Problem with jumpy/bumpy gas pedal -

[(O|||||O) in SB]

I just bought a 2001 4 banger - all stock except the 31" BFG tires. Only 17,000 street miles.

I know I need to regear or swap with Rubicon axles (I like this idea).

First I need to deal with what I call a jumpy/bumpy gas pedal. Not very technical but that's what happens. When going over bumps with my foot on the gas pedal, the gas pedal overreacts and causes the jeep to jerk. The only way I have found to avoid this is to not have my foot on the gas when going over bumps. That's no way to drive a jeep.

This happens in 2 wheel drive, 4 -wheel and 4 lo. It happens going slow and going faster. I have noticed that when I am accelerating up a hill, I do not have the jumpy/bumpy problem.

It seems like this problem is more than just the gears.  Are there adjustments in the gas pedal mechanism/system? Pedal spring, cable, throttle?

Any ideas? Thank you.

[Jeffy]

When you say jerk what do you mean?  Now that I've reread it, I'm thinking you migth be experiancing bumpsteer.  Please explain what's actually happening.

[(O|||||O) in SB]

First I want to say that I have driven my son's Tacoma 4X4 stick shift all over the Eastern Sierra and across many awsome Colorado 4x4 trails (up to 13,000 ft and across boulder fields and beaver dams).

Here are a few examples of my TJ problem:
1. Going over a speed bump straight with constant speed (pushing on the accelerator to maintain speed): When I hit the bump at maybe 10 miles per hour the TJ learches forward then back and it seems like the gas pedal just kind of goes back and forth uncontrolled. THe engine jerks in response. The only way to avoid this is to coast over the speed bump with my foot off the gas pedal. Then the suspension handles the bump just fine.

2. In lo 4 I was able to go smoothly accelerating up a steep rutted hill but when I got to the top and tried to crawl over some deep ruts (straight on flat ground), the learching, jerking and bumping started again.  This time taking my foot off the pedal was not an option (or I would get stuck) so I just learched out trying the best I could to hold my foot even on the gas pedal (very difficult).

3. Driving slowly around a parking lot is not an option.  The TJ drives well if it is accelearting but not if trying to maintain a slow speed. I need to constantly alternate between putting in the clutch (coasting) and accelerating or the TJ will learch in response to slight gas pedal movements.

In hindsight, the two previous owners sold the TJ because the intended driver (a daughter in one case and a wife in the other) could not drive the stick shift.  My 16 year old son has a hard time with it too.  At first I thought it was something to get used to.  After going off road in lo 4, I know it is a problem that must be fixed.

If someone can explain the gas pedal to engine throtlle system, maybe I could figure out where the problem is. Maybe something in this system is loose or broken (a spring or tensioner, cable)?

[dunklervogel]

I have experienced this issue, although possibly not as extreme, with my TJ.  Because I didn't have a lot of experience driving a stick when I first started driving my Jeep I just assumed it was the "nature of the beast" to have this sort of thing happen.

Usually when the vehicle starts "kicking" I either give it some gas or press the clutch and that fixes it.

[(O|||||O) in SB]

I have experienced this issue, although possibly not as extreme, with my TJ. Because I didn't have a lot of experience driving a stick when I first started driving my Jeep I just assumed it was the "nature of the beast" to have this sort of thing happen.

Usually when the vehicle starts "kicking" I either give it some gas or press the clutch and that fixes it.

OK. This makes me even more determined to find a solution.

Have you re-geared?  It looks like you have a similar situation (stock 4 banger, 30/31 inch tires and no regearing).  Do you take your jeep off-road much? On rocky, steep trails? I have to get this problem fixed so I can go off-road!

There has to be a solution out there.

[Jeffy]

Tell us more about your Jeep.  Is it lifted?

What it sounds like to me is what is known as 'Death Wobble'.

[(O|||||O) in SB]

The TJ is not lifted - all stock except for 31 inch tires.

I understood Death Wobble happened when the TJ hits a bump going about 30 mph and the vehicle started to shake uncontrolably.  It has to do with the suspension being out of tune.

This is related to the gas pedal - not the suspension.  If I coast over a bump at the same speed there is no problem.

[Jeffy]

So you're seasawing?

[dunklervogel]

I haven't regeared and don't have a lift.
When I go offroad it is normally in wooded areas (I live in southern Ohio) but I have been through a few rocky trails around here and understand why you're asking.  I do remember the extra bumps and jolts causing it to act up more.
But after dealing with it for so long I have just gotten used to it... for the longest time I thought it was just the way a stick Jeep was.  I can coast over anything just fine this happens sometimes when I am either idling over a bump or slightly giving it some gas, I just compensate for it by giving it more gas or putting in the clutch.

[Bounty Hunter]

It's common, my YJ does it when you have too much foot on the pedal.  Back your foot of the gas pedal to where you're just using your toes to operate the accelerator.  You will no longer have the weight of your foot on the pedal and it won't bounce over the rough stuff.

Pretty funny hearing the mention of bumpsteer and DW

[SMC4WD]

My YJ has a 'sticky throttle'.  I hate it!!  It comes and goes...  but giving gas sometimes isn't a smooth operation.  If I maintain one steady speed, if I try to accelerate from there it's sticky.  It takes a second for the gas pedal to move, and when it does, it jerks...

I figured the I need to run lube down the throttle linkage cable and make sure that there are no binds in the line.  


Could that be your problem?

[(O|||||O) in SB]

I think I am getting closer to the problem.  Thank you for your ideas.

Today as I was driving I noticed that when I let my foot off the gas completely and then put it on slightly, the jerking happens.  I am now thinking maybe there is some slack in the throttle cable when it is all the way out and/or it sticks.

Does anyone have experience with throttle cable adjustments and lubrication? I don't want to put the wrong lube down the cable.

[(O|||||O) in SB]

I went to a jeep mechanic in Santa Barbara today.  As I started explaining the problem he knew exactly what I was talking about.  He called it bucking.  He said it is a common problem in TJs.

I set up an appointment to see what he can do.  He said he has had success dealing with it by adding a spring.

I'll let you know if the spring is successful in reducing the problem.

[Jeffy]

Hmm, interesting.  I'm assuming the spring is to hold the throttle cable or maybe adding one to the TB.  I'd really like to hear if it works and what he did.

 :cry:  Bounty didn't like my DW idea...  

[Bounty Hunter]

Likely an extra spring on the TB throttle linkage making for a stiffer accelerator pedal.