Intermittent stumble

[ChiTDI]

Wife has been complaining of rare instances of the engine stumbling and sometimes dying in an '02 Avalon w/133k mi.
Scanned the engine and found no codes. Finally yesterday I drove it and felt the stumble, feathered the accelerator and was able to get a CEL. Codes came up P0300 (multiple misfire) and P0304 and P0306 (misfire cylinder specific). Cleared the codes and drove it for 50 miles with no issues. The engine runs really well normally, starts flawlessly, and idles right. Seems like the stumbling occurs 2 to 3 miles from dead cold, and doesn't occur once the engine is fully warmed.
I'm thinking of a coil or plug shorting just as the open/closed loop voltage changes. Any thoughts?

 

[pcoxe]

Could be a fuel injector not firing as well. The controller is reporting the cylinder produced no power when it was supposed to.

 

[Eddie]

You state 2-3 miles after cold start. That suggests to me that the computer has shut down the cold running mixture. Engine could be going lean untill fully warm. First thing I would try is a good FUEL SYSTEM CLEANER like TECHRON or Red Line. Use a system cleaner instead of the weaker injector cleaner. This presemes you have done the factory prescribed tune-up etc. Ed

 

[mechtech2]

A good in tank cleaner is great maintenance 1-2 times a year.

You may have a small vacuum leak, or a coolant sensor for the computer [not necessarily the gauge] is a bit out of whack.

Dedicated spray MAF cleaner is a great idea, and cheap and easy to use. Good to do at this point no matter if it is the root problem or not.
Also, a manual cleaning of the throttle body bore and plate with solvent and a rag is always good.
Ignition is not my first guess, because it is isolated temperature related.

 

[Techniker]

I agree that it sounds like an EFI problem. I think Eddie is on it with the engine running too lean at low engine temperature. I would also try the Techron concentrate and follow it up with a can of B12 afterward.

Just out of curiosity, and I'm sure it's fine, how is your coolant level? Another alternative (and is part of the EFI sensing system) is that you have a temperature sensor that is on the fritz. How often does your wife says this happens?

-Techniker

 

[ChiTDI]

Geez the coolant sensor idea really makes sense. Computer mistakenly thinks the car is warmed and leans the fuel to the point of stumble. No codes.
I did check the coolant level, as Techniker said, and it was fine.
You are right about the MAF cleaner, Mechtech, I've never done it and it's been over a year for the intake cleaning. Good time to do both.
Is the coolant sensor "check by replacement" or can I get an ohm reading to determine life or death?

Thanks again to all.

 

[Techniker]

Originally Posted By: ChiTDI
Geez the coolant sensor idea really makes sense. Computer mistakenly thinks the car is warmed and leans the fuel to the point of stumble. No codes.
I did check the coolant level, as Techniker said, and it was fine.
You are right about the MAF cleaner, Mechtech, I've never done it and it's been over a year for the intake cleaning. Good time to do both.
Is the coolant sensor "check by replacement" or can I get an ohm reading to determine life or death?

Thanks again to all.


Coolant sensors can be checked with an ohmeter as they are typically mere rheostats that change resistance with a change in temperature. Unfortunately, as with a lot of electrical problems, the problem may be intermittent and extremely difficult to reproduce. I would price it at Advanced Auto Parts and Autozone, you may want to replace it anyway if it's cheap enough. They're usually pretty simple sensors. Something else to consider- check the wiring harness, cracks in the heat shielding and insulation can alter the resistance of the wire and also throw the code.

-Techniker

 

[demarpaint]

It could be in need of a FI cleaning, so using a good cleaner is worth a try, and is cheap. The Coolant Temp Sensor, or Air Temp Sensor could be causing the problem as well. Both sensors are telling the ECM how hot or cold it is and the ECM is adjusting for it. Fed the wrong data the ECM doesn't know what to do.

 

[Techniker]

Originally Posted By: demarpaint
It could be in need of a FI cleaning, so using a good cleaner is worth a try, and is cheap. The Coolant Temp Sensor, or Air Temp Sensor could be causing the problem as well. Both sensors are telling the ECM how hot or cold it is and the ECM is adjusting for it. Fed the wrong data the ECM doesn't know what to do.


Agreed. When in doubt, always do the cheapest and most likely choice first. I would run it around with first a cleaning of Techron concentrate in the tank. When that tank runs out, run it with B12 Chemtool in it. Between the two, you should be able to at least rule out a dirty FI. No clicking sounds either, correct?

 

[firefighter]

When was the last time plugs were done on this car??? I am leaning towards ignition. The best way to get a car to miss is up a hill, torque convertor locked, and just squeeze the throttle lightly until the TC is ready to unlock. you want lower speeds not much rpm. that puts the most load on the ignition system. You just may not have been driving like your wife does, and that is why it does it cold for you.

As for the dying I would wonder how clean the throttle plates are.

A little maintance history would help

Best of luck

 

[ChiTDI]

Originally Posted By: Techniker
Originally Posted By: demarpaint
It could be in need of a FI cleaning, so using a good cleaner is worth a try, and is cheap. The Coolant Temp Sensor, or Air Temp Sensor could be causing the problem as well. Both sensors are telling the ECM how hot or cold it is and the ECM is adjusting for it. Fed the wrong data the ECM doesn't know what to do.


Agreed. When in doubt, always do the cheapest and most likely choice first. I would run it around with first a cleaning of Techron concentrate in the tank. When that tank runs out, run it with B12 Chemtool in it. Between the two, you should be able to at least rule out a dirty FI. No clicking sounds either, correct?


Correct, no clicking sounds or stumbling under any situation when fully warmed.

Originally Posted By: firefighter
When was the last time plugs were done on this car??? I am leaning towards ignition. The best way to get a car to miss is up a hill, torque convertor locked, and just squeeze the throttle lightly until the TC is ready to unlock. you want lower speeds not much rpm. that puts the most load on the ignition system. You just may not have been driving like your wife does, and that is why it does it cold for you.

As for the dying I would wonder how clean the throttle plates are.

A little maintance history would help

Best of luck


Plugs were done at 105k, so almost 30k on them.
Throttle body was cleaned almost 18 months ago, and I put the engine through all kinds of driving situations when fully warmed and there is no performance problem that surfaces.


I'll run some fi cleaner and some B12, clean the MAF, and get an ohm reading on the coolant sensor. AIT sensor can be read with a DVM or is that "check by replacement"?

 

[Vikas]

Ask the ECM what it thinks the coolant temperature is. If it is not right, then you know that sensor needs to be replaced or wiring looked at. Similarly, you can ask ECM what the air intake temperature is. If it is not right, you can look at that sensor or its wiring.

Now you are going to wonder, how do I ask ECM? Knowing me, you should know that answer

- Vikas

 

[Techniker]

Originally Posted By: Vikas
Ask the ECM what it thinks the coolant temperature is. If it is not right, then you know that sensor needs to be replaced or wiring looked at. Similarly, you can ask ECM what the air intake temperature is. If it is not right, you can look at that sensor or its wiring.

Now you are going to wonder, how do I ask ECM? Knowing me, you should know that answer

- Vikas


You people with your expensive scan tools...

As previously stated, cleaning the idle air control is also something that could be a distinct possibility. The idle air control valve allows air to enter the intake manifold when the throttle plates are closed. This has been a known problem in the past with Toyotas, particularly because they pull the PCV gases through the IAC. In case you haven't done it before, when you pull off the bellows and open the throttle plate, you will see a keyhole shape in the bottom. Shoot some solvent cleaner in there and let it soak for a while. Just be sure not to completely fill the IAC with solvent or you're going to have a hard time starting her again. Be sure to keep us updated.

-Techniker

 

[Vikas]

But the scanner is relatively cheap. I paid under $100 for it when it was on sale and used the ubiquitous 20% off coupon.

Given that almost all of us who are driving cars with 6 figures on the odometer, we *will* run in to check engine light problems. Unfortunately, many will elect to randomly throw parts costing lot more than the price of a decent scanner.

- Vikas

 

[Techniker]

Wait, you bought a scanner with live stream for under $100? Is it one of the Ebay ones? I've toyed with the idea of buying one myself from there but I haven't heard any reviews from anyone so have held off. Tell me more!

I've never really had to buy one, since we have a high end scanner at work.

-Techniker

 

[mechtech2]

Coolant sensors vary in actual resistance/temperature, and even if they get more resistance or less as they heat up.
Sorry, I don't have the specs for your car.
But they do foul up and not throw a code, sometimes.
Remember, this is only one possibility.

There is often an intake air temp sensor, which may be MAF integrated or a separate sensor. Another guy to possibly go out!

Vacuum leaks have to be tediously checked manually. Yes, a big one is easy, but others need to trace each line and it's termination connection. Intake manifolding and piping is also critical.

 

[firefighter]

I am a little confused, why would a coolant or air temp sensor cause a mis fire on two cylinders only? I belive the P0300 set cause there was more than one miss or momentarily it could not identify the cylinders. but it seems we have a simple two cylinder miss at times. what plugs were put in when changed? and if the TP was cleaned about 18 months ago it may need it again, time can fly and that 18 months might be 4 years LOL.
Best of luck.

 

[ChiTDI]

Been driving the car around a lot and let her take it for the commute as well. No symptoms. It has been warm here though, so maybe tomorrow AM I'll get some history. Supposed to be down to 40.
I'll even hook up the scangauge and "talk with the animals".
Hit the library and got the specs for the coolant sensor but couldn't even find the AIT sensor in the parts locator schematic, even though it is listed as a part. Perhaps it will be evident when I inspect the MAF as mech mentioned.

Thanks again for your continuing support and thoughts.

 

[Scott_Tucker]

I would suspect it is an intermittent ignition misfire. Because you have replaced the plugs it is likely the boots that run from the coils to the plugs that are leaking. Coolant temp and air temp sensors won't cause an intermittent misfire. It's not likely a fuel injector problem unless you are using really bad gas. Dirty MAF is a possibility and cleaning it is easy enough.

 

[Vikas]

Originally Posted By: Techniker
Wait, you bought a scanner with live stream for under $100? Is it one of the Ebay ones? I've toyed with the idea of buying one myself from there but I haven't heard any reviews from anyone so have held off. Tell me more!

I've never really had to buy one, since we have a high end scanner at work.

-Techniker


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