Low fuel pressure may be culprit with hard starting Toyota

by Jim Kerr . May 13 2016

Question: I have a 2009 Toyota Corolla Sport with a 1.8 L engine, automatic transmission and air conditioning. It has 156,000 kilometres.

For the most part the car runs flawlessly. About a year ago I replaced the original battery after it went dead and cleaned the posts.

The car started fine and I shut it off after 30 seconds. The next morning my wife couldn’t start it when she left for work. It turned over fine, but didn’t seem to want to catch, but eventually did, there was some smoke and it ran rough at first, didn’t idle great, but after driving it for a while, all smoothed out and has been good ever since.

Then the other day, I pulled it out of the garage and shut it off. Later, it wouldn’t start. Sometimes the starter would even remain engaged until I put the key in the off position.

I cleaned the battery cables, put it on the battery charger for a couple of hours then tried to restart. Eventually it caught but didn’t run good, with some smoke and fumes and rough engine idle, almost stalling at intersections. After some driving, it smoothed out, and my wife says all is back to normal.

I changed the sparkplugs and cleaned around the throttle body opening using throttle body cleaner and a toothbrush.

I didn’t clean the MAF (mass air flow sensor), and my question is can I use throttle body cleaner on it too, or does it have to be the special MAF cleaner I saw at Canadian Tire? Will throttle body cleaner harm it?


Answer: Since the vehicle is running fine, I would not clean the MAF sensor. This sensor is very easy to damage because it uses fine wires to sense the mass of air flowing past it.

The sensor wires can be coated with an oily film over time from recirculated crankcase fumes and this can cause incorrect fuel delivery, but the computer will typically compensate by monitoring the oxygen sensors to adjust the air/fuel ratio. If you do attempt to clean the sensor, I would only use a spray type cleaner and do not touch the actual sensor wires. Alcohol works well as a cleaning agent to remove the oily film on the wires and that is one of the ingredients of Mass air flow cleaners. I have seen mass air flow cleaners cleaned using throttle body cleaner without harming it but they are a little more aggressive cleaners so use sparingly. Again, I wouldn’t clean it unless it is causing a problem.

I suspect that the starting problem with your car isn’t the mass airflow sensor. During cranking, the computer uses throttle position, coolant temperature and engine speed to calculate fuel delivery. The mass airflow sensor is used mainly after the engine starts. I have seen many vehicles with symptoms similar to yours and often it is caused by incorrect or no fuel pressure. The pump is probably sticking internally, possibly because of a tiny bit of dirt, and not supplying fuel pressure. Sometimes letting the vehicle sit will let the fuel slosh and move the debris. Charging the battery fully can also supply a little more power to the pump and it can clear the debris. The problem may clear itself and be fine, or it may start to act up more frequently. If it happens again, listen at the fuel tank filler to hear if the pump is running for a couple of seconds when the key is first turned on. If you can’t hear the pump, then you should check fuel pressure as a second check, but that is likely your problem.

Question: I am a new driver and want to look after my car carefully. My question is how often should I check the motor oil and tire pressure.

Answer: I would recommend checking oil level at every fuel fill up.

It only takes a minute. If you find the oil level dropping, then you may have a leak or the engine is consuming oil and you should check it more frequently. If the level remains constant, then you could likely check every second fuel fill.

Tire pressure should be checked once a month as a minimum and I always recommend checking tires before heading out on a longer trip. The tires should be cold when checked, as a tire that has been driven for even a short distance with low pressure will heat up and cause a false pressure reading.