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Mass Air Flow Sensor

A few weeks ago I posted a thread about my '01 Corolla stalling when first started (see O.P. below). It's now been to the shop several times and the latest thing they've thought it might be is the mass air flow sensor. However, this is an expensive piece. What exactly does this do and is it a likely culprit?'

Thanks!

ORIGINAL POST

**************** Hello all,

I've got a 1.6L 2001 Toyota Corolla CE Auto with about 110,000km on it. The car is given synthetic oil every 3 months or 5000km, has had the tranny fluid changed at 90,000km, and is regularly and well maintained. The only major work done was my downlink cable was replaced about 7-8 months ago.

My last oil change was April 20 and everything was working great up until that point (the only thing it ever does is periodically (maybe once a month) it would not start right away (it always started on the second try ...like it either didn't get enough fuel or it flooded briefly?)). Anywho, shortly after my oil change (approx. May 4/5), I went to drive the car one morning and as soon as I backed to the end of the driveway, it stalled. I started it back up and it idled very low and rough ...similar to how my old carbuerated Jeep would idle (it was a p.o.s.). I thought nothing of it at first but a minute later I parked, got out for a minute to do something, came back to start it and it did it again. This had me a bit worried. Anyway, for the next few months until now, it has been doing this quite regularly - but not every time. Once the car has been running for a few minutes it is usually fine (only once or twice has it given me problems after being "warmed up" but it does periodically happen at red lights).

The car seems to idle OK in park but once it's in a gear, such as reverse when I first back out of my driveway, it idles like shit and sometimes stalls. The mechanics said it might be the changing weather or humidity but it seems unaffected whether it's cold out or warm out and has happened for several months now. I researched on the net and some sites have said to check the connections to the air filter (which was also replaced at the time of my oil change) but the mechanic rechecked the hoses and connectors and said they are fine. Last week I took it back in and they did an inspection and told me it was my plugs which were worn right out. I had them replaced with NGK plugs (total bill was $118 CDN for 4 plugs and labour ...is this normal?! When I did my Jeep plugs it was $20 and took my 20 minutes ...)

Anyways, the plug change didn't do anything to help. The car goes back in on Tuesday but if anyone has any suggestions before that that may save me time and money, lemme know!

Thanks

Reply to
griffin
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The mass air flow sensor sits between the air box and the throttle valve and is used by the engine to measure the amount of air entering the engine. The engine computer uses this measurement to calculate the amount of fuel to add to achieve the proper mixture. And yeah, they're quite expensive. This kind of intermittent problem can be very difficult to diagnose, and my first reaction to your post would be to advise you to find a different mechanic. Suggesting that the plugs are to blame for the kind of problem you're experiencing sounds like a shotgun approach, and wanting to replace the MAF sensor reinforces that. It certainly could be the MAF, don't get me wrong, but there are a lot of other components in the system that controls idle, and you need to find someone who understands them and someone who has the tools to do so. In order to really diagnose this you would need someone to plug in to the EFI computer and watch the values of parameters like the MAF sensor, air-fuel ratio sensors, idle air control valve, coolant temp sensor, etc... And more importantly you'll need someone who can make sense of it. Replacing parts that someone thinks "might be causing it" without any real testing is a very expensive way to go. But anyway, has the computer stored any codes for you? That would be helpful to know.

Reply to
qslim

some MAF require some cleaning with aerosol carb cleaners. you may save some money with this.

Reply to
EdV

On my 2002 Corolla -- which I believe yours is similar -- you can take a small philips screw driver and remove the MAF. Get some brake cleaner and you can gently clean the wire. Normally, this is done automatically as that wire I believe gets hot but I know on mine, it was pretty dirty. Now, about every 3-4 oil changes, I check the MAF to make sure it's clean. It's not hard to remove and not hard to clean. Just make sure you do not alter/break the wire in it. That can be bad.

When I had an issue similar to yours, it ended up being a dirty/ cracked fuel injector. I think I was using too much gas cleaner thinking I was doing a good thing when I was not.

Anyway, I would clean your MAF -- you can do it yourself.

Make sure your fuel injectors are clean and not dirty.

Make sure there are no holes in the airbox.

Once my fuel injector in question was replaced, problem went away.

Don't let them replace the IAC valve unless they *know* it's bad.

I also had them clean my throttle body, that's not hard to do either.

Reply to
mrsteveo

It seems to me that you need to find a better shop. If you want to continue "easter egging" the problem, try a fuel filter next. It almost certainly isn't the MAF since you are seeing a problem when the car is stone cold. Did they pull any codes from the PCM? Did they check the fuel pressure? Do they have any clue what they are doing? What the heck is a "downlink" cable?

Ed

Ed

Reply to
C. E. White

If you are able, clean off the MAF sensor (hot wire) using an aerosol spray. DO NOT TOUCH THE WIRES WITH YOUR HANDS OR CLEANING INSTRUMENTS! They are easily damaged and as you mentioned, an expensive part. Only some carb cleaners are advisable to use. I believe and use, like mrsteveo mentioned, that using a brake/electrical cleaner is less likely to leave any petroleum residue on the sensor which is definitely what you do not want, and some carb cleaners will. The instances that you have mentioned about the people working on your car do not instill confidence in me that they are doing you right.

Reply to
user

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