Sudenly higher RPM at idle

Suddenly higher RPM at idle

Hello everyone. A day ago, while I was driving I felt like something happened with the engine, I did not depress the throttle pedal more than I needed at that moment, but car slightly accelerated. I put the engine on idle and tacho shows 1000/1100 rpm instead of usual 850/900. Engine temp gauge shows normal temp. Today same thing. Cold engine ok, after warmed up at normal temp, it started acting, goes to 1000/1100rpms then by itself goes to normal. After a few seconds it is ascending again and so on. Then I turn engine off and start again, rpms go up to 1500 then to 1000/1100 and after 4-5 sec. go to normal, then again to 1000/1100... Tried to change relays 109 and 103 - no result. Strange - before engine starts, glow plug light stays on for some 10-15 secs then goes off and no matter it is off or on, engine starts without problem. If engine is cold (e.g.morning), gp light goes off as it should and all is well till eng warmes up to normal... No repair to the engine last 12 months (15k mi) except oil change, fuel/air filter replacements (last year), cabin filter (today) and usual oil refilling after some 1000-2000mi (100-300g.). Never had experience like this, I do not know what to think, getting more and more nervous. Help!
P.S. Car pulls well, no any other problems.

Limp mode for a failed accelerator pedal position sensor is a high idle. Maybe it's starting to fail.

LLL said:

Hello everyone. A day ago, while I was driving I felt like something happened with the engine, I did not depress the throttle pedal more than I needed at that moment, but car slightly accelerated. I put the engine on idle and tacho shows 1000/1100 rpm instead of usual 850/900. Engine temp gauge shows normal temp. Today same thing. Cold engine ok, after warmed up at normal temp, it started acting, goes to 1000/1100rpms then by itself goes to normal. After a few seconds it is ascending again and so on. Then I turn engine off and start again, rpms go up to 1500 then to 1000/1100 and after 4-5 sec. go to normal, then again to 1000/1100... Tried to change relays 109 and 103 - no result. Strange - before engine starts, glow plug light stays on for some 10-15 secs then goes off and no matter it is off or on, engine starts without problem. If engine is cold (e.g.morning), gp light goes off as it should and all is well till eng warmes up to normal... No repair to the engine last 12 months (15k mi) except oil change, fuel/air filter replacements (last year), cabin filter (today) and usual oil refilling after some 1000-2000mi (100-300g.). Never had experience like this, I do not know what to think, getting more and more nervous. Help!
P.S. Car pulls well, no any other problems.

Click to expand...

Not exactly sure where you're located in Europe but I would think a 10-15 second GP light during this time of year would not be right.

That to me would say I needed to check the coolant temp sensor or the wiring to that sensor.

Whether this is involved in your idle situation I cannot say, but I will say that there was a recent thread about someone who had a problem with the fuel stop solenoid o-ring which was causing some idle irregularites. That thread should be pretty recent I think.

Are you getting an error code with this condition? I would expect that if it was the accelerator pedal going bad that a code would be triggered since that is directly connected to the ECU.

Steve

KLXD said:

Limp mode for a failed accelerator pedal position sensor is a high idle. Maybe it's starting to fail.

Click to expand...

No limp mode (power loss, right?), car pulls very well... where is located that "pedal position sensor"?
Steve Addy, yes, strange gp light for temp of 25°C! It was all ok two days ago.
"...someone who had a problem with the fuel stop solenoid o-ring which was causing some idle irregularities"... My IP was repaired last year and I have no leaks at all. Can't tell you about the error code, at this moment no possibility to connect to vag-com...

LLL said:

No limp mode (power loss, right?), car pulls very well... where is located that "pedal position sensor"?

Click to expand...

NO!

Limp mode meaning a programmed response by the ECU to a certain condition.

In your case a possibly a malfunctioning pedal position sensor. It lets you get home or at least off the road if the pedal goes dead

Limp mode for various other failures is low power.

It's above and linked to the accelerator pedal.

The fuel stop solenoid o-ring can not cause this or any other problem other than a leak. There is no room for it to get out of place after installation like the pictures show. If it wire installed that way it would be deformed and would've leaked.

Above...

Is that "pedal position sensor" the black lookalike cylinder
thing above the accelerator pedal? If it is and if this is the
problem, it would be pain in a** to replace it.

That's it. I've never had to replace it but often the pedal and sensor are an assembly that bolts to the floor.

Well, thanks a lot.
P.S. Does the Vag-com or OBD will
show where the exact problem is?

VCDS (Vag-Com) might. I doubt an OBD scanner will.

I can't remember if VCDS will display the "Throttle" position in a test mode. Maybe someone else knows.

I'm not saying it's your problem. I don't know if you'd get the high idle and still have the pedal function.

On my Dodge I was getting a code for the pedal position voltage low but it worked fine. Just had to adjust it.

The Vag-Com will show throttle position and it can be logged.

Strange ting... yesterday the glow plug light went off as it should at temps of 34°C - immediately! And during the drive I did not notice any abnormality of the engine work, no fluctuating rpms, it works like before, perfect! So I think there's a connection between the glow plugs light not going off for 15-20 secs and the irregular rpms... I'm confused.

LLL said:

Strange ting... yesterday the glow plug light went off as it should at temps of 34°C - immediately! And during the drive I did not notice any abnormality of the engine work, no fluctuating rpms, it works like before, perfect! So I think there's a connection between the glow plugs light not going off for 15-20 secs and the irregular rpms... I'm confused.

Click to expand...

I think it would be unusual if there was some connection. The long GP light is most likely due to faulty engine coolant temp sensor but it would be unusual for that to cause a problem with idle.

I would be surprised if there wasn't a code stored but who knows, maybe not.

Drive it until it happens again, and it will happen again, these things rarely go away by themselves.

Steve

Well, I'm really confused. If it happens again, should I replace all the assembly, accel. pedal/black cylinder? With used one off course. Any pictures of disassembling? Thanks a lot guys!

Last two days the problem came back. And it came back with the gp light staying on for 10-15 seconds! (Sigh).

Same things today, glow plugs on for 15 secs (outside temp. +35°C/95°F), rpms around 1000/1100 on idle... Next week I'm changing the coolant temp sensor, I hope the gp light will go back to normal.
I found the following text somewhere on the internet, about the high rpms:
"High engine idle can be caused by a number of different things. A stuck/binding throttle, vacuum leak, bad throttle position sensor, coolant or air flow sensor all can be the cause of a high idle speed".

You need to scan it to see if any Codes are set.

Coolant temp.sensor changed this morning (gp light works like it should), drove some 20mi, all was ok. We'll see this week what would happen further.

40 miles today, downtown, hot weather +95°F, engine works like a charm... no high rpms. Continuing test to the end of the week.

Another 40 miles today, same weather, city drive... no high rpms, yay! Test is continuing tomorrow.

Good deal.

Today and yesterday, 50 miles, all is ok.
I think I can "close" this post with conclusion
that the broken coolant temperature sensor can
cause the problem described in my first post.
Thanks for the help to all of you guys!

Yesterday I had a 200mi combined city/open road trip.
Rpms normal, glow plug light behaving normal also,
outside temp around 95°F, so I can confirm: one of
the problems causing incorrect gp on/off light and high
rpms at idle is the broken coolant temperature sensor!
CTS part# 357919501A