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Matt, Mechanical Engineer
Category: Toyota
Satisfied Customers: 23190
Experience:  BEng hons Mech engineering, in auto industry 22 years
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rav4 2003, 2.0. car wants to cut out when driving also hesitates,

Customer Question

rav4 2003, 2.0. car wants to cut out when driving also hesitates, when ticking over the revs will suddenly drop right down and then go uo to about 1200 then settle ,all these problem are intermittent but are getting worse, the engine management light is not on but it flickers when these things happen. i have changed the mass air flow sensor,and took off the throttle boby and cleaned it but problems still there .thanks
Submitted: 4 years ago.
Category: Toyota
Expert:  Matt replied 4 years ago.


This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.

This leads them to be quite intermittent in the case of mild leaks

its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue

On no account touch the sensor wires with anything physical as they are extremely fragile

Customer: replied 4 years ago.

hi,there are no vacuum leaks/the fuel pressure is okay it has a new air mass flow sensor i have fitted new idle control valve,two mechanics dont know where to go with it they have tried all your previous suggestions, wondering if there was anything else to check thanks

Expert:  Matt replied 4 years ago.
Hello John

This could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;
Airflow meter
Crank position sensor
O2 sensor
Throttle position sensor

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.
Customer: replied 4 years ago.

car still doing the problems but got worse over new year when couldnt even drive it as it was kangerooing and like a massive flat spot also i noticed that the mpg /average fuel consumptions readings on the radio screen were changing erreticly ie,going 10.4 to4.8 to34.8 example .i have now put it in a garage the ca rstalls all the time they have changed cranksaft sensor but to no avail .they are a bosch diagnostic centre and have all the relevant equipment but cannot find the fault they have even phoned up toyota technical but still cant get to bottomof it. i was wondering if the consumption readings have anything to do with it. thanks

Expert:  Matt replied 4 years ago.
Hello John

sorry to hear you're still having issues with this

a fluctuating consumption reading could point to the injectors being shut down and then lighting off again so either the ECU power is being interuppted or the crank signal to the ECU is being interuppted

I'd also check the tightness and condition of the small earth connections onto the engine - the ones that terminate in small ring terminals as these are the ones for the ECU injector and ignition drivers

Expert:  Matt replied 4 years ago.

do you still need help with this?