Intermittent stumble

[mechtech2]

Originally Posted By: 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.


The symptoms were no codes, multiple cyl codes, and specific cyl codes. Not exclusively specific cyl codes.
And there may be multiple problems, not just one item.

 

[firefighter]

Originally Posted By: mechtech2
Originally Posted By: 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.


The symptoms were no codes, multiple cyl codes, and specific cyl codes. Not exclusively specific cyl codes.
And there may be multiple problems, not just one item.


Yes it just did not log codes at first. I have ford trucks come in that are missing plain as day and will not turn a light on, you have to look at mode 6 data to determine a missfire. The car just didn't turn the light on right away. Seems like a simple ignition miss, I could be wrong though. If a IAC/ECT sensor was that far off it probably would have set a code, or there would be a problem all the time. If those sensors fail and don't set codes they gernerally shift there range and feed wrong temps so the problem would be all the time not intermitant. Now if there was a poor connection at a sensor that would be a differant story, but that is doubtful. We have logged two codes for specific cylinders lets start there, just my two cents.

 

[Techniker]

Toyotas are much more sensitive than Fords. Toyota typically has very low tolerances for throwing an engine code. Fords on the other hand...I generally wonder if they even have a computer in them.

I agree though, it is something to look into, but it's not where my bet is.

 

[firefighter]

Originally Posted By: Techniker
Toyotas are much more sensitive than Fords. Toyota typically has very low tolerances for throwing an engine code. Fords on the other hand...I generally wonder if they even have a computer in them.

I agree though, it is something to look into, but it's not where my bet is.


This is all good dialog, where do you lay your bet. I hope the original poster will fix the repair once it is known. It is tough to fix through the net. If it is a lean problem I would lean to the maf being dirty. I do not think a fuel injection issue, as there were codes for two cylinders. Injectors do not clean themselves up and then get dirty again to cause an intermitant problem. I am going to stick with ignitoin. I hope we get a fix

 

[ChiTDI]

I'm still diagnosing and logging uneventful miles. For a week I've started up cold and logged the time to reach operating coolant temperature and matched the Intake temp to it. Cold reads show both temps within a degree or two of each other. Coolant temps rise steadily and takes anywhere from two to four miles to approach 180 degrees, depending on driving demands and ambient temp. IAT readings are much slower to change but do so steadily. Scangauge not dash gauge.
I cleaned the ECT connection as well as the MAF connection today and will watch for any change. Then I'll clean the MAF with dedicated cleaner. The IAT connection is something I'm not sure of. It is not in the parts locator in the Factory service manual, but there appears to be a gizmo on the outside of the airbox that has wires from it to the MAF harness.
I'll stay on this and post results and repair. THANK YOU all for your help.

 

[ChiTDI]

Has been almost a month with no reoccurrence of any symptoms.
I cleaned the MAF connector and the coolant temp sensor connector with DeOxit D5 and got a little sizzle on one of the connector prongs. That may have been it. Hopefully anyway. No codes etc, and flawless performance cold start through warmup to fully warmed and operational.
Thanks to all who stepped in and helped me.