2001 QX4 with 246K miles.
Problem - Intermittent rough idle / miss when idling in gear (e.g. Drive) but goes away when idling in Park. Understand engine is under load when in gear vs park and thus RPM is lower in gear vs park. Drive fines with no miss at speed.
Need input on possible cause of above problem. No DTC codes. Reference below work performed recently, past and future planned. No
Recent corrective work performed by me relative to potential cause of problem:
- Replaced all vacuum lines (Now pulling 16 in. of vacuum)
- Replaced spark plugs with NGK PLRF5A-11
- Replaced 3-pin coil connectors (Validated spark for all cylinders with coils out, spark plug attached, turn engine over with fuel pump fuse out)
- Replaced fuel filter
Past work performed by me relative to potential cause of problem:
- Cam Sensor
- Mass Air Sensor
- Swirl Cntl Valve
- O2's (All Four)
Future work planned by me:
- Valve cover gaskets / plug seals (Significant leak on rear passenger side valve cover)
- Fuel injectors
- Coils
Intermittent Rough Idle in Drive, OK in Park
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atraudes
- Posts: 1106
- Joined: Thu Jan 10, 2013 7:46 pm
- Car: 2001.5 Infiniti QX4 4WD
- Location: Sammamish, WA
Re: Intermittent Rough Idle in Drive, OK in Park
There are quite a few things that can cause a rough idle. I'll run down some of the simple ones I've encountered.
16 seems a bit low for your vacuum. When I last measured mine it was -22 psi. Was that in park or in drive? Poke your head around the engine compartment with the engine running and carefully listen for any hissing sounds indicating a vacuum leak.
Pull the vacuum hoses off the fuel pressure regulator and fuel damper and see if you get a strong smell of gasoline. If you do, run the car with the stinky hose off for a few minutes and see if fuel leaks out the vacuum port. If it does, the part's bad. Fuel leaking into the vacuum lines will get sucked into the intake manifold and cause it to run rich, which can cause a rough idle.
Pull the intake ducting off and take a look at the throttle body. If it has carbon buildup in it, that will also cause idle issues. If it's dirty, remove it and clean the snot out of it with throttle body cleaner.
If everything else checks out, check your fuel pressure and make sure it's not too low. You can borrow a gauge from most parts stores and measure it at the fuel rail.
Good luck and let us know what you find!
16 seems a bit low for your vacuum. When I last measured mine it was -22 psi. Was that in park or in drive? Poke your head around the engine compartment with the engine running and carefully listen for any hissing sounds indicating a vacuum leak.
Pull the vacuum hoses off the fuel pressure regulator and fuel damper and see if you get a strong smell of gasoline. If you do, run the car with the stinky hose off for a few minutes and see if fuel leaks out the vacuum port. If it does, the part's bad. Fuel leaking into the vacuum lines will get sucked into the intake manifold and cause it to run rich, which can cause a rough idle.
Pull the intake ducting off and take a look at the throttle body. If it has carbon buildup in it, that will also cause idle issues. If it's dirty, remove it and clean the snot out of it with throttle body cleaner.
If everything else checks out, check your fuel pressure and make sure it's not too low. You can borrow a gauge from most parts stores and measure it at the fuel rail.
Good luck and let us know what you find!
-
atraudes
- Posts: 1106
- Joined: Thu Jan 10, 2013 7:46 pm
- Car: 2001.5 Infiniti QX4 4WD
- Location: Sammamish, WA
Re: Intermittent Rough Idle in Drive, OK in Park
Did you happen to find out what was causing the rough idle for you? I'm having the same issue but naturally nothing I suggested lead anywhere.