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-   -   Weird engine issue (http://www.wranglerforum.com/f210/weird-engine-issue-29413.html)

iamadam1122 04-20-2009 03:00 PM

Weird engine issue
 
I have a 2004 6cyl 5spd. If I'm sitting still in neutral and hold the throttle so the tach stays at 2500rpms it will randomly raise without my foot or the pedal moving one bit. It doesnt matter what rpm and I think it does it while driving too its just not as noticeable. It seems like im on and off the gas but in reality the pedal is completely still.

Anyone know whats going on?

I tried searching but its hard to search because i dont know what to call the problem

slf41002 04-20-2009 06:23 PM

I would say the TPS(Throttle position sensor) is bad. Do a search on that.In case you are not familiar.There are a few posts on it and how to replace/location.Anyway I would bet that is your problem.It is and has been in the past a know issue with the 4.0L from Wranglers to Cherokees.

Hebera 04-21-2009 10:51 AM

how far will the RPM's raise? Will it just keep going up steadily or does it top off at some point?

MOz 04-21-2009 11:01 AM

Quote:

Originally Posted by iamadam1122 (Post 358153)
I have a 2004 6cyl 5spd. If I'm sitting still in neutral and hold the throttle so the tach stays at 2500rpms it will randomly raise without my foot or the pedal moving one bit. It doesnt matter what rpm and I think it does it while driving too its just not as noticeable. It seems like im on and off the gas but in reality the pedal is completely still.

Anyone know whats going on?

I tried searching but its hard to search because i dont know what to call the problem

X2 - clean out or change your TPS sensor.

slf41002 04-21-2009 11:06 AM

I would just replace it and clean your throttle body really good while at it.You may also have carbon and or fuel varnish build up in the TB keeping the butterfly from closing all the way.

Jerry Bransford 04-21-2009 11:08 AM

It only does it when you hold the engine rpms at 2500 with your foot on the accelerator pedal? Why are you doing that?

That reminds me of the guy who tells the doc that his shoulder hurts when he moves his arm in a certain way. The doc then says "Then don't move your arm like that". :p

iamadam1122 04-26-2009 02:17 PM

Quote:

Originally Posted by Jerry Bransford (Post 358635)
It only does it when you hold the engine rpms at 2500 with your foot on the accelerator pedal? Why are you doing that?

That reminds me of the guy who tells the doc that his shoulder hurts when he moves his arm in a certain way. The doc then says "Then don't move your arm like that". :p

no it happens all the time i only said that because it cant hold a certain rpm. It does the same thing at any rpm while driving, it will accelerate on its own a few mph and then slow back down.

I got a new TPS and no difference. If i start off in 1st, let off the gas, change to second, and begin to let the clutch out while getting back on the throttle nothing happens for a second or 2. its like the pedal does nothing. then suddenly it starts working and lurches forward making me look like an idiot. Its most noticable in the lower gears because, well theyre lower and more sensitive i guess.

iamadam1122 04-26-2009 02:18 PM

Quote:

Originally Posted by Hebera (Post 358626)
how far will the RPM's raise? Will it just keep going up steadily or does it top off at some point?

tops off around 3500 then lowers back down. a few more seconds later it rises again.


Only has 40,000 miles if that makes any difference. Going to clean the TB right now.

rrich 04-26-2009 03:00 PM

Have a close look at the thin little plastic vacuum line to the MAP sensor on the firewall. Make sure it's not pinched or kinked. Make sure the rubber adapters at the ends aren't cracked or loose.

Does it do it when it's stone cold, at just at normal temp, or all the time no matter what the temp (open or closed loop?)

Does the voltmeter on the dash float up and down when it does it? If yes, check the battery voltage right at the battery to see it it varies there too. Make sure the battery connections are tight, even though it starts fine.

Turn your radio to AM, then between stations - do you hear a loud whine? Even a portable radio held close can hear it.
Sometimes an alternator with a bad rectifier diode - or diode trio - can cause strange seemingly unrelated things to happen - the system voltage to the ECM is affected, driving it nuts!

350chevrolet 04-26-2009 06:40 PM

'04 with 40000 on it, isnt it still under factory warranty? if so make jeep fix it. otherwise id pull the tb off and clean it then have a smoke test done to see if it has a small vacuum leak somewhere.

maperry 06-04-2009 12:21 AM

I had the same problem on my 2003 wrangler. I got a code for the TPS and after replacing the TPS the code was still there. What ended up happening was water got into my steering wheel and messed up the clock spring. The cruise control sends a 5 volt signal to the TPS, and if the clock spring goes bad this signal can not get to the TPS and the TPS sends erratic signals to the ECU. The problem went away when I removed the connector to the clock spring under the steering wheel. Try disconnecting the clock spring and see if the problem goes away, if it does then it will cost you about $320 to get the repair from the dealership, or about $120 if you can do it yourself. You can drive with the clock spring disconnected, but you will loose your cruise control, horn, and drivers side airbag.

yjwes 06-04-2009 12:49 AM

im with every one on this sounds like a TPS i had one doing the same thing

rrich 06-04-2009 02:17 AM

Usually when a TPS fails it becomes intermittent. Remember when radios had knobs for volume controls? They were potentiometers, variable resistors, essentially the same as a TPS. The old volume controls became "scratchy" - they'd get dirty or worn and the contacts would get intermittent.
But once the volume control was set, it worked fine. When you moved the knob it made all kinds of sounds.

The TPS, being the same idea, also becomes scratchy or dirty. It's not sealed, and a common failure after steam cleaning or hosing off the engine.

But - once it's "not moving" - like you are doing holding your foot steady, it usually doesn't cause trouble. Accelerating or decelerating - moving your foot causes the engine to jump and jerk.

I won't rule it out completely, but --.
What I suspect, and another recent post was very similar - was the computer somehow got a spike or noise inadvertently loaded into it's memory.

Simply disconnect the battery overnight. That will erase both the short and long term memories. You have to leave it off for an extended period of time to work.


Look back 3 pages of posts, for a very similar problem, entitled "2005 wrangler lunges while idling."

The guy said it did the trick for him. Try it!


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