Misfire after a stall?

[bobbe]

My car has been running smoothly as usual until the other day I stalled at a junction (rookie error, I know). I immediately got going again, but noticed that idle was now dropping below 1k rpm and was quite rough

The check engine light has since come on and my OBD reader says a misfire in all four cylinders (codes P0300, P0301, P0302, P0303, and P0304) as well as "System too Lean" on both Bank 1 and Bank 2 (codes P0174, P0171)

What is happening here? Am I looking at a new ignition coil pack? This started literally about two hours after I listed the car for sale, so I am loathe to spend too much money on it but this will need fixing

[normanh]

Theres 4 coil packs one for each cylinder, check each spark plug, the PO171/174 indicate weak mixture so check the air flow sensor. Its possible a weak mixture has damaged the plugs if the engine has run lean for too long.

Just a thought did it rain that day I had water in one plug years back and that caused a misfire.

Norman

[Gaz mr-s]

Remove the maf & check the o ring seal.  And clean the maf with an alcohol. The visible blob is a temperature sensor (I think), - the maf sensor is up inside the plastics. Protect the rubber o ring from the alcohol.

[Carolyn]

Almost certainly the Mass Airflow Sensor, follow Gaz's advice.  If no result, get a new MAF.

[Ardent]

I find it best to just gently remove the o ring altogether whilst doing the cleaning bit.

[mr2garageswindon]

Not crank sensor earth?

[fawtytoo]

Even if the error codes point to the MAF, why does the mis-fire only happen after the stall? Does something happen to the MAF when it stalled, or is it something else that makes it look like the MAF?

Could something have come loose when it stalled?

[Alex Knight]

My advice is to take note of all the existing codes.

Clear the codes, take it for a decent drive. See what (if any) codes come back.

[normanh]

Your misfire/lean mixture may have caused the stall, like everyone has said check check everything. Plugs MAF

Norman

[Dev]

It can be anything at this point. As Alex pointed out its best to reset and observe.
After that you need to see the data and a logging feature for ODB is invaluable as a process of elimination.
It is good to check the easy stuff before you wheel out the parts cannon which at this point is just guessing.
If it were me the first thing I would check is the electrical system by placing a load on it and then checking to see if one of the alternator diodes is burned out.

[jvanzyl]

I'm going to go with my old favourite the O2 sensors. They sensed your stall and took the opportunity to die. Regardless of the errors pointing to the MAF, I'm going to go with them being the culprits...

[Carolyn]

An air leak in the inlet system could be a cause also.  It's worth inspecting the vacuum hoses and the rubber inlet tube for holes/splits.

[bobbe]

Thanks for all advice - going to have a go at the MAF this afternoon and see if that makes a difference

If that doesn't fix it, I'm well past the point of wanting to faff around with this car or spend any time sorting it out - it's listed for sale because I wanted rid - so will probably just see about scrapping it

My advice is to take note of all the existing codes.

Clear the codes, take it for a decent drive. See what (if any) codes come back.

I should have said that I had already done this, and all the same codes showed up again

[bobbe]

Even if the error codes point to the MAF, why does the mis-fire only happen after the stall? Does something happen to the MAF when it stalled, or is it something else that makes it look like the MAF?

Could something have come loose when it stalled?

This is what I don't understand about it - it drove smoothly and normally without any hints of a problem until it stalled. Immediately after the stall it ran rough, then engine lights came on

[fawtytoo]

This is what I don't understand about it - it drove smoothly and normally without any hints of a problem until it stalled. Immediately after the stall it ran rough, then engine lights came on

Stalling can cause quite a jolt sometimes, so maybe this ...

Not crank sensor earth?

[normanh]

Bobbe you have had numerous words of wisdom offered as to possible solutions but have you actually tried any of them to date. Nearly all are so simple and really dont required a masters degree in motor mechanics to check. You just keep asking the same question sorry but you seem to be ignoring any possible solutions. Theres years of solid experience being offered here all be it various possible solutions based on individuals past experiences. You might think me a bit harsh in my comments but its the truth. I have been perfecting my skills for 50 plus years taught by my late father.

Norman

[bobbe]

Bobbe you have had numerous words of wisdom offered as to possible solutions but have you actually tried any of them to date. Nearly all are so simple and really dont required a masters degree in motor mechanics to check. You just keep asking the same question sorry but you seem to be ignoring any possible solutions. Theres years of solid experience being offered here all be it various possible solutions based on individuals past experiences. You might think me a bit harsh in my comments but its the truth. I have been perfecting my skills for 50 plus years taught by my late father.

Norman

I'm sorry, what? Those skills you've been perfecting for 50 plus years must not be reading skills - I asked the question once and then literally this morning said I would be trying the most commonly suggested solution (cleaning the maf) this afternoon

As it goes, cleaning the maf didn't work. I disconnected the battery (20 minutes or so) so the ECU would reset, cleaned the maf, cleared the fault codes, and the car runs just as rough as before - and the fault codes and EML came back. I've also tried the maf itself in another car for around 20 miles without any issues at all, so we can rule that out as needing replaced

@fawtytoo I will investigate the crank sensor earth tomorrow and see if that makes a difference

If that's not it, then at a stretch I might try swapping in some coil packs and plugs from my working car to rule those in or out as a source of the problem (though all four plugs were changed about 5k miles ago, so it seems unlikely that they would have all suddenly developed a problem at the same time). Past that point my enthusiasm for doing much more with this car is limited

[shnazzle]

Feeling the frustration. Been there for sure. Numerous times.

Applying some simple logic... whether it helps or not...code 300 usually will trigger 301-304, so that narrows down the codes.
Both banks going lean at the same time and all 4 cylinders misfiring is rather unlikely indeed.

It's something "wider" then.
The common culprits have been highlighted. MAF and crank for sensors, and one of the many intake hoses having come loose. Particularly the one into the blue  valve  above the airbox.

In order of how common...
- the crank sensor negative connection is known to corrode and form a bad connection. Misfires would 100% be a consequence of that. And subsequent stalling.

- in my (far too long) time on this forum I think I've seen 2 MAFs go. They get gunked up. But fail? Hardly. Putting this as #2 because it's very easy to clean, reset ECU and check whether it fixed it. You've done this, so just documenting for posterity

- intake hoses; these buggers are often popping off. Depending on where the car is kept they get quite brittle and tend to just drop off. This has happened to 3 of our 4 MR2s. If if falls off on the intake side, you have an unwanted source or unmetered air, making the car run lean, which can lead to misfires.


- o2 sensors: these bastards...these banes of all mr2 owner's lives. Their heating elements fail as a matter of sheer entertainment to Denso and Toyota. Just to mess with your head. But the o2 sensor itself? They age and slow down, but complete failure isn't massively common. And if they do, the symptoms are localised.


In the above is my order of checking. The crank sensor unfortunately being a bit of a pain to get to, but not silly difficult.

I do hope you get to the bottom of it. If only to satisfy my curiosity, but mostly so that you can maximise what you get for the car...or hell...keep it.

[Carolyn]

My money is on an intake hose.

[bobbe]

Feeling the frustration. Been there for sure. Numerous times.

Applying some simple logic... whether it helps or not...code 300 usually will trigger 301-304, so that narrows down the codes.
Both banks going lean at the same time and all 4 cylinders misfiring is rather unlikely indeed.

It's something "wider" then.
The common culprits have been highlighted. MAF and crank for sensors, and one of the many intake hoses having come loose. Particularly the one into the blue  valve  above the airbox.

In order of how common...
- the crank sensor negative connection is known to corrode and form a bad connection. Misfires would 100% be a consequence of that. And subsequent stalling.

- in my (far too long) time on this forum I think I've seen 2 MAFs go. They get gunked up. But fail? Hardly. Putting this as #2 because it's very easy to clean, reset ECU and check whether it fixed it. You've done this, so just documenting for posterity

- intake hoses; these buggers are often popping off. Depending on where the car is kept they get quite brittle and tend to just drop off. This has happened to 3 of our 4 MR2s. If if falls off on the intake side, you have an unwanted source or unmetered air, making the car run lean, which can lead to misfires.


- o2 sensors: these bastards...these banes of all mr2 owner's lives. Their heating elements fail as a matter of sheer entertainment to Denso and Toyota. Just to mess with your head. But the o2 sensor itself? They age and slow down, but complete failure isn't massively common. And if they do, the symptoms are localised.


In the above is my order of checking. The crank sensor unfortunately being a bit of a pain to get to, but not silly difficult.

I do hope you get to the bottom of it. If only to satisfy my curiosity, but mostly so that you can maximise what you get for the car...or hell...keep it.

Very helpful, thanks! I' will give the crank sensor a go and then look at the intake hoses

[bobbe]

The winner is....*drumroll*...Carolyn! Who correctly guessed an intake problem

I investigated the crank sensor earth (any excuse to have a poke about under a car) and found all as it should be, as you can just about see here:

You cannot view this attachment.

So I started looking around the intake and quickly found the culprit:

You cannot view this attachment.

It had come disconnected, but not obviously so unless you really looked at it

Hose reconnected, car runs smoothly as it should do with no codes

Thanks for all your help everyone!

[puma2]

  glad this ahs been sorted for you and good to see  help with information provided 

[shnazzle]

Knew it would be that blue valve...those damn hoses. You can see from the state of it what I meant

[Alex Knight]

@Carolyn well done you. Hats off.