I have a bit of an involved problem, so I’ll break it down a bit and try to provide as much detail as possible.
My main problem:
I have a rough idle on my 2001 Infiniti QX4. It’s not extremely rough, but quite noticeable. It doesn’t happen all the time, though it happens most often after going up a hill, getting off the freeway, or after heavy acceleration.The next stop after a few minutes of slow easy driving usually yields a smooth idle again. Acceleration and all other driving is super smooth with no hiccups or loss of power.
The only other problem is warm startups are weak, as if engine was starved of air. When cold the engine starts up with no problem or hesitation.
The state of things:
New parts (all replaced within the last year):
- fuel pump
- fuel filter
- fuel damper
- fuel pressure regulator
- fuel hoses
- vacuum lines
- coil packs
- spark plugs
- idle control valve
- The air filter is a K&N cone that’s part of a CAI and is mostly clean (can still see the color and metal mesh).
- The hose attached to the fuel damper reeks of fuel, but doesn’t leak fuel out of the port when I pull the hose and run the engine for a few minutes.
- The fuel pressure regulator’s vacuum port doesn’t smell.
- I don’t hear any vacuum leaks, and the CEL is not on.
- Fuel pressure and manifold vacuum are perfectly within range per the FSM and are rock steady.
- I cleaned the throttle body recently and removed all carbon buildup.
- I only use 92 grade (per manufacturer’s recommendation) from Chevron.
What I’ve tried (beyond the new parts):
- I’ve swapped in and returned five other fuel dampers from various retailers including the dealership, and all immediately exhibit the same symptom.
- I’ve replaced the vacuum line each time, and the smell is present after driving a few miles.
- The ends of all of the dampers have the same part numbers and stampings despite being sold under different brands, so I believe they’re actually all the same manufacturer: SMP. I’ve contacted SMP and the dealership and both shrugged their shoulders and refuse to do anything citing that they’ve never received complaints.
- I bought a scan tool that shows sensor information and drove around watching the fuel trim. I watched the long-term because short-term was very erratic and hard to get a good picture from. For the most part, it didn't go any lower than -5%, except for once or twice when it jumped down to -7%. The 1 and 2 values usually differed by 2%, with 2 being the closer to 0. Idle when not moving was always 0%. Going up a hill at 3k, the two numbers both settled at -2.3%. With no throttle applied and moving at about 30mph, the numbers were between -1 and -3%.
- Any ideas on what could be causing the rough idle?
- Should the fuel damper be leaking fuel at all? This seems like the obvious smoking gun but the manufacturer’s adamance that it’s not a problem and it not weeping fuel sans vacuum hose introduces some doubt.
- Any ideas on other damper manufacturers to try or if I should? I haven't tried Borg Warner or Airtex/Wells, but BWD are hard to come by and are a subsidiary of SMP so are likely the same part anyway. Airtex/Wells have a horrible reputation from what I’ve seen and I’m afraid I won’t be able to return them as they’re sold online by a place I haven’t done business with. The fuel pressure regulator is also SMP, for what it’s worth.