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Discussion Starter #1
Hi All,

new here, couldnt find a solution with a search.

When warmed up, engine still idles about 1250. It makes driving sucky, truck wants to go, shifts weird and of course I have to apply heavy braking to stop.

I’ve just replaced my original motor on my 2007 Frontier with a 2015 used, 99k miles. Truck runs good, but it won’t go into low idle. I swapped the lower intake, and now the throttle body from original motor.

I just went through procedures to re-learn the low idle speed, but that didnt seem to change anything.

Truck does not throw any codes, except all four O2 sensors because I did a caralytic converter delete. I have not re-flashed ECU-could this have something to do with my problem?

Thanks for any replies!
 

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My idle speed relearn took weeks to take hold. I would give it more time.

Even with the cat delete, the upstream O2 sensors are still vital as they are used to set air fuel ratio. The downstream O2 sensors are used to assess cat efficiency. You should be receiving P0420 and P0430 codes. If you are getting codes for the upstream sensors, I would attend to them.
 

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I swapped a 2016 with 15,000 in my 07 this summer. When it first started it had a high idle, then after a few minutes settled in. How long did you run it for? Also when I did mind I swapped as much stuff over as I could from the 07 to the 16. Some of the electronics are different. (Including ECM). Also the throttle body I believe is slightly different.
 

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Generally the engine coolant temp sensor is used to give the computer feedback about where the engine is at in the warmup process. There is also an intake air temperature sensor that can adjust things based on the ambient air temp. The intake air temp sensor is built into the MAF.

The throttle body opening and idle speed is probably based on a few more parameters, but I think as far as temperature is concerned that's it.

Did you ensure all of the prerequisite conditions were met before preforming the idle air relearn procedure? Are you sure you got the sequence correct to perform the procedure? It looks a bit challengine not using a scan tool to initiate it.

322865
 

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Generally the engine coolant temp sensor is used to give the computer feedback about where the engine is at in the warmup process. There is also an intake air temperature sensor that can adjust things based on the ambient air temp. The intake air temp sensor is built into the MAF.

The throttle body opening and idle speed is probably based on a few more parameters, but I think as far as temperature is concerned that's it.

Did you ensure all of the prerequisite conditions were met before preforming the idle air relearn procedure? Are you sure you got the sequence correct to perform the procedure? It looks a bit challengine not using a scan tool to initiate it.

View attachment 322865
This is an interesting point. The OP said the engine was warm but revs were still high.

Is there a clock on the coolant temperature over-ride? Meaning, if the engine is running for 5 minutes or so, it enters closed loop regardless if the temperature sensor still reads low.
 

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This is an interesting point. The OP said the engine was warm but revs were still high.

Is there a clock on the coolant temperature over-ride? Meaning, if the engine is running for 5 minutes or so, it enters closed loop regardless if the temperature sensor still reads low.
I don't know about a time out, but I would think it would have a ton of problem entering (or maintaining) closed loop without a properly functioning engine coolant temp sensor. If there is no code for the sensor and it is bad, I would bet the computer is reading something from it, but that value is wrong.

If there is a time out, I would think it would activate the SES light and maintain open loop if closed loop is not possible in a reasonable amount of time. FSM indicates P1148 and P1168 will be triggered if the engine cannot enter closed loop.

OP might want to look at some live OBD-II data with the engine running at operating temp to make sure obvious things like coolant temp, etc. are being reported correctly.

An improperly functioning coolant temp sensor would probably prevent the idle air procedure from working. One of the prerequisites is coolant temp between 70 and 100 °C.

But like you mentioned if the OP removed all the cats he shouldn't be getting codes for the upstream O2 sensors. Faulty upstream O2 sensors would also prevent closed loop.

Listing the actual codes the truck is throwing would be helpful.
 

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Discussion Starter #11
Above posted are my trouble codes. I got all four codes before the engine swap, too, and I wasnt having idle problems with original motor.
 

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Discussion Starter #12
My idle speed relearn took weeks to take hold. I would give it more time.

Even with the cat delete, the upstream O2 sensors are still vital as they are used to set air fuel ratio. The downstream O2 sensors are used to assess cat efficiency. You should be receiving P0420 and P0430 codes. If you are getting codes for the upstream sensors, I would attend to them.
What do you mean, took weeks to hold? I’m wondering how can it learn to idle lower if it’s not at a low idle to learn?
 

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Looks like something is wrong with the O2 sensor heaters - all four of them. The sensors won't work if they aren't at the correct operating temperature. Truck can't operate in closed loop without them.

Check fuse 54 and the body grounds between the battery and fender, and the air box and fender (E9, E15, E24).
 

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Discussion Starter #14
Fuse was bad. Here are my codes now. It is still idling high, i’ll try relearning idle speed again.
322873
 

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Ok. I would clear the codes and see what comes back first. Truck needs to be driven for 10 minutes before you can do the relearn procedure, so do that and check for codes after driving.
 

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What do you mean, took weeks to hold? I’m wondering how can it learn to idle lower if it’s not at a low idle to learn?
I literally means it took weeks to relearn the right idle rpm. I started at 850 rpm and it took weeks to migrate down to 600-650 rpm.

It seems to me that your upstream sensors are toast. Since these did not come over with the replacement engine, they are suspect. Have you ever changed them out?
 

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Discussion Starter #18
What harness did you use?
What computer did you use?
What O2 sensors did you use?
i used everything you mentioned from the original truck. Only codes it is showing are P1148 and P1168 after resetting then driving around. I’m currently idling around 910. Question, should my absolute throttle position read 0 when at idle, or something like the 4.7% shown?
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Discussion Starter #19
I talked to someone who did the same swap. A 2005 pick up and a 2015 motor. He swapped over the oil pressure sensor and lower intake and had no other problems.
 

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The throttle body is drive-by-wire with no external idle air control valve so I would expect some throttle opening when the truck is idling. If the throttle body was completely closed the engine would stall.

So the O2 sensors codes all went away. That's progress. Have you tried the idle air relearn procedure again?

Maybe the closed loop codes will not allow the idle air relearn to happen. You might need to drive it a bit more, possibly at constant highway speed, for the truck to meet all the conditions to clear those codes. Does the emissions system readiness indicate complete or incomplete? If incomplete, which monitors specifically are incomplete?

The FSM lays out the specific driving patterns necessary to set readiness to complete. Refer to the section on "System Readiness Test". Some self diagnostics tests need to be preformed twice.
 
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