, bring it to autozone or your local parts store and have it scanned, it will make it so much easier and narrow the possibilities down, other possibilities, can be the egr valve, the idle air control valve, the iat(idle air control valve) that sensor in the air box.
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Sunday, January 5th, 2020 AT 6:49 PM (Merged)
Tiny
CRACKCORN
  • MEMBER
  • 6 POSTS
No check engine light on. Where should I start should I try to clean the iac valve? Where is the egr valve located?
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Sunday, January 5th, 2020 AT 6:49 PM (Merged)
Tiny
LEGITIMATE007
  • MECHANIC
  • 5,121 POSTS
I would start there, and clean the throttle body if you havent already. I have a diagram, I am assuming this is the 2.0 if not then let me know. Also the hose/accordian hose that is connected from the airbox to the throttle body look at it really well and see if there are any cracks or holes in it, this will cause you some problems.
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Sunday, January 5th, 2020 AT 6:49 PM (Merged)
Tiny
LEGITIMATE007
  • MECHANIC
  • 5,121 POSTS


https://www.2carpros.com/forum/automotive_pictures/88091_iac_626_20_1.jpg

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+2
Sunday, January 5th, 2020 AT 6:49 PM (Merged)
Tiny
LEGITIMATE007
  • MECHANIC
  • 5,121 POSTS
https://www.2carpros.com/how_to/how_to_tune_up.htm
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Sunday, January 5th, 2020 AT 6:49 PM (Merged)
Tiny
CRACKCORN
  • MEMBER
  • 6 POSTS
I cleaned the iac valve and the egr valve. The egr valve was filthy! I put a new throttle body gasket on and started t up and went for a 20 minute drive. It idled great!Plus the exhaust wasn't making a puffing sound anymore. When I was driving it was sputtering a little bit. Is this because the computer needs to reset the settings?
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Sunday, January 5th, 2020 AT 6:50 PM (Merged)
Tiny
CRACKCORN
  • MEMBER
  • 6 POSTS
NEVERMIND! I took it to the store and wouldn't you know. At the stop light it started loping again, and I floored it and it backfired a little. The popping in the exhaust is back. Does a mechanic do a reliable vacuum test?
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Sunday, January 5th, 2020 AT 6:50 PM (Merged)
Tiny
LEGITIMATE007
  • MECHANIC
  • 5,121 POSTS
Yes, I know your frustrated, but it will get fixed, its not as easy as some people think. Check the mapp sensor, also see if the accordian has any cracks in it. And of course the catalytic, I dont remember if you said you had that looked at
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Sunday, January 5th, 2020 AT 6:50 PM (Merged)
Tiny
CRACKCORN
  • MEMBER
  • 6 POSTS
Thanks for your help! I broke down and got it checked for a vacuum leak, and the intake manifold gasket and the injector orings needs replacing. He is charging me 300 for both things.A coouple of garage mechanics quoted me at 200 plus parts. Do you think this is a fair price?I guess its worth it to get it off my mind!Thanks again.
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-2
Sunday, January 5th, 2020 AT 6:50 PM (Merged)
Tiny
LEGITIMATE007
  • MECHANIC
  • 5,121 POSTS
Yeah, thats a good price, it is kinda painstaking too, to get these done, so rest assured your good to go. Awesome, keep me posted as how your vehicle is doing afterward, we are always here for ya.
Jody
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Sunday, January 5th, 2020 AT 6:50 PM (Merged)
Tiny
MNDANDREWS
  • MEMBER
  • 3 POSTS
  • 1998 MAZDA 626
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 14,000 MILES
My daughter drives this car while she is away @ college. We recently replaced her timing belt and water pump. When we picked it up from the mechanic, we were told one of the engine mounts was broken, the car would run, but it would be rough while in gear but not moving (say like at a red light). Boy was it rough. We had the engine mount fixed, but it is still rough while in gear and stopped (again, red light) but much improved over what it had been. When the car is moving it is smooth and sweet. Lately she has had a check engine light come on and the auto 'zone' type stores tell her she has a mis-firing 3rd cylinder. We have all new spark plugs and wires. I put some slick 50 fuel injector cleaner in it about 300 miles ago. Are these two things related? Could the rough idle be a transmission problem (it's about the only thing I have not fixed/replaced on this car yet! ;- )
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Sunday, January 5th, 2020 AT 6:50 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Misfire at cyl no.3 -check the compression and injector on that cylinder

Engine misfiring can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.
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Sunday, January 5th, 2020 AT 6:50 PM (Merged)
Tiny
MNDANDREWS
  • MEMBER
  • 3 POSTS
So you don't think it is the transmission? That would be a relief!

Besides the fuel injector cleaner, what do you recommend for my next step? The spark plugs and wires are new with in the last month. It just passed it's safety and emissions inspection too. (Passed the day before the engine light came on, and 5 days after the code had been previously cleared.)

We get the 85 octane gas. Because of her high mileage should we buy the higher octane gas?
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Sunday, January 5th, 2020 AT 6:50 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Lets check the compression and injector on that cylinder-if it was a gas problem it will affect all cylinders.
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Sunday, January 5th, 2020 AT 6:50 PM (Merged)
Tiny
BEAU123
  • MEMBER
  • 4 POSTS
  • 1998 MAZDA 626
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 125,000 MILES
I'm trying to determine the cause of a rough idle. The check engine light came on and a mechanic traced the codes to the Idle Control Valve, however, I've been noticing on forums that this model is particularly susceptible to vacuum leaks that can cause rough idling. I've also noticed under other threads that a boot should be inspected for cracks, however, there is conflicting information as to which boot should be checked.

Note - Before the check engine light came on the idle fluctuated enough that car would almost stall at traffic lights. At that point the mechanic manually brought the idle up for a quick fix (the light came on a few weeks later).

Furthermore, if the A/C is on at highway speeds, the car's power seems to hiccup sporadically. Not sure if this is a related issue or not.

Any suggestions?
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Sunday, January 5th, 2020 AT 6:50 PM (Merged)
Tiny
LEGITIMATE007
  • MECHANIC
  • 5,121 POSTS
A vacuum leak would generally cause a high idle. Although you could have a vacuum leak, I don't believe that is what is causing the rough idle and the fact that your car wants to shut off at traffic lights. Check/change the idle air control valve and for good measure, check your vacuum hoses. That hicuup while at highway speeds could be an indication of problems soon to be, crank position sensor. Sometimes things hit all at once.
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Sunday, January 5th, 2020 AT 6:50 PM (Merged)

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