We got in 50 degrees temperatures here in north Texas this week. I noticed that in the morning engine starts off at rough idle (shaking) at 1250 rpm. In about 1 minute or 2 it gets to 1100 rpm idle and it runs perfect smooth from there on.
I recently changed both motor mounts, transmission mount, both rocker gaskets, all spark plugs, all plenum gaskets, both knock sensors, bypass hoses, almost all under plenum hoses, pcv, etc., and fuel filter.
I have added BG 44K to full tank twice within the last 5000 miles. What is the most likely cause of rough idle at 1250 rpm? Worst case scenario: One or two faulty injectors?
Rough idle
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maxnix
- Posts: 22627
- Joined: Mon Jul 22, 2002 8:11 pm
- Car: 1995 Infiniti Q45
1995 Infiniti Q45t
2000 Infiniti Q45
1250 rpm at idle?
Geez, I don't know, but neither of my 1995 Qs ever idle at that speed, even at cold starts below 40° F.
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
If it doesn't idle [in park/neutral] at 1200-1400 cold coolant crank you have a problem. The colder the coolant the higher the idle at least down to 20F ambient. The fast idle cam and control circuit are set [with extreme precision] at 32F, 77F, and off at just below 170F when the thermostat just begins to open.
Al this is critical to heat the precats and oxygen sensors FAST to enable the engine to go into closed loop operation as soon as possible
So that the oil is in the proper temperature range to LUBRICATE it is wise to not move the car until the coolant sensor reaches say 100F...when the inside temp sensor just starts to move off the bottom peg.........3 - 5 minutes depending on temperature.
Al this is critical to heat the precats and oxygen sensors FAST to enable the engine to go into closed loop operation as soon as possible
So that the oil is in the proper temperature range to LUBRICATE it is wise to not move the car until the coolant sensor reaches say 100F...when the inside temp sensor just starts to move off the bottom peg.........3 - 5 minutes depending on temperature.
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Gasoline has a vaporization point and the blend changes at least 4 times per year in a single location to attempt to match the average outside temperature.
The ideal range is pretty narrow unfortunately the injectors start flowing at some pretty cold temps and the gasoline won't evaporate until the intake valves reach a certain temperature [it reliquifies and coalesces into drops that don't burn] so every thing is double rich to try and make sure something [some part of it] burns.
When the idle smoothes out you know it is getting warm enough.
Remember the old choke well the injectors just double/triple up the fuel [cold enrichment as a function of coolant temperature and high idle to make sure it stumbles the least amount].
http://www.autoshop101.com/forms/h43.pdf
http://www.cruzinperformance.c....html
If you go BACK and Forward on above you will get a good tutorial on how engine ecu work!
The ideal range is pretty narrow unfortunately the injectors start flowing at some pretty cold temps and the gasoline won't evaporate until the intake valves reach a certain temperature [it reliquifies and coalesces into drops that don't burn] so every thing is double rich to try and make sure something [some part of it] burns.
When the idle smoothes out you know it is getting warm enough.
Remember the old choke well the injectors just double/triple up the fuel [cold enrichment as a function of coolant temperature and high idle to make sure it stumbles the least amount].
http://www.autoshop101.com/forms/h43.pdf
http://www.cruzinperformance.c....html
If you go BACK and Forward on above you will get a good tutorial on how engine ecu work!
Q45Tech, you must be two hundred years old to know everthing you do. Or just a very smart dude. Why haven't the car companies picked up on you and put you to good use at their design facilities. Oh yeah they dont want a car to go 200k. I could just imagine the recommended maint schedule if you wrote the car manual. Probably scare the customer away.
your stuff is always informative and correct. Thanks from me and I am sure many others
"The ideal range is pretty narrow unfortunately the injectors start flowing at some pretty cold temps and the gasoline won't evaporate until the intake valves reach a certain temperature [it reliquifies and coalesces into drops that don't burn] so every thing is double rich to try and make sure something [some part of it] burns." Is this the reason that my J smells gassy when just starting?
:bowdown
your stuff is always informative and correct. Thanks from me and I am sure many others
"The ideal range is pretty narrow unfortunately the injectors start flowing at some pretty cold temps and the gasoline won't evaporate until the intake valves reach a certain temperature [it reliquifies and coalesces into drops that don't burn] so every thing is double rich to try and make sure something [some part of it] burns." Is this the reason that my J smells gassy when just starting?
:bowdown
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Mayhem_J30
- Posts: 2643
- Joined: Tue Apr 30, 2002 2:00 am
- Car: Ummm...My Car
- Location: Louisville, KY
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Just 55 but this is my 173rd reincarnation worked my way back up from rodent. Sorry about the Black Plague just trying to prepare the Race for HIV.
Have to have seen the PBS[NOVA] special to get this one.Those whose ancestors survived have a partially protective gene making the white cell almost immune especially in double ancestors from the same region.......only the strong survived and it created a mutation that is with us today.
Much like the Q mutated to survive.
The under hood gas smell is from the metal fuel pipes shrinking in cold vs the rubber hoses when things warm up the leaks usually stop for a while.But the unburned gasoline out the tail pipe is what you suggest!
Have to have seen the PBS[NOVA] special to get this one.Those whose ancestors survived have a partially protective gene making the white cell almost immune especially in double ancestors from the same region.......only the strong survived and it created a mutation that is with us today.
Much like the Q mutated to survive.
The under hood gas smell is from the metal fuel pipes shrinking in cold vs the rubber hoses when things warm up the leaks usually stop for a while.But the unburned gasoline out the tail pipe is what you suggest!