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Discussion Starter · #1 ·
Hello all,
As I turned on my 2001 mr2 with 42k miles I was greeted with a check engine light.
Using a scanner there was 4 codes: (P0300,P0301,P0100,P0110)

P0300- Random Multiple Cylinder Misfire Detected

P0301- Cylinder 1 Misfire Detected

P0100- Mass or Volume AirFlow Circuit

P0110- Intake Air Temperature Circuit

Worth noting that I recently put in a new Mass Air Flow sensor in so i found it weird that I got a code for that.
Wondering if they are all connected and if someone can help since I don’t know where to start. Thank you in advance kind spyders.
 

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Yeah P0100 and P0110 indicate that the MAF sensor is not plugged in, or it's dead, or its wiring is cut - in other words the ECU is not even detecting its presence (or the temperature sensor which is built in to the MAF sensor).

Misfires will result.

It's all connected.
 

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Discussion Starter · #6 · (Edited)
Thought I’d Update: installed a new maf sensor and pcv with hose, did a vacuum leak test with a diy smoke machine, replaced that leaking hose and running a bit better although still have the issue where when I turn on the car about 5 seconds later the rpm’s drop to hard shaking, ordered a new downstream 02 sensor since I haven’t replaced it since I got the car but have replaced the 2 upstream ones on my gutted precats. Have a throttle positioning sensor saved in my cart just incase the downstream O2 sensor doesn’t fix my idling as well as a new idle air control valve. compression test is after that.

edit: I also changed spark plugs and ignition coils along with this update
 

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On warmed engine, a OBDII sould read 11% of throttle at idle. If your OBDII read same, don't replace the throttle sensor. Still on warmed engine, turn the A/C ON or lights ON. If you see the rpm going and stay higher, then the IACV can be faulty. Good IACV = rpm should go back to 800rpm. Very low idle (especialy on cold start) and shaking idle can be a faulty/failed coil on cylinder N°1 (chain tentionner side).
 

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Discussion Starter · #8 ·
On warmed engine, a OBDII sould read 11% of throttle at idle. If your OBDII read same, don't replace the throttle sensor. Still on warmed engine, turn the A/C ON or lights ON. If you see the rpm going and stay higher, then the IACV can be faulty. Good IACV = rpm should go back to 800rpm. Very low idle (especialy on cold start) and shaking idle can be a faulty/failed coil on cylinder N°1 (chain tentionner side).
thank you for your reply kind stranger, I forgot to add that I did put new spark plugs and ignition coils about 2 weeks ago, will do the iac valve check
 

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Discussion Starter · #9 ·
Update, replaced O2 downstream sensor and that did nothing haha iac valve proves to work just fine. Just for reference at cold start idle rpm’s look like this:

Sky Cloud Font Gauge Gas


once the engine is warmed up rpm’s look like this (normal?) :

Gauge Automotive lighting Measuring instrument Hygrometer Gas
 

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On cold start the ecu reads the Engine Coolant Temp sensor and applies cold start fuel enrichment.

If the ECT sensor is faulty, the ECU uses a fail-safe temperature and the fuel mix may not be suitable for cold start.

If the engine idles poorly cold but idles ok when warmed up this could point to a ECTS issue.

Two ways to check this:

1. The CEL is on and you have a code for ECT sensor circuit high or low. But beware of the infamous P0125 - this one has nothing to do with coolant temp.

2. Scantool live data reads an incorrect value for the ECT.
 

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Discussion Starter · #13 ·
On cold start the ecu reads the Engine Coolant Temp sensor and applies cold start fuel enrichment.

If the ECT sensor is faulty, the ECU uses a fail-safe temperature and the fuel mix may not be suitable for cold start.

If the engine idles poorly cold but idles ok when warmed up this could point to a ECTS issue.

Two ways to check this:

1. The CEL is on and you have a code for ECT sensor circuit high or low. But beware of the infamous P0125 - this one has nothing to do with coolant temp.

2. Scantool live data reads an incorrect value for the ECT.
That makes sense thank you. I just purchased one and will replace, will update with the findings
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Discussion Starter · #17 · (Edited)
Hi, unfortunately not, I’m working on the issue here and there. My last work on the car was buying and installing the temp sensor which didn’t do much toward the main issue. (The old sensor did look rough though.)

Hand Finger Household hardware Spark plug Wood


My next step is a compression test
Did that new MAF from Denso fix the issue? I got the exact same problem.
 

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Hello all,
As I turned on my 2001 mr2 with 42k miles I was greeted with a check engine light.
Using a scanner there was 4 codes: (P0300,P0301,P0100,P0110)

P0300- Random Multiple Cylinder Misfire Detected

P0301- Cylinder 1 Misfire Detected

P0100- Mass or Volume AirFlow Circuit

P0110- Intake Air Temperature Circuit

Worth noting that I recently put in a new Mass Air Flow sensor in so i found it weird that I got a code for that.
Wondering if they are all connected and if someone can help since I don’t know where to start. Thank you in advance kind spyders.
With both P0100 and P0110 not being fixed by the new sensors, it would seem very likely that you have a wiring issue. Start with figuring out where both of these circuits are grounded and clean up the ground connections.
 
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