Skip the auto shop - Our mechanics make house calls

Q: High RPMs, but throwing the error code P0340.

asked by on

Went into get a hair cut, came out and my jeep started running at a high RPM and was throwing 3 error codes; P1391, P0171, and P0340. I bought a new Camshaft Position Sensor and installed it, I also did a visual inspection of all the wires, tubes, and springs related to the problems, and I rain 1/3 of a bottle of Seafoam through the engine. After that I cleared the codes and went for a drive to burn out the rest of the Seafoam. On the drive the P0340 came back up and the high RPMs returned. I have checked the wiring and, as far as I can tell, none of my vacuum lines are broken. I did not remove the lines, just visually inspected and ran my fingers over them to feel for abnormal imperfections. I am at a loss because the P0340 is suppose to get you a rough idle, not the high RPMs. So currently, with my foot off the clutch and gas, I can idle my car along in 3rd gear at 25 mph.

My car has 142000 miles.
My car has a manual transmission.

A: Hi there. These codes may or may not be rel...

Hi there. These codes may or may not be related to one another. I would be most concerned with the high idle first. Most of the time, on this engine it is due to a bad vacuum line. It sounds like you have checked those though. If the vacuum lines are fine, then most of the time the leak comes from the intake manifold gasket.

It is common for this to fail and cause excessive air to get into the engine and cause this high idle. The engine needs to be checked further for vacuum leaks. I would then check the crank sensor signal. If the crank sensor is not reading right, then it can throw a camshaft code like what you have. If you are looking to have this fixed, consider YourMechanic, as a certified technician can come to your home or office to diagnose the high idling symptom.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Put new brakes on, car feels like its in park when in drive/reverse

Hello. I will try to assist you with your 1999 Jeep. Remove the two wheels you worked on. Apply and release the service brakes several times and return to the wheel positions (with transmission in neutral, block rear wheels and...

Q: My check engine light is on reading code po171 lean

The code P0171 is for the engine control module is getting an O2 sensor lean bank 1 problem in the engine and has tried to compensate by making the injection system go rich on that bank. There is a long...

Q: turns over but win't start I can pop the clutch and it'll run fine till I shut it off then sometimes it will start others it won't

I can understand your frustration with your vehicle's starting issues. Since you are able to get the vehicle to start and run just fine when you "pop" the clutch, it is likely that you are having issues with your starter....

Related articles

P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.