My car engine hesitates when I accelerate!
Quick and easy solution for curing the annoying hesitation, lag back feeling, stalling or whatever you wish to call it, which happens in some cars when accelerating.
(Note: While this article is based on Toyota Corolla late models, but this will also apply to most cars equipped with a MAF or flow meter.)
If you own a 2004, 2005, 2006 or 2007 Toyota Corolla or Toyota Rav4 and your car hesitates when you accelerate or it hesitates when driving, you should try the solution described here before doing any further troubleshooting, as this is a very common situation in the listed models and in many others not listed as well.
Below is a list of the behavior your car may show that tells that you should try this procedure before going to a mechanic or repair shop.
- If the accelerator is slightly depressed while the car is running and it lags or hesitates
- If after completely stopping the car, it hesitates when starting to move
- Engine power is below the usual level
- Sometimes check engine light turns on
- Low fuel economy and/or the smell of gas not completely burned
You should know that while those problems can be caused by several issues, including low quality or altered fuel or even a loosely tighten fuel cap, the most common cause is a dirty MAF or flow meter sensor.
The MAF sensor (Mass Air Flow Meter Sensor) is in charge of detecting how much air (in mass, not volume) is coming in to the engine, so the ECM computer can calculate the optimum amount of fuel to be injected in the combustion chamber.
Sometimes, these air flow sensors get contaminated by lots of microscopic debris that scape the air filter of the vehicle and accumulate over time on its sensing parts. Backfires are other contributor of excess carbon on these elements, specially because the elements are already at the other side of the air filter of the vehicle, making it to be exposed. The resulting effect is that the MAF flow meter sensor gets less “sensible” and detects less air than it is actually entering the engine. The reaction of the ECM computer will be to variably inject fuel while attempting to keep the air fuel balance at the stoichiometric rate (close to 14:7), taking as reference the false reading of the MAF flow meter sensor, producing that way the hesitation.
If your car engine, besides the hesitation, is also producing engine knocking or engine pinging at high loads, like when going uphill, it is also caused by the too-lean condition described in the above paragraph.
Before going to an auto parts store or to a mechanic to fix the problem, you should try fixing it your self. If the problem is a dirty MAF flow meter sensor, the solution is to clean it, plain and simple. That will save you some money. Otherwise, your mechanic will charge you for cleaning it for you. Some others will replace the part instead, when most of the times it is not damaged.
Here are some guidelines to do it by your self. You will be glad you saved money and learned how to do this, so you will be prepared for the next time it happens to you, your family or friends.
You will need a #2 Phillips screwdriver (shown in the picture below) for removing the two screws that hold the MAF in place and will also need a spray can of a special MAF sensor cleaning product. This cleaning product is designed to clean without harming, the sensitive MAF internal parts. The brand “CRC” is an excellent option and it is not expensive at all, the “Mass Air Flow Sensor Cleaner“:
Now, you will need to locate the MAF sensor in your Toyota. It is very accessible and no mechanical experience is needed to do this. In the picture below, the location of the MAF flow meter sensor of the 2004, 2005, 2006 and 2007 Corolla is shown. You will find it inside the engine compartment, looking at the air intake assembly, it is behind the vehicle’s battery. It is attached in place by two #2 Phillips screws. Take the screws out with a #2 Phillips screwdriver.
After removing the screws and putting them in a safe place, now pull out the MAF sensor. Sometimes it could feel a little bit attached, but if both screws are removed, it will come out. Just pull it gently.
In the next picture, it is shown the MAF sensor already pulled out. Now you must disconnect the attached wiring harness by pushing a plastic clip located in the plug itself, while pulling away the plug at the same time. It will easily come out.
With the MAF sensor already out, put it in a table over a paper towel or a cloth and spray directly to the connector harness with the CRC cleaner, to clean the contacts from debris and dust. Just spray it with full force for a couple of seconds. You should wear eye protection on this or be very careful so the bouncing spray does not get into your eyes. Do this in a well ventilated area.
Now, spray with full force inside the MAF sensor openings for a couple of seconds on each opening. Avoid the straw of the spray can from touching any of the internals of the MAF sensor. After spraying, repeat it one more time and when finished, put the MAF sensor upside down, so the excess liquid drips out. Allow enough time for the MAF sensor to be completely dry before reinstalling it in your vehicle. The CRC chemical is designed to dry almost instantly and it does, but spraying for a few seconds over the surface and internals of the MAF sensor, it will considerably lower the temperature, causing water condensation from the environment moisture and that water will take more time to evaporate than the CRC cleaner’s chemical. A good trick is if the engine is warm by chance (you drove the car before doing this job), just put the MAF sensor on top of the plastic cover of the engine for at least 15 minutes and the heat will dry it completely.
IMPORTANT! Please only use the chemical (spray) described here or one that was designed similar purposes, which (1) will not harm polymers (plastics), (2) will not harm electrical connections (not acidic) and (3) most important, will not leave any residue when it vaporizes. Cleaners that contain lubricants, like WD-40 for example, may not be used for this job. Any residue left inside the MAF sensor will damage the part. Remember that this job is about removing contaminants, not replacing them with some other substance 🙂
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