Mazda5 1.8 MT revs up by itself

[deisz001]

Hi all,

Yesterday I had a rather unpleasant experience with my 2005 Mazda5: It started revving up by itself. For some reason it had determined to rev up once the rpm dropped below about 1800. It then revved up to about 2300, slowed down and then it all started again. Just like I was pushing and relieving the accelerator every 2 seconds...
It did this while driving at about 2000 rpm: it accelerated a bit and then slowed down again. When I floored the clutch-pedal, it continued doing this. The motor was warm: I had just driven about 40km at 100km/h.
After I shut down the engine and restarted it, this behavior has disappeared...

What could have been wrong?

Kind regards, Stefan.

P.S. I'm a non-native English speaker, so please excuse me for any mistakes in my technical English...

 

[Robotazky]

I'm assuming that the '05 Mazda 5 is like the '06+ models in North America and that the 1.8L engine in your car is drive-by-wire (DBW) like the North American 2.3L.

If the car is not DBW, there is an excellent chance that the cable is sticking inside the sheath that surrounds it. I have a '93 Mazda MX3 that did exactly what you're talking about. I sprayed silicone lube down the cable and it stopped. The heat from the engine would cause more friction inside the cable sheath and it would stick in hot weather.

It sounds like you have an electronic part feeding your computer bad data or the computer was bugging out. Since you say it stopped doing it after you turned the car off, I would guess that you had a software glitch that is resolved. You really can not know how to proceed unless it happens again. If the computer (ECU) is going bad, then the frequency of occurrences will increase, typically.

If and when it does happen again, confirm that it stops by turning the car off and starting it again. You may want to drive it while it malfunctions for a while so that you can provide more descriptive information to others. It will not tear the car up to drive it like that unless it causes the car to lunge forward and possibly cause an accident.

I would then clean the mass air flow (MAF) sensor with the proper spray fluid from the auto parts store. I would also make sure the air filter is clean. If the car has over 60,000 miles, I would change the plugs.

If it keeps happening, you will need to wait for the "check engine light" (CEL) to light up or just take it to the dealer to pull the CEL codes from the computer. If I had to guess at an electronic issue, I would guess it's the MAF or the crankshaft position sensor.

Let us know if it happens again and be ready to describe it in better detail if possible.

 

[deisz001]

Wow! Thanks for the elaborate reply! It's much more informative than my dealership was able/willing to tell me. Last monday, my car had it's 6-year maintenance service at the dealer and they have not been able to find any fault. They suggested to change the plugs, but the car has only had 56.000 km (35.000 miles) and they said the plugs are normally changed at 120.000 km, so they were hesitant on that. Since I also think it must have something to do with a bad sensor readout or a bad computer, I decided not to have the sparks replaced (it would have cost me about 150 euro).

In the meantime I've ordered one of those ELM327 bluetooth OBD readers. I use an Asus R2H as a carpc, so when the car starts acting up again I hope I will be able to gather a lot of data. When it happens again, I will post it here.

Kind regards, Stefan.

 

[flcruising]

Good information Robotaz. I would also suggest you get some electronic parts cleaner and go crazy on the MAF sensor. You do not have a CEL as of yet? Can you confirm whether you have a cable throttle?

 

[Silentnoise713]

Hi all,

Yesterday I had a rather unpleasant experience with my 2005 Mazda5: It started revving up by itself. For some reason it had determined to rev up once the rpm dropped below about 1800. It then revved up to about 2300, slowed down and then it all started again. Just like I was pushing and relieving the accelerator every 2 seconds...
It did this while driving at about 2000 rpm: it accelerated a bit and then slowed down again. When I floored the clutch-pedal, it continued doing this. The motor was warm: I had just driven about 40km at 100km/h.
After I shut down the engine and restarted it, this behavior has disappeared...

What could have been wrong?

Kind regards, Stefan.

P.S. I'm a non-native English speaker, so please excuse me for any mistakes in my technical English...

I think Gremlins are starting to find comfort in the Mz5 -j/k

I would look at the MAF sensor first. If the behavior returns and becomes consistent, I would bet you have a vacuum leak. What you described sounds like idle surge which is a classic vacuum leak issue -easy fix, you just have to find the leak. However, a 6yr old cars tubing and rubber components (mileage is less of a factor) should not be leaking Did you do any service or mod to the car lately?

 

[deisz001]

About the drive by wire: I checked it today and it seems that the accelerator is directly coupled to the actual throttle that goes into the engine. With the car key removed, when I press the accelerator, the throttle turns. So I guess it can't be drive-by-wire. Am I correct in that?
Is the MAF sensor something to be cleaned easily? Although I'm quite handy with all sorts of do-it-yourself projects, I haven't done anything more to my car than checking the oil-level and charging the battery...
I have not done any service for a year (except for inflating the tires . The day after this problem occured, I had an appointment with the local dealer for it's 6-year maintenance service. (It has had all the Mazda-advised maintenance services) There haven't been any technical mods to the car.
I haven't yet had a CEL.

 

[flcruising]

You definitely have a cable throttle. This brings up another cleaning you should do, and that would be to the throttle body itself. All you need for that is some carb or brake cleaner.

Definitely clean the MAF sensor which is located on the intake hose side of the air box that holds the engine air filter. If you can post a picture of your engine bay, I can label it for you if you like.

Your throttle body has a part that we don't have on our drive-by-wire system called an idle air control (IAC) valve. This is essentially a plunger that the PCM controls to allow a certain amount of bypass air around the throttle blade. These can get gummy and often stick causing symptoms you describe. I suggest removing both the MAF sensor and the throttle body to perform the necessary cleaning. Sometimes the IAC valve can also be dismantled to allow a new application of lithium grease inside on the shaft of the plunger. Depending on the type of intake manifold your car has, the throttle body may require a new gasket or at least some RTV (silicone gasket maker) for re-installation.

 

[Robotazky]

I would hold off on buying a code reader unless you are getting codes, which I don't recall you indicating.

My first effort would be to clean the MAF sensor. Then take your throttle cable off where it connects to the throttle body (the part that moves when you push the pedal down) and patiently spray silicone lubricant down into the cable. Hold the cable up so that the fluid is running down it. I think your statement about pushing the pedal down and it didn't change the behavior certainly indicates an electronic problem, but a binding accelerator cable could be throwing an electronic part out of its comfort zone and causing problems.

Keep us posted on your progress.

 

[Robotazky]

You definitely have a cable throttle. This brings up another cleaning you should do, and that would be to the throttle body itself. All you need for that is some carb or brake cleaner.

Definitely clean the MAF sensor which is located on the intake hose side of the air box that holds the engine air filter. If you can post a picture of your engine bay, I can label it for you if you like.

Your throttle body has a part that we don't have on our drive-by-wire system called an idle air control (IAC) valve. This is essentially a plunger that the PCM controls to allow a certain amount of bypass air around the throttle blade. These can get gummy and often stick causing symptoms you describe. I suggest removing both the MAF sensor and the throttle body to perform the necessary cleaning. Sometimes the IAC valve can also be dismantled to allow a new application of lithium grease inside on the shaft of the plunger. Depending on the type of intake manifold your car has, the throttle body may require a new gasket or at least some RTV (silicone gasket maker) for re-installation.

All good points.

 

[Heat]

Had a question - can you get the cargo van modification in the Netherlands? See Post #14 in this thread:

http://www.mazdas247.com/forum/showthread.php?t=123680189

He was saying it was only available in Denmark, I was wondering if it was available in other countries and the Netherlands is close...

With regard to your English - it's great. Better than many native speakers I know, and much, much better than my wife's written English (she is from South America).

Here is a part of her last email to me:

Well Mike . A reletionship is for TWO ,two that love ,respect,enjoit toguether... is something that we dont have in our reletionship.Thanks for give me my two wonderfoul kids.I promese my self no one is going to play with my feelings or hurt me.Goodbye my best for you ... ADIOS ADIOS PARA SIEMPRE.

The text is pretty subtle, but I don't think she's happy.

 

[deisz001]

flcruising: You definitely have a cable throttle. This brings up another cleaning you should do, and that would be to the throttle body itself. All you need for that is some carb or brake cleaner.

How should I clean the throttle body? Just spray it with a cleaner? Or does it need to be removed like you described? It seems quite difficult to remove. (see the attached picture )

flcruising: Definitely clean the MAF sensor which is located on the intake hose side of the air box that holds the engine air filter. If you can post a picture of your engine bay, I can label it for you if you like.

I attached a picture of what I think is the MAF sensor.

Can I just unplug the connector (after I disconnected the battery), remove the two screws and then pull the sensor out?

Robotaz: I would hold off on buying a code reader unless you are getting codes, which I don't recall you indicating.

I ordered one on Ebay that's only 18USD, so that's quite cheap. Is there another reason than money to not buy a code reader? As far as I know, even a cheap reader will be able to report a lot of data, including the MAF sensor readout and will allow me to see if there are any strange readings that could indicate a sensor malfunction.

Heat: Had a question - can you get the cargo van modification in the Netherlands? See Post #14 in this thread:

No, I've never seen it before. I'm sure it's not available in the Netherlands. I also did a search on the Danish sites and haven't found it there either, so maybe this is some nice custom work? The name of a Danish Mazda dealer is on the license-plate-bracket in one of the pictures, so maybe you can contact them for details?

At this moment, the car runs very smoothly. I can definately tell it has had it's maintenance service at the dealer. I'll keep you updated when the problem occurs again. (And now I am prepared
Thanks a lot for your help! It is much appreciated!

 

[Robotazky]

To clean the throttle body (TB), disconnect the air intake tube from the throttle body. With the TB closed, spray TB cleaner into it. Wipe away cleaner. Then, open the TB with the lever where the throttle cable attaches. Spray into the TB, minimizing the amount that sprays into the intake. Wipe it down. There will be residue on the bottom where the plate closes, behind the plate. Try to wipe the backside of the plate. If it's all clean in that area, I would assume that the TB is not your problem.

Yes, you can just pull the sensor out in the manner you mentioned. Spray it out. I shake out the residue so that dirt comes out more efficiently and so that it will dry out more quickly. You can't spray too much so make sure you clean it well. Also make sure that it is completely dry before re-installation.

I have never seen a code reader that does anything more than display error codes that the computer stored. You will not get more data than that. At $18USD, you can expect a very minimal reader, which is OK, but it will not provide additional computer data beyond thrown codes. Have you seen a check engine light (CEL) on the dash?

 

[deisz001]

OK, thanks for the description. Now I have to get some good cleaning sprays...

The code reader is advertised with the following features:
* Read diagnostic trouble codes, both generic and manufacturer-specific, and display their meaning (over 3000 generic code definitions in the database).
* Clear trouble codes and turn off the MIL ("Check Engine" light).
* Display current sensor data, including:
* Engine RPM
* Calculated Load Value
* Coolant Temperature
* Fuel System Status
* Vehicle Speed
* Short Term Fuel Trim
* Long Term Fuel Trim
* Intake Manifold Pressure
* Timing Advance
* Intake Air Temperature
* Air Flow Rate
* Absolute Throttle Position
* Oxygen sensor voltages/associated short term fuel trims
* Fuel System status
* Fuel Pressure

So I guess it must be able to show the MAF sensor data. But seeing is believing... I'll post my experience with this reader in a separate thread.

 

[flcruising]

The ODB reader you describe is very similar to my laptop scanner you can see screenshots of here - http://www.obddiagnostics.com/ScrnShot/Winscreen.html

The limitation is the in-ability of selecting sensors individually and displaying their inputs. Essentially you are seeing what the computer interpolates, not raw sensor data like voltage. The scanner will be fun and helpful at times, but not really a diagnostic tool besides pulling DTC's.

You can clean the t/b like Robotaz describes, but I've always removed it so I can hit it from every angle with cleaner. Also, I'm used to some t/b's that have vacuum ports and require some special attention to make sure all is well with them too. And as you suspect, removal eliminates the risk of washing the dirt further into the intake.

 

[Robotazky]

The ODB reader you describe is very similar to my laptop scanner you can see screenshots of here - http://www.obddiagnostics.com/ScrnShot/Winscreen.html

The limitation is the in-ability of selecting sensors individually and displaying their inputs. Essentially you are seeing what the computer interpolates, not raw sensor data like voltage. The scanner will be fun and helpful at times, but not really a diagnostic tool besides pulling DTC's.

You can clean the t/b like Robotaz describes, but I've always removed it so I can hit it from every angle with cleaner. Also, I'm used to some t/b's that have vacuum ports and require some special attention to make sure all is well with them too. And as you suspect, removal eliminates the risk of washing the dirt further into the intake.

Not to be adversarial flcruising, but I wouldn't recommend that a person asking how to clean a TB actually take it off, personally. I also wouldn't recommend spraying cleaner in the ports. The cleaner will eat right through the plastic bellows if there's an IAC. I have some round files that are very small in diameter that I poke into the ports with a cotton cloth with just a little bit of the cleaner on it. If you start getting into taking the TB off and cleaning all of the ports out, you need to have a good idea that this is the problem. OP, I wouldn't do more than clean it on the car until you have exhausted some other options. Again, that's my suggestion and you are welcome to do whatever you wish. I just don't have time for extra work on cars and assume others do not as well.

And honestly, if your car needs the TB cleaned with 35,000 miles, you have way bigger problems to figure out. I suspect you will take the air tube off and see perfectly clean metal. If you open the butterfly valve and the body is spotless where the valve closes, move on to the other options.

 

[flcruising]

I agree, though I've never had an issue with carb cleaner eating any plastic pieces...

Definitely start with the MAF sensor and report back. Keep fingers off all parts of it but the base (the outside part you see in the picture). I haven't looked at mine, but if it's a hot-wire type, don't blast it up close with cleaner either.