Higher than usual rpm this morning

[Capricorn]

While driving on the highway this morning to work, I noticed my tachometer was showing higher than usual rpm in each gear.
At 65mph in 5th or 6th gear I should be seeing 2200/2000rpm on my RubiJL. But the tachometer was showing around 2800-3000 at that speed in 5th or 6th gear.
It is a new Jeep - just touched 1100 miles.

Any ideas? Computer problem?

My oil temperature was normal - on a 20 mile trip, I never exceeded 205F. No funny smell either. No error messages either.

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[The_Phew]

Someone snuck into your garage and installed 4.88 gears?

 

[Capricorn]

Someone snuck into your garage and installed 4.88 gears?

It feels exactly like that.

 

[Capricorn]

I am making an appointment with the dealership to look at.
Here is something unusual I noticed. Even when the engine is off, the tachometer does not go down to zero - it is stuck at around 400rpm.

 

[Capricorn]

Just for the heck of it, I opened up the hood and took a look at the fuse and relay box. There were many which were not seated properly because I can hear some clicks as I pressed them. After a while I also noticed that the trahometer which was at 400rpm in the off position went down to zero, and when I drove to the dealership - about 12 miles drive, the rpm was back to normal levels for the speed and the gear.

The dealership told me to leave the Jeep with them for a detailed diagnosis and repair if it happens again next time.

Drove back home (another 10 miles) and still no issue.

PS:

Anyone from Jeep Care around on this forum? I request this to be documented in case if this turns into a bigger issue. Thanks!

 

[Capricorn]

I wonder if a loose fitted fuse was indeed the issue.

https://www.yourmechanic.com/services/engine-idle-speed-is-high-inspection

Common reasons for this to happen:
Faulty Fuse: In the majority of vehicles, engine idle speed is controlled via an idle control valve (ICV). A faulty or blown fuse in other electronically controlled systems can cause the IAC motor to malfunction, leading to a higher than normal engine idle speed.

Faulty Idle Control Valve (ICV): The job of the idle control valve is to maintain and control a consistent idle speed. The ICV will help counter any extra loads put on the engine such as lights, stereo and air conditioning. This part will often malfunction due to excessive carbon buildup in the intake manifold.

Vacuum Leak: On a fuel injected engine a vacuum leak will cause a high engine idle. The engines oxygen sensor will detect the extra oxygen entering the engine via the vacuum leak which will alert the engine’s computer that the exhaust is running lean, which will prompt the computer to pump in additional fuel, resulting in an abnormally high idle.

Malfunctioning Throttle: A malfunctioning throttle system can cause both a high idle as well as an engine stall. A dirty air intake or cracked air intake tube is often the culprit.

Computer Malfunction: A computer malfunction can cause a high engine idle, especially the powertrain control computer. If it misinterprets the information it is receiving about the current idle speed, a high idle speed may be the result.​

 

[mwilk012]

I wonder if a loose fitted fuse was indeed the issue.

https://www.yourmechanic.com/services/engine-idle-speed-is-high-inspection

Common reasons for this to happen:
Faulty Fuse: In the majority of vehicles, engine idle speed is controlled via an idle control valve (ICV). A faulty or blown fuse in other electronically controlled systems can cause the IAC motor to malfunction, leading to a higher than normal engine idle speed.

Faulty Idle Control Valve (ICV): The job of the idle control valve is to maintain and control a consistent idle speed. The ICV will help counter any extra loads put on the engine such as lights, stereo and air conditioning. This part will often malfunction due to excessive carbon buildup in the intake manifold.

Vacuum Leak: On a fuel injected engine a vacuum leak will cause a high engine idle. The engines oxygen sensor will detect the extra oxygen entering the engine via the vacuum leak which will alert the engine’s computer that the exhaust is running lean, which will prompt the computer to pump in additional fuel, resulting in an abnormally high idle.

Malfunctioning Throttle: A malfunctioning throttle system can cause both a high idle as well as an engine stall. A dirty air intake or cracked air intake tube is often the culprit.

Computer Malfunction: A computer malfunction can cause a high engine idle, especially the powertrain control computer. If it misinterprets the information it is receiving about the current idle speed, a high idle speed may be the result.​

All of these are talking about actua high idle speed, yours sounds like it was just indicating high. If you took it to the dealership they would likely replace the instrument cluster, as it is a similar issue to the speedometer reading high that has been seen here.

 

[Capricorn]

All of these are talking about actua high idle speed, yours sounds like it was just indicating high. If you took it to the dealership they would likely replace the instrument cluster, as it is a similar issue to the speedometer reading high that has been seen here.

I was seeing actual higher than normal RPM both in idle as well as in driving - it wasn't just a display.
The 6th gear was acting like it was the 4th gear and I felt the extra acceleration in 5th and 6th on the highway. And I was not able to duplicate this issue since I snapped back in some of the loose fuses. I'll see how it goes for the next few days.

 

[mwilk012]

Even when the engine is off, the tachometer does not go down to zero - it is stuck at around 400rpm.

This seems to be your problem though. Your gearing can't just change, its a physical drivetrain. Could you describe in more detail what you mean by 6th gear felt like 4th?

 

[Capricorn]

This seems to be your problem though. Your gearing can't just change, its a physical drivetrain. Could you describe in more detail what you mean by 6th gear felt like 4th?

By that I mean the RPM I was seeing (2800 - 3000) in 6th gear at 65-70mph is what I should see in 4th gear for the same speed.
True, gearing can't suddenly change. But is it possible that engine speed was being increased by the PCM?

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