weird idling

[fujitsubo]

checked the other forum and didn't see anyone else have this problem. My jeep normally idles at 1000 rpm. Yesterday it creeped up to 1500 rpm at idle. When i engage into drive the jeep felt like pulling forward jerking as if i was pressing the gas and brake at the same time. In drive the rpm came down to normal but the jeep felt like going at minimum 1500 rpm which is considered fast. When i come to a stop, same thing, the jeeps feels like going forward but i was pressing the brake and the rpm stayed at 1500 rpm. It's almost dangerous, feels like i'm pressing gas and brake at the same time. Any advice thanks. This problem was exact replica on my Miata before i sold it so i didn't get a chance to know what the diagnosis is.

robert

 

[ms5490renegade]

you idle should be way lower than that

 

[aksloan]

Proper idle in park with engine at normal operating temperature should be 650rpm.

I'm new to the Libby world but I had a similar problem in a Ford and it was the IAC (Idle air control).

 

[flair1111]

just guessing here, but vacum leak??

 

[JeepJeepster]

Could be a bad/dirty 'intake idle control' sensor. Vacuum leak could also cause it.

The 3.7 should idle at/around 600rpms, not 1000.

 

[Treyz02KJ]

Is your cruise control working normally? usually a vacuume leak would be noticed there. I would say this is a situation to pay the dealership to hook up their fancy computer and diagnose this the easy way.

I agree though, very dangerous. Let us know what you find out.

 

[Treyz02KJ]

Oh, Does it idol higher even when its in neutral?

 

[fujitsubo]

rough idle

yes, right now it's idling higher in neutral, about 1500 rpm. If I change gear to D, the truck lurches and shift down to 1000 rpm. Really odd, looks like i'll have to bring it to the stealership to diagnosis. As for the cruise control, I don't use it at all as I enjoy using the pedal for my drives.

Oh, Does it idol higher even when its in neutral?

 

[fujitsubo]

Do you know if the Liberty has a air/flow meter? I didn't get any error messages.

robert

Could be a bad/dirty 'intake idle control' sensor. Vacuum leak could also cause it.

The 3.7 should idle at/around 600rpms, not 1000.

 

[JeepJeepster]

I do not think it has a air flow sensor. It does have a 'map' sensor on the front of the intake manifold and a IAT sensor though. The map sensor is used to determine the mass air flow of the engine though, it does so by calculating the density of the air.

Map=manifold absolute pressure
IAT=intake air temperature

 

[gramifications]

Is the check engine light on? If not then you won't get much help at a dealership. I would check the idle air controller and maybe the throttle cable and it's attachment to the throttle body. It sounds weird, but there could be something getting in the way of the free movement of the throttle plate stopping it from returning to the fully closed position. Also, how many miles? That might kinda help with a more accurate diagnosis.

 

[Welsh Dragon]

I have to agree this is the kind of problem that needs a hook up to get correct diagnosis - can work out cheeper in the end as there's too many possible causes - save you changing parts to rule out cause.

PS: Great colour us patriots have to stick together

Good luck

 

[gramifications]

I have to agree this is the kind of problem that needs a hook up to get correct diagnosis - can work out cheeper in the end as there's too many possible causes - save you changing parts to rule out cause.

I would agree, but if there isn't a check engine light on, there probably isn't an error code stored in the computer. Without an error code there isn't any information to point to what the problem is besides the symptoms he's already mentioned.

 

[fujitsubo]

Engine light came on. But when driving today, it seem fine and now the light went off. I'm getting a computer diagnostic first to see if they can identify the problem. My car only has 34,000 km (21,127 miles)

Is the check engine light on? If not then you won't get much help at a dealership. I would check the idle air controller and maybe the throttle cable and it's attachment to the throttle body. It sounds weird, but there could be something getting in the way of the free movement of the throttle plate stopping it from returning to the fully closed position. Also, how many miles? That might kinda help with a more accurate diagnosis.

 

[gramifications]

Thats good news, about your bad news (lol). If the engine light came on, and even if it's off now, there is a good chance that an error code was stored in the computer and that will help greatly when it comes to diagnosing your problem. Again, I wish you good luck in tracking down and fixing your problem.

 

[fujitsubo]

the diagnostic came back as low voltage on the TPS sensor. The "friendly" mechanic advised that problem can't be MAP sensor or a dirty throttle body at this point. He went on to tell me the TPS determines the shifting and gas/air ratio, something like that. Also because i don't drive my vehicle too much, the needle sensor might get dirty or corrode from not moving enough. Can you figure that one out?

 

[tjkj2002]

the diagnostic came back as low voltage on the TPS sensor. The "friendly" mechanic advised that problem can't be MAP sensor or a dirty throttle body at this point. He went on to tell me the TPS determines the shifting and gas/air ratio, something like that. Also because i don't drive my vehicle too much, the needle sensor might get dirty or corrode from not moving enough. Can you figure that one out?

The TPS sensor is the "throttle position sensor",it tells the PCM how open the throttle plate is,it does not in any way controll the air/fuel ratio,it can effect shifting but only downshifting when at wide open throttle(WOT),but the PCM uses the TPS sensor to help determine shift points,the O2 sensors control the air/fuel ratio,not the TPS sensor,he was blowing smoke up your a$$.It's a easy fix,about 30 min job to replace and most likely under $75 for the part.

 

[fujitsubo]

so are you saying i should change the 02 sensors then tjkj2002?

The TPS sensor is the "throttle position sensor",it tells the PCM how open the throttle plate is,it does not in any way controll the air/fuel ratio,it can effect shifting but only downshifting when at wide open throttle(WOT),but the PCM uses the TPS sensor to help determine shift points,the O2 sensors control the air/fuel ratio,not the TPS sensor,he was blowing smoke up your a$$.It's a easy fix,about 30 min job to replace and most likely under $75 for the part.

 

[tjkj2002]

so are you saying i should change the 02 sensors then tjkj2002?

No,clean the throttle body,most important is the IAC(Idle Air Control),that controls your idle.Your TPS sensor could be just bad also.Also look for vacuum leaks,they will raise your idle also.

 

[daniyel]

I've had leaks occur before on my old XJ on the intake gasket, which caused the idle to jump to 1200rpm (talk about a giant vac leak).