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justinsbg, ASE Certified Technician
Category: Honda
Satisfied Customers: 977
Experience:  ASE certified in Brakes, Electrical, HVAC, and Engine Performance. Currently a lead diagnostic Technician.
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Have a 2004 honda accord lx 4cyl. Just replaced iac today.

Customer Question

Have a 2004 honda accord lx 4cyl. Just replaced iac today. After replaced it, the engine idles at 2000 rpm cold and normal operating temperature. Does not surge. I checked for vacuum leaks and none were found. Tps voltage was good. When I disconnect MAP sensor, idle goes to 700 rpm normal. Back probed leads for MAP and have 5 volts for power, a good ground, and center probe is 3.7 volts key on engine off. That same center probe is 0.8 volts with car running and idling at 2000 rpm. These readings were the same with the MAP sensor connected and disconnected. Why does rpm go to normal with a disconnected MAP sensor? Why am I still getting the same voltage with the MAP sensor unplugged? What is the normal voltage for the center lead of the MAP sensor with key on and car not running, plugged in as well as unplugged? With MAP sensor disconnected, i drove it and it stalled out when I stopped. I disconnected the egr valve with the car running and it had no impact on the rpms. When I unplugged the iac with car running the rpms were fluctuating between 1500 to 2000 rpm. When I plugged it back in it stayed solid at 2000 rpm. Drove car with everything hooked up, after drive I put it in park and rpms shot to 2700. I immediately cut it off and started it back up with rpms going to 2000.
Submitted: 1 year ago.
Category: Honda
Expert:  justinsbg replied 1 year ago.


My name is ***** ***** I would be happy to help. Do I gather in your question that this issue didn't start until the IAC was replaced?

Customer: replied 1 year ago.
I had a low, erratic idle prior to replacing the iac. The high idle and other issues mentioned were after the iac replacement.
Expert:  justinsbg replied 1 year ago.
Reminder, I have not been paid at this point and won't be until I receive a positive rating from you. At that point I will receive a portion of what you've already paid Just AnswerI suspect that there is air trapped in the cooling system. When you replaced the IAC valve the system should have been properly bled. This is critical to do because it creates issues such as this if it isn't done. You should have the vehicle parked on an incline (front end pointed towards the sky), or jack the front end of the vehicle up. Remove the radiator cap (when cold) and start the engine. Turn the heater on high speed inside. Let the engine idle until the cooling fans cycle. Turn the inside fan off and let the cooling fans cycle a few more times. This is messy because coolant will come out of the radiator so you can buy a spill free funnel. I'm pretty sure you can buy these at auto parts stores such as advance. This is how you properly bleed the system. Otherwise the air will prevent sensors accurately reading the temperature which will result in the PCM thinking the engine is always cold resulting in the high idle. If you have any questions about this just let me know.You can go ahead and rate me positively. Don't worry, there aren't additional charges for posting to this thread after you rate so we can keep chatting. Thanks!
Customer: replied 1 year ago.
We performed the cooling system venting for 4 cycles but that had zero impact on the rpms. We checked the throttle and cruise cables and they were fine. What about the questions u had regarding the map sensor yesterday? Again today we disconnected the map sensor and it went to normal idle. Were the voltages I gave you normal? It is still idling 2000 steady rpm.
Expert:  justinsbg replied 1 year ago.

So sorry for the delay. I have been incredibly busy and not able to work on just answer the past few days. I am back and ready to help out if still needed. I will be going over the details here ans responding back shortly. Thanks so much for your patience

Expert:  justinsbg replied 1 year ago.

Would you happen to have access to a scanner where you can view some live engine data?

Customer: replied 1 year ago.
I am still having the issue. I know someone with a scanner that does live data. I dont know how basic it is though. Are there certain fields or readings in particular that you are looking for?
Customer: replied 1 year ago.
I am also curious about what your thoughts are on the MAP sensor info and readings that I sent to you.
Expert:  justinsbg replied 1 year ago.

Typical MAP voltage is around 2.8 KEY ON ENGINE OFF. The map and baro sensor readings are usually identical during KEY ON ENGINE OFF. I am not familiar with what the voltage is for the input when the MAP is unplugged because I have never had a reason to check this, and I don't think this information will help. The MAP voltage while the engine is running looks normal so there is probably not an issue with the MAP sensor. Plus, it would not make the engine idle high. It could for a vehicle equipped with an electronic throttle, but this throttle is cable driven.

I want to know what the TP sensor is reading in volts during KEY ON ENGINE OFF as well as the voltage reading when the engine is running

Customer: replied 1 year ago.
TPS .50 volts idle and 4.5 volts full throttle with key turn to run with engine not running. With engine running, .51 volts DC idle.
Expert:  justinsbg replied 1 year ago.

that's normal. are the baro sensor and map sensor reading the same with KEY ON ENGINE OFF?

Customer: replied 1 year ago.
The only info I have on the map sensor reading is what I gave you earlier. That was.... Backprobed leads for MAP and have 5 volts for power, a good ground, and center probe is 3.7 volts key on engine off. That same center probe is 0.8 volts with car running and idling at 2000 rpm. These readings were the same with the MAP sensor connected and disconnected. What is a baro sensor?
Expert:  justinsbg replied 12 months ago.

Can you tell me what the coolant temp sensor is reading after the car has been running for about 10 minutes?

Customer: replied 12 months ago.
I was googling and looking on you tube to find a location on this sensor. It was mentioned there are two of them. One they showed in the area of the radiator and the other closer to the back of the engine. Where is the sensor that you are referencing located?