I just noticed this thread today. I have always had the same problem with RPM at highway speeds which you are describing, but i think that is just the way it is. mine passes 2k rpm at about 49 mph, getting to about 2.5k at 60mph highway speeds. (makes me wish i had a six speed)

I would agree with the poses on the first page. The gague cluster seems to have problems with its electronics when it is hot/cold, and I believe what you are seeing is the gauges themselves lying about your speed or rpm.

 

after that was posted i ran tests while driving and concluded that that the gauge cluster is accurate and as stated in my last post (although not entirely sure which change made the most difference) the problem has been reduced tremendously.

 

Its back!!!!!

Maybe it never went away and i couldnt tell cause i havent driven that far till today, IDK

its just as bad or worse and i noticed when i came to a stop at a redlight after making the long trip that the idle was also up to 1k.

Its possibly the fact that i think my fitv is malfunctioning.

Any thoughts?

 

I'll try to get creative on this one.

Do you have a smart phone, or a GPS? Check that your speedometer is giving you an accurate reading.

Also, how are you calculating your gas mileage? What is bad gas mileage vs good gas mileage?

 

to ensure an accurate speedo i had a friend of mine who is a cop follow me with his radar and everything was dead on.

when i say bad im meaning before this started i was getting 30+ mpg now im 25 at best but mostly less than that

I wanna think theoretically it could be the malfunctioning fitv but im wondering if my cat is clogging or the front o2 is malfunctioning and not setting the cel for some reason. It definitely get worse the further i drive and car heats up/ cycles from open to closed loop

The longer the drive (especially at higher/highway speeds) it gets worse and worse until i park for a while and everything cools backs down.

On my way home tonight from a 80 mile trip it got to the point where as i was getting close to being home it was barely hitting 50mph at 2k in 5th when i easily do 65 in 5th at 2k when its "cold".

Also as previously posted, i also noticed tonight when nearly home when stopped at a red light it was idling at 1k when normally it idles either at 600(completely cold) or 750(slightly warmed up/ short drive)

 

Odd behavior. The calculator at:

ctny.audiworld(dot)com/mark/s4/gears/gear_calc(dot)html

...shows 51.7mph @ 2K RPM in fifth gear with new 195/60 15s and coupe/sedan final drive. Either the speedometer isn't right when it's cold or, as Poorman mentioned, the clutch is slipping. But it doesn't sound like a slipping clutch because that usually shows up on hills, not on flat road/steady throttle driving.

The cold idle too low or the tach is wrong. Cold idle should be around 1400 RPM.

You may want to connect an external tach to the tach test connector and compare its reading to the dash tach while driving. Maybe the gauge cluster is intermittently bad, showing incorrect speeds &/or RPM?

 

My fault, To clarify when i first start the car it idles at about 1200 for a minute or two then drops to the lower rpms i mentioned before.

I will test the cluster but it seems the cluster is working specially the speedo as i had my cop friend tail me around starting at cold start in my driveway and then driving around letting it reach op temp etc..

 

although i already have one good possible cause that i am going to check into thanks to my buddy poorman a "POSSIBLE" clue presented its self today.

As i was leaving the house this morning to make a 160 mile round trip the cel popped on, stopped, checked the code "p0420", reset the light and made my trip and the light never came back on.

So possible insight into what may be causing this but dont why it randomly came on and never re-tripped after reset.

Any ideas, questions, or comments?