Jeep TJ Sensitive Throttle

[kstalker]

Hi All, I'm chasing down some high frequency vibrations on my stock 1999 Jeep TJ Sport 4.0 Auto, and am trying to sort out if my throttle sensitivity is normal. TPS reading at idle is 15.3%, and it revs up to 2,000+ RPMS with only about 1% throttle input, bringing it to around 16.3%ish. Is it normal to be this sensitive, or could this be an indicator of an issue causing the engine to surge with very minor throttle?

Engine idles well, but feels like it has a lot of vibration under load (even when stationary) between idle and 2,000 RPMS. O2 sensor seems to have a normal oscillation, and TPS sweeps smoothly up to around 75%

 

[Chris]

Hi All, I'm chasing down some high frequency vibrations on my stock 1999 Jeep TJ Sport 4.0 Auto, and am trying to sort out if my throttle sensitivity is normal. TPS reading at idle is 15.3%, and it revs up to 2,000+ RPMS with only about 1% throttle input, bringing it to around 16.3%ish. Is it normal to be this sensitive, or could this be an indicator of an issue causing the engine to surge with very minor throttle?

Engine idles well, but feels like it has a lot of vibration under load (even when stationary) between idle and 2,000 RPMS. O2 sensor seems to have a normal oscillation, and TPS sweeps smoothly up to around 75%

A TPS reading of 15.3% at idle is typically on the higher side for a TJ, which usually has a reading close to 0% at idle (that's what I found from searching). The fact that you're seeing such a small input causing a spike to 2,000+ RPMs could indicate that there might be an issue with the throttle position sensor itself or possibly with the throttle body.

Let us know what you find!

 

[macleanflood]

For reference...this might help...

Thread 'How to clean your IAC (Idle Air Controller) valve'

Jan 2, 2016

If you're experiencing idle issues on your Jeep Wrangler TJ the most likely culprit (and the first thing you should check) is your IAC (Idle Air Controller). Often times the IAC gets very gunked up causing the Jeep to idle improperly. A simple cleaning is usually all it takes to get it running as good as new.

If you end up needing to replace your IAC valve (they do fail on occasion), you can find the part numbers (and the links to purchase them on Amazon) below:

2005-2006 IAC Valve (Part # 4861552AC)
1997-2004 IAC Valve (Part # 4874373AB)

There is no need at all...

• Chris
• iac idle idle air controller idle valve
• Replies: 191
• Forum: TJ How-to Guides

• 

-Mac

 

[GregBelleville]

The vibrations your feeling could also be worn out transmission mount or motor mounts, might want to check those too.

 

[kstalker]

A TPS reading of 15.3% at idle is typically on the higher side for a TJ, which usually has a reading close to 0% at idle (that's what I found from searching). The fact that you're seeing such a small input causing a spike to 2,000+ RPMs could indicate that there might be an issue with the throttle position sensor itself or possibly with the throttle body.

Let us know what you find!

Interesting, my understanding is that an idle TPS reading of a % in the teens was normal, I'll keep digging. Appreciate the response.

 

[kstalker]

For reference...this might help...

Thread 'How to clean your IAC (Idle Air Controller) valve'

Jan 2, 2016

If you're experiencing idle issues on your Jeep Wrangler TJ the most likely culprit (and the first thing you should check) is your IAC (Idle Air Controller). Often times the IAC gets very gunked up causing the Jeep to idle improperly. A simple cleaning is usually all it takes to get it running as good as new.

If you end up needing to replace your IAC valve (they do fail on occasion), you can find the part numbers (and the links to purchase them on Amazon) below:

2005-2006 IAC Valve (Part # 4861552AC)
1997-2004 IAC Valve (Part # 4874373AB)

There is no need at all...

• Chris
• iac idle idle air controller idle valve
• Replies: 191
• Forum: TJ How-to Guides

• 

-Mac

I've cleaned the IAC a couple times, doesn't seems to make a difference. It also hums along nicely at idle, just revs way up as soon as you nudge the throttle.

 

[kstalker]

The vibrations your feeling could also be worn out transmission mount or motor mounts, might want to check those too

Had the same thought, have replaced both motor mounts and the trans mount.

 

[Chris]

Interesting, my understanding is that an idle TPS reading of a % in the teens was normal, I'll keep digging. Appreciate the response.

Let me know what you find in regard to this number. Have you checked the FSM by chance? It seems like it should have something definitive in there.

 

[macleanflood]

Possible your throttle cable is too short? Is it an OEM?

Original throttle body?

-Mac

 

[Gilaguy23]

How you guys getting a % of TPS voltage? It was always .6ish at idle and up to 5V at WFO with a DVM.

 

[kstalker]

Let me know what you find in regard to this number. Have you checked the FSM by chance? It seems like it should have something definitive in there.

Per the FSM:

"With the ignition key in the ON position, check the
TPS output voltage at the center terminal wire of the
connector. Check this at idle (throttle plate closed)
and at Wide Open Throttle (WOT). At idle, TPS output
voltage should be greater than .26 volts but less
than .95 volts."

So it looks like there is a range of acceptable values. I pulled mine from a scanner, but I'll try putting a voltimeter under the hood tonight.

 

[Chris]

Per the FSM:

"With the ignition key in the ON position, check the
TPS output voltage at the center terminal wire of the
connector. Check this at idle (throttle plate closed)
and at Wide Open Throttle (WOT). At idle, TPS output
voltage should be greater than .26 volts but less
than .95 volts."

So it looks like there is a range of acceptable values. I pulled mine from a scanner, but I'll try putting a voltimeter under the hood tonight.

Cool, let us know what numbers you get with the multimeter. That should be telling!

 

[GoldenGorilla]

Hi All, I'm chasing down some high frequency vibrations on my stock 1999 Jeep TJ Sport 4.0 Auto, and am trying to sort out if my throttle sensitivity is normal. TPS reading at idle is 15.3%, and it revs up to 2,000+ RPMS with only about 1% throttle input, bringing it to around 16.3%ish. Is it normal to be this sensitive, or could this be an indicator of an issue causing the engine to surge with very minor throttle?

Engine idles well, but feels like it has a lot of vibration under load (even when stationary) between idle and 2,000 RPMS. O2 sensor seems to have a normal oscillation, and TPS sweeps smoothly up to around 75%

I have noticed with a standard ODBII reader and app such as Torque that the TPS readings are not accurate and range from somewhere in the 14-15% low end to 75% at wide open throttle. Obviously not correct.

When I scan with HP Tuners VCM Editor and chose the channels for the PCM I get accurate readings from 0-100% and the accurate IAC readings.

With that said I have seen the IAC hold open with the throttle position report 0.0% at 2200rpm before. In my case because of an error in my programming.