Rough idle

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.

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.

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,

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?

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.

[quote:6be95cf385="legitimate007"]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.[/quote:6be95cf385]


No check engine light on. Where should I start should I try to clean the iac valve? where is the egr valve located?

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.

https://www.2carpros.com/how_to/how_to_tune_up.htm

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?

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?

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

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.

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

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!! ;-} )

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.

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?

Lets check the compression and injector on that cylinder-if it was a gas problem it will affect all cylinders.

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???

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.

Cool!!

She is bringing the car home this weekend from school, I'll have her stop by the mechanic and have him check out the compression and injector on that cylinder.

Thank you so much for the help. I will let you know how it goes after Friday's visit! ;-)

Thank you for suggestions - now I feel a bit more comfortable that it might be the Idle Control Valve.

I'll keep you updated with the results.

And I'll definitely look into the position sensor. Thanks Again!

Jumped time. put new timing kit in and now engine idles rough, it is kind of surging when in gear. I took timing cover back off checked time again it is good. why is it running rough?

awesome

The 2.5L is listed as an "interference" engine, so it likely has bent valves. The best test to identify that is a cylinder leakage test. If valves are bent, you will hear air hissing from the tail pipe and/or throttle body.

If so why? it has plenty of power when driving with no miss just at idle.

Many years ago I had a Dodge Dart with a 340 c.i. that I raced. It had a badly burned valve that I later found to be about one-fifth missing, (burned away). It did sound like an air compressor at idle, but it had all kinds of power. You can have valves that are leaking far less than mine was, but you have to remember, my idle speed was controlled with an adjustable screw. Yours is controlled with a computer that is expecting to see a steady vacuum reading at idle. Leaking valves will cause a reduction in vacuum and idle speed, then the computer will try to correct the idle speed while including that unknown variable in the fuel metering calculations. The electronic controls and the mechanical characteristics of the engine are fighting each other instead of working together. Most of the time the engine will not start or run with bent valves, but that depends on how much the timing belt jumped. You do not have to worry when it jumps one or two teeth, but there are some engines that cannot tolerate it jumping three teeth. If your timing belt broke while the engine was running, it is almost a certainty there are bent valves. (I have to add that my source has been wrong on at least one occasion. They list the 3.0L in my 1988 Grand Caravan as an interference engine, and I know it is not).

Sometimes you can get an idea of the condition of the valves by turning the crankshaft by hand, with a ratchet. It will start to turn hard when a piston comes up on top dead center on the compression stroke. If you know what "normal" feels like, you may recognize when it turns too easily. A helper may hear hissing at the tail pipe. You should never hear that at the throttle body. During the exhaust stroke when the exhaust valve is open, you can't turn the crankshaft fast enough by hand to make the normal hiss.

Since you are confident the belt timing is okay, I would do the cylinder leakage test on at least one cylinder. Also, consider that it is not uncommon on some engines for the dowel pin, (when that's what they use), to shear off the camshaft sprocket, then the sprocket turns on the camshaft. That makes cam timing late even though the sprocket is right on the money.

Engine Performance problem
1998 Mazda 626 4 cyl Two Wheel Drive Automatic

I have a Mazda 626 1998 4cyl with 106000 miles on it! Idling is rough as soon as I put a load on it. If I put the AC on, it stall! I changed the fuel filter, air filter , spark plugs, spark plugs wired, checked the EGR, cleaned both the Idle Air Control and Mass Air Flow sensor. The IAC was a little black but I do not see any improvement after cleaning it! Is it because you are supposed to reset the computer and if yes how do you do it? What else could be wrong??? Please help I need AC (in Tucson AZ).

Inspect and test the throttle position sensor's closed and wide open throttle voltages, also check the PCV valve and also check if it has an idle up solenoid might not be increasing the rpm when AC clutch engages the compressor

Thanks Rasmataz. Any trick to test throttle position sensor manualy? How do you check the PCV Valve because when I pull it it has suction?

Back probe the TPS reference voltage should give 5volts and also the return signal wire should gradually increase voltage to that amount in a linear way with no breaks -

PCV valve -shake it should rattle if not clean it

I have a 1998 Mazda 626 with 124,000 miles that purred like a kitten until 2 months ago. Since then the car has idles rough and the check engine light has come on several times. I had the 02 sensor fixed, the MAF, the air filter changed, the plugs and expensive wires. I have used STP and fuel injection cleasner and nothing has worked. I have service comments from a shop which state: No Codes! Will Start With Intake-Gasket. Please advise if this could possibly be my problem. The price is &288.00. I cannot afford to fix anything else but the problem.

does the idle issue happen before or after the car warms up? or is it all the time? could be a vacuum leak or a temperature sensor malfunction.

thank you so much I'll try that. really appreciate your feedback.

I'm having the same issues with a 98 626lx at appx the same mileage. Check engine light had come on with an Idle Control Valve error code.

Where you able to fix the issue? If so, was it a vacuum leak?

Ive recently changed the transmission in my 1998 Mazda 626 and now i'm having cooling problems. Ive changed the thermostat and replaced one of the fan motors on a radiator fan (it was burned out). I have a small leak in the radiator on the side of the engine where the air intake is. The car will run at normal temperature for 20-30 minutes before it starts over-heating then shoot right up to the red. The water levels have been anywheres from normal to way low when the car overheats. Also, the car has started to idle real low, at about 500 rpms and the car wants to shut off when standing in idle. Any solutions or opinions of what all may need to be changed is much apreciated.

Replace the radiator!!! would be the first thing i would do,if it has a leak,then you may see the car acting funny! I remember this happened to me when i had a chevy nova 1987 model (love the car which was basically a toyota corrolla) but the radiator had a small leak/crack, had to change the whole thing out and it worked fine afterwards! That may be a good start to it!

The car idles rough when in gear, idle has been adjusted but still idles rough. I saw a previous answer about cleaning the throttle body and the IAC,would this cure the problem.

Try cleaning it and see what happens and also go here: https://www.2carpros.com/articles/engine-misfires-or-runs-rough

My car idles rough normally and it takes off sluggish what are some tips that could be performed to fix this problem. The plugs and wires are only 6 months old.