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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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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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