TJ accelerator/RMP problem

Jeff_R said I’m having an intermittent problem with my 04 TJ. When I depress the clutch and simultaneously back off on accelerator when shifting, the RPM’s don’t immediately reduce like normal and in some cases they actually increase slightly before the RPM’s decrease. In other words, the RPM’s always go down but it is delayed or increases slightly before decreasing. In addition, when I’m having this intermittent problem, if I decelerate without depressing the clutch, I can feel a significant delay in deceleration as if the accelerator is sticking. About two years ago after doing some research, I replaced the throttle position sensor and it seemed to have helped for a short period of time but the problem reoccurred several months later. What could be causing this? If it was the throttle cable I would think it would be a chronic and not an intermittent problem. Has anyone ever experienced this or does anyone have any ideas what the problem might be?  

Jeff, it could be a vacuum leak, which can cause that problem, aside from a throttle cable that could have deposits on it that would  make it stick. Try a stronger return spring to test it out.

Do you happen to be running an aftermarket oiled air filter like a K&N?

kris_olof said Do you happen to be running an aftermarket oiled air filter like a K&N?  

No, just stock filter.

Jeff_R said

No, just stock filter.  

I see two likely culprits, vacuum leak as described above and sensor.

Easiest way to check vacuum leaks is to spray carb clean, starting fluid, or use an un-lit propane torch on the vacuum lines and intake seals and listen for idle changes.  Cold/cool engine only for the liquid sprays.  I had one when I got a larger throttle body and had to replace the MAP sensor seal to the throttle body housing.

Later TJs like ours had computers that can change the idle to prevent stalling.  In addition to the TPS there is also the IAC and MAP sensors.  A dirty throttle body (usually made worse by oiled air filters) allows buildup to occur on the sensors or on the butterfly valve and prevent perfect sealing.  Additionally sensors can fail leading to the computer changing RPMs.

Thanks for the help. It appears that I'm missing the throttle return spring. When I manually open the throttle I seem to get good return so I wasn't expecting it to be a spring problem. After doing some research it looks like I'm completely missing the throttle return spring shown at the bottom of this picture which I found on the internet:

I couldn't get the part locally so I called the dealership and they have it for about $7.00, a reasonable price since one company wanted $14 just to ship the part. The dealer told me that the part is discontinued but they have some back east so it will take a week to get here. I guess if it breaks in the future you just have to use some other type of spring and not the stock one. Hopefully this will solve the problem!

Maybe Oder extra