Lumpy idle after extended highway drives

[mclasser]

This is something I've noticed with my Infiniti since I've had it, but only after driving several hours on the highway. When pulling off the highway into a rest area, for example, the tach needle dances b/w 600-750 RPM at idle. There's some vibration in the steering wheel and armrest as well. Cold or hot weather makes no difference. This never happens with regular city or short(er) highway driving; idle's always a rock solid 750 RPM and smooth. Stuff I've checked, to no avail:

- No stored or active CEL codes.
- Cleaned MAF twice.
- Clean & tight battery connections.
- Checked air intake duct work for leaks.
- New air filters.
- Techron cleaner & Top Tier 93 fuel from different stations
- Clean fluids, topped off and bled of air.

There is no IACV since the throttle body's electronic. Nissan electronic TB's can act wonky when cleaned so I haven't touched it. AFAIK, the spark plugs & coils are original, so a tune up wouldn't be a bad idea. Car run's like a champ otherwise and gets 26 MPG on the hwy (rated at 24). This "issue," if I can even call it that, is not really bothersome since it happens so rarely.

Would love to hear some input.

 

[Revving2Redline]

Try running a mix of 93 pure and top tier 87 or 89 e10. I'm not a fan either,but as cold as its getting it could be running a bit rich. If your mileage has tanked try my method out. If e10 bothers you like it does me, give it a small couple teaspoons of gumout regane per fillup.

 

[ShotGun429]

EGR valve not seated after long highway drive.

 

[eljefino]

Originally Posted By: ShotGun429
EGR valve not seated after long highway drive.


x2

if you have a MAP sensor check its reading, you'll have less vacuum (more absolute pressure) due to the leak.

 

[JimPghPA]

Saved for future reference.