Old Avensis Mystery
Discussion
Hello everyone, looking for some advice please on a Mk1 Avensis I bought recently. It's a 2001 plate 2nd phase model having the VVT-i engine and OBDII capacity.
For a 20-year-old car it's not in overly bad shape, usual battle scars on bumper and paintwork etc, and it didn't start up initially. This was sorted by the dealer popping in a new battery and of course with this was able to hear it start and run from cold which is always good. Also survived a 100 mile trip home without missing a beat too.
However upon turning the engine off it took a couple of goes to start, but when running stayed running and drove well. I put this down to the previous owner not having had it serviced for almost 20,000 miles; suspecting the air filter and spark plugs and the like. Treated the car to a major service, drove noticeably better although still took generally a couple of cranks before starting. Would start on first try occasionally.
Thinking the lazy starting was due to either an on-its-way-out starter motor, or simply the battery terminals needing a clean, a week or so post-service me and a more mechanically-minded mate cleaned the terminals, after which the car started first time, and proceeded to drive it up a pair of ramps to locate the starter motor. We needn't have done this to find it in the end but anyway... Starter motor and its connections looked alright and had voltage to it.
After this a new problem presented itself, the car starts but now the engine stalls with revs going skew-whiff up to 3000rpm on its own before it dies. Sometimes it's not as sporadic but still stalls. Cue some online research leading to us testing voltage to the throttle position sensor and its connectors - all good there spark-wise I believe. Reference voltage read 3.5v - is this okay for this model? - as I understand it between 3.5v and 5v is sufficient - alongside commensurate readings with gradually pressing the accelerator pedal down.
From what I gather it shouldn't be the crankshaft position sensor as the RPMs are registering in sync?
Next we read two DTC codes on a scanner - P0100 Mass Air Flow Circuit and P0110 Intake Air Temperature Circuit - which led us to disconnecting the mass air flow sensor - now the engine runs, albeit roughly - though without stalling. So I purchase a new MAF sensor which arrives yesterday, we install it and alas, the same issue, engine starts and then stalls again. Upon disconnecting the new sensor, car runs as before without stalling.
It only has 106,000 on the clock so it's not an ex-taxi.
Anyone know or have an inkling as to what the issue or issues could be?
Based on my limited knowledge maybe:
1. With taking off and putting back on intake manifold to inspect starter motor, we've caused or exacerbated a vacuum leak?
2. With car being at incline on ramps, worsening a fuel feed issue?
3. Idle re-learn procedure needed?
4. Manifold Absolute Pressure sensor?
5. Electrical Gremlins?
Regards and thanks in advance.
For a 20-year-old car it's not in overly bad shape, usual battle scars on bumper and paintwork etc, and it didn't start up initially. This was sorted by the dealer popping in a new battery and of course with this was able to hear it start and run from cold which is always good. Also survived a 100 mile trip home without missing a beat too.
However upon turning the engine off it took a couple of goes to start, but when running stayed running and drove well. I put this down to the previous owner not having had it serviced for almost 20,000 miles; suspecting the air filter and spark plugs and the like. Treated the car to a major service, drove noticeably better although still took generally a couple of cranks before starting. Would start on first try occasionally.
Thinking the lazy starting was due to either an on-its-way-out starter motor, or simply the battery terminals needing a clean, a week or so post-service me and a more mechanically-minded mate cleaned the terminals, after which the car started first time, and proceeded to drive it up a pair of ramps to locate the starter motor. We needn't have done this to find it in the end but anyway... Starter motor and its connections looked alright and had voltage to it.
After this a new problem presented itself, the car starts but now the engine stalls with revs going skew-whiff up to 3000rpm on its own before it dies. Sometimes it's not as sporadic but still stalls. Cue some online research leading to us testing voltage to the throttle position sensor and its connectors - all good there spark-wise I believe. Reference voltage read 3.5v - is this okay for this model? - as I understand it between 3.5v and 5v is sufficient - alongside commensurate readings with gradually pressing the accelerator pedal down.
From what I gather it shouldn't be the crankshaft position sensor as the RPMs are registering in sync?
Next we read two DTC codes on a scanner - P0100 Mass Air Flow Circuit and P0110 Intake Air Temperature Circuit - which led us to disconnecting the mass air flow sensor - now the engine runs, albeit roughly - though without stalling. So I purchase a new MAF sensor which arrives yesterday, we install it and alas, the same issue, engine starts and then stalls again. Upon disconnecting the new sensor, car runs as before without stalling.
It only has 106,000 on the clock so it's not an ex-taxi.
Anyone know or have an inkling as to what the issue or issues could be?
Based on my limited knowledge maybe:
1. With taking off and putting back on intake manifold to inspect starter motor, we've caused or exacerbated a vacuum leak?
2. With car being at incline on ramps, worsening a fuel feed issue?
3. Idle re-learn procedure needed?
4. Manifold Absolute Pressure sensor?
5. Electrical Gremlins?
Regards and thanks in advance.
My money would be on a vacuum leak with a secondary diagnosis of electrical gremlins. I read your post twice and nowhere did you explain about messing with the intake manifold, that I could see? I would check that and all vacuum hoses carefully. I did a search on both those codes and one hit was a PCV valve not connected that threw both of them
Connecting the MAF might enable the engine to start messing with the air fuel mixture to try and compensate for a lean mix an cause problems leading to a stall. Without that, it can limp on. It's a theory!
Those codes are symptoms, not necessarily causes. Can you see fuel trim on your scan tool? It would be interesting to see short term fuel trim as you connect and disconnect the MAF sensor
How about the wiring for the MAF? Check that carefully too.
As the owner of a fuel pressure gunge, if it were me, I would pull that out too to see if it told me anything.
Connecting the MAF might enable the engine to start messing with the air fuel mixture to try and compensate for a lean mix an cause problems leading to a stall. Without that, it can limp on. It's a theory!
Those codes are symptoms, not necessarily causes. Can you see fuel trim on your scan tool? It would be interesting to see short term fuel trim as you connect and disconnect the MAF sensor
How about the wiring for the MAF? Check that carefully too.
As the owner of a fuel pressure gunge, if it were me, I would pull that out too to see if it told me anything.
Edited by Stigproducts on Wednesday 18th August 06:30
Morning Stigproducts,
Thank you for your helpful reply, it's given me hope and scope.
Yes we removed the intake manifold to access the starter motor, perhaps a new gasket is in order?
Interesting re: PCV valve, I'll look into this.
Have to admit fuel trim is a new one on me! Will put my head together with friend sure we'll be able to crack it if looks like that could be the culprit. My scanner is only a basic one linked to an app for readings.
Haven't tested MAF connection yet, will do that, check PCV and if need be will buy a better scanner, vacuum gauge and fuel pressure gauge.
Good point on codes being symptoms.
Thanks again.
Thank you for your helpful reply, it's given me hope and scope.
Yes we removed the intake manifold to access the starter motor, perhaps a new gasket is in order?
Interesting re: PCV valve, I'll look into this.
Have to admit fuel trim is a new one on me! Will put my head together with friend sure we'll be able to crack it if looks like that could be the culprit. My scanner is only a basic one linked to an app for readings.
Haven't tested MAF connection yet, will do that, check PCV and if need be will buy a better scanner, vacuum gauge and fuel pressure gauge.
Good point on codes being symptoms.
Thanks again.
Update...
After deciding to check PCV valve first - which looks oily but still rattled - we decided to take the intake manifold off and have a look for anything visible causing a vacuum leak before I bought any kit... We must have knocked a loose hose off its place first time around! Thankfully stays running and well now, albeit with the hard start issue returned.
Scootersp - Thanks for your reply. Ignition switch was something that a search returned when I first looked into initial problem online, have a thread saved on how to replace if needed. Does sound like that's the culprit, fuel filter presumably could do with a change but seeing as it runs just fine once it gets going it's doing its job.
After deciding to check PCV valve first - which looks oily but still rattled - we decided to take the intake manifold off and have a look for anything visible causing a vacuum leak before I bought any kit... We must have knocked a loose hose off its place first time around! Thankfully stays running and well now, albeit with the hard start issue returned.
Scootersp - Thanks for your reply. Ignition switch was something that a search returned when I first looked into initial problem online, have a thread saved on how to replace if needed. Does sound like that's the culprit, fuel filter presumably could do with a change but seeing as it runs just fine once it gets going it's doing its job.
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