# slight bucking, low idle



## NelsonCnty (Jan 7, 2008)

mornin' -

so yesterday afternoon, I felt a bit of "bucking" in first gear, as if I wasn't giving it enough gas. it did this a few other times that afternoon along my 30-mile drive, in other gears as well. also, it was idling very low for a bit and the check engine light came on, briefly.

it got me thinking (because I'm a worst-case scenario kind of guy) about the timing chain and how I'm the 4th owner of this truck (206,000 miles) and I don't know if the chain has ever been serviced.

I know this sort of behavior is typical of low fuel pressure or an air/vac problem, but is this also the type of behavior that could indicate a chain that's about to fail?

I called my mechanic and asked when timing chains should be serviced and he said "when they start making noise." I don't think mine makes any noise. Sometimes right when the truck starts and does it's initial revving, there's something of a scraping sound but nothing major (may be normal, I don't know).

Anyway, should I change this chain purely for maintainance, or do ya'll actually wait for a warning?

I should mention: '96, 2wd, 4cyl

Thanks!


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## lumbee (Mar 20, 2005)

...bit of a debate on when/if the timing chain should be changed. If you do a search on it, you can read both sides of it. The earlier models had plastic cam chain guides, but u'rs should have metal guides, and should not need changing. Either way I don't think u'r symptoms have anything to do with the timing chain. This should be an easy diagnosis since the check engine light came on. Go to u'r local autoparts store and have them read the codes. Could be O2 sensor which is a common problem. Anyway, get the code read, and report back...


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## NelsonCnty (Jan 7, 2008)

thanks Lumbee,

yeah, I read some of that healthy debate here about that 

the check engine light came on only briefly. am I correct to assume that this code is still stored in the box? if so, I'll pop the seat out and read it tonight.


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## NelsonCnty (Jan 7, 2008)

okay:

the code read out was 43: Throttle sensor. 

the book says that the throttle sensor circuit is open or shorted and this fix must be performed by a dealer or shop. is this really the case? what can I look at here?

this bucking happened again yesterday afternoon. seems to happen after it has warmed up outside.

thanks!


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## lumbee (Mar 20, 2005)

...no experience with that...maybe someone else will chime in...do a search and see what comes up...


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## rdixiemiller (Mar 6, 2008)

I wouldn't worry about the timing chain. I hit a deer with my '93 when it had 220k miles on it. Since I had the radiator out and the hood off, I decided to do the timing chain. It was fine! I replaced it anyway, since I was already in there, but everything looked good.


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## NicHB (Mar 5, 2008)

I'm having the same bucking problem with my 95 HB but I'm not getting a code. I haven't had any luck finding the problem yet.


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## NelsonCnty (Jan 7, 2008)

the problem seems to have subsided lately. I noticed a few days ago when I went to fill up on gas that the cap was loose. we also had a couple of rainy days...so I'm thinking maybe some water or air got in the system. I put some gas treatment in with the next fill up and made sure the cap was on correctly (duh). hopefully, this does the trick.


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## NelsonCnty (Jan 7, 2008)

okay, I take it back...it's still doing it.

by the way, it's a 95, not a 96 like I originally said.

so nobody has any idea about the "throttle sensor" error code 43?


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## NicHB (Mar 5, 2008)

My truck bucks in all gears when I coast. I left off the pedal, it coasts a little then bucks down. When I hit the gas again it buck back up. It's like there is some sort of threshold. I can make it do it every time.


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## NelsonCnty (Jan 7, 2008)

- truck bucks a little
- then it will idle very low at the next stop light
- check engine light comes on
- error code 43: throttle sensor

ideas?


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## rdixiemiller (Mar 6, 2008)

Not absolutely certain, but most FI engines use a Throttle Position Sensor. This is a variable potentiometer on the accelerator pedal that gives different resistance as the throttle is opened up. There is actually no mechanical connection to the FI unit, just electrical signals.
So, call a dealer and see what one costs. It may be reasonable. You may want to hit a U-Pull-It yard and get one cheap.


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## caferacer82 (Apr 21, 2008)

Ive got the same problem in my 97. Took the time to change out my plugs, wires, distributor cap and rotor this weekend, didnt make a dang difference.


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## caferacer82 (Apr 21, 2008)

Changed my fuel filter last night and gravy came out, bucking seems to be gone. Its not to hard, just take off the air cleaner housing and be sure and use a puralator brand


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## NicHB (Mar 5, 2008)

I still have the problem but I'll share some narrowed down symptoms. 

First, it only starts "bucking" after the engine has reached it highest operating temp.

Second, I have found I can make it go away for a while by pushing in the clutch and rev the engine to about 5000 rpm. I'm not sure this is a good thing but it's what I know works for now.

I keep thinking it might be a vacuum leak but I can't find anything. Do gas caps go bad an cause problems. I bought a replacement about 6 years ago that locks with a key.


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## saidiadude (Mar 31, 2008)

If you think it's a vacuum leak, spray carb cleaner on the vac hoses while the truck is running. If the RPMs change, you've got a vac leak. Be careful! Don't spray the cleaner on hot areas!


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## Best of the Best (Jul 31, 2007)

95 HB with over 200k miles. Periodic bucking, idle dropped off. Changed plugs, wires, cap, rotor, fuel filter and air filter problem continued. My mechanic discovered broken wire on mass air flow modulator. Repaired the broken wire, problem solved. Check that sensor first before changing anything.


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## NicHB (Mar 5, 2008)

I read another thread on here about cleaning the MAF sensor. I hope this helps. Stay tuned...


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## NelsonCnty (Jan 7, 2008)

thanks everyone for your tips! I'll let you know if/when I figure it out.

for the record, it hasn't done this in a month or more.


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## cjserio (Mar 18, 2008)

As someone else mentioned, be sure to check your throttle position sensor. On the KA24E it's bolted to the front of the throttle body and held there with 2 screws. Mine just died today and my check engine light came on. I'm anxious to swap it out tomorrow and see if it solves some of the bucking problems i've been having.


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## NelsonCnty (Jan 7, 2008)

I'm not sure what the throttle sensor looks like - is it in the haynes manual?

Same goes for the air flow sensor. I found the section (paragraph) that talks about it, but where is it and what does it look like? Any tips on how to clean/check it?

Thanks!


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## cjserio (Mar 18, 2008)

NelsonCty, go back a page or two in the forum history. I wrote a quick blurb about how to clean it and find it on a KA24E. It's very simple...just be careful not to damage it as it's very fragile.


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## NelsonCnty (Jan 7, 2008)

awesome man, thank you!


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## cjserio (Mar 18, 2008)

The throttle sensor is bolted to the front side of the Throttle Body on the KA24E. There's no way of cleaning it but you can check it by measuring it's resistance as you step on the gas. It should vary from 500ohms to 4,000ohms.


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## boosthappy (May 15, 2008)

*change TPS*



NelsonCnty said:


> - truck bucks a little
> - then it will idle very low at the next stop light
> - check engine light comes on
> - error code 43: throttle sensor
> ...


ok dude check this right........my sr20det motor did the same thing your car is doing and i got a code for a TPS sensor, after i change it the car was fine...the way the tps sensor works is by voltage [email protected] idle and 5.0 volts when you put the gas to the floor and lets say you have a bad tps thats a problem because let's say your cruzing around and your at about %20 throttle the tps reads 1.50 volts So.....it sends that info to the ecu so the ecu can tell what load point the motor is at so it can adjust fuel and timing according to the amount of throttle you give it get it....... so if the voltage is off the ecu never gets the right reading and there for puts the wrong amount of fuel and timing get it......


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## Best of the Best (Jul 31, 2007)

Guys, guys check the wires going to the mass air flow sensor. My 95 KA24E HB did the same thing, intermittant bucking, erratic idle. Check those wires. The wires on my Intake Air Temp sensor also came loose.

Flow sensor is in the throttle body and the temp sensor is on the under side of the air filter housing.

Good Luck


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## NelsonCnty (Jan 7, 2008)

yeah, the first time the check engine light came on, it was the air temp sensor under the air cleaner housing...a wire was disconnected, so I soldered it back in place.

will definitely check the things listed above. haven't had a minute yet, but should tonight or tomorrow.


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## christinefenton (May 12, 2008)

Not sure if this is the problem, but I own a 2001 Nissan Pathfinder & just recently had similar issues. Although mine worked fine in other gears..just upon first acceleration to within a block. Hesitating/surging...sometimes felt like it was about to stall. I had to replace all three camshaft sensors. Just a suggestion....I'm still learning.....


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## bobt2382 (Oct 17, 2005)

I own a CA emission 97 HB, 2.4L. Mine started doing the same. Upon statup, It would idle correctly for about 3-5 seconds and then start to bog as the idle dropped. It would stall unless I depressed the gas pedal where it would start to bog.

I thought I had water in the gas tank so I added an additive to absorb the water. The next day I disconnected the Mass Air Flow (MAF) sensor connector and low and behold, i would idle correctly. As I rev'ed the engine it would start to stutter and bog above 2500 RPM. I figured I was in the correct area. I removed the MAF sensor and carefully cleaned both small MAF wires with alocohol and a cotton swab as decribed in earlier posts. By the way, the MAF on this motor only has two screws. I reconnected and restarted the engine. It idled well and I was able to drive without any issues. I drove 200 plus miles. 

The next day, I was a little "depressed" when I started the engine. It had very similar symptoms...would idle for 3-5 seconds and then start to lose RPM. The only difference is that it did not stall.

As I removed the air cleaner top portion, it appeared to idle correctly! I placed the top protion of the air cleaner, and yes you guessed correctly, the idle began to drop. I then remembered, that I remvoed my K&N filter a few weeks before and used an '''old" air filter. I placed the "dirty" K&N filter and the top of the air cleaner!

Truck runs better after a week!

1. Truck has 240K and all original sensors. I replaced bothe fron and rear O2 sensors at 200K. I never had the MIL (check engine light) indicate that there was a problem with O2 sensors.

2. Original MAF was cleaned. Please do that. Disconnect the connector and see if it idles and starts to bog/stall at approximately 2500 and above RPM.

3. I may have had (or still have) moisture in the gas tank. A few bottles of additive cost less than $5. Probably worth it. It is difficult tell if you have water in the tank. I did not check my fuel line pressure! I will for peace of mind in the very near future. I have a 8 micron K&N fuel filter that I had bought back in 1997, shortly after ourchasing the truck. I had cleaned the filter element the same day I placed the "old" filter in, so I was fairly certain that the filter was not the problem. 

4. I believe that the "old" air filter was part of the problem along with a dirty MAF sensor. I had an old FRAM and was not really impressed with their quality to begin with. Please check/replace with a quality air filter.

Hope this may help someone with similar problems.


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## NicHB (Mar 5, 2008)

ok, here we go. I got it fixed.

First, I read the codes and got a air temp. sensor code so I replaced it an cleared the codes. The check engine light went off but the bucking still happened once the truck warmed up. It was idling very strange going from ~600rpm to over 1000 randomly while idling and after the engine was warm. 

I now noticed that the CEL would come on then off as the bucking started. So I pull the seat and check the codes again and nothing. Apparently it wasn't storing the code.

I do the carb spray trick and find a few small vacuum leaks on the emission stuff so I replace about 4-5ft of vacuum hose. The bucking keeps happening. 

Finally I figure out how to trick the truck into keeping the CEL on. I get the truck warm and make it buck by down shifting from 4th the second after the motor has been idling around 600rpm (it took a while to figure this out and it really didn't always work. I probably just got lucky).

Anyway, I pull in the driveway and turn the truck off with the CEL still on, pull the seat, and read the code. Guess what... Throttle position sensor code. I buy the stupid $68 part (californina model), pull the 2 breass screws (make sure you tap them with a hammer and screw driver to loosen them) and replace the silly plastic part and VOILA... it runs perfect now.:woowoo:


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## dvdswanson (Nov 6, 2005)

TPS should have voltage of .6 - .8 vdc if I remember right. check your PMs


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## NelsonCnty (Jan 7, 2008)

will I need to callibrate a new TPS that I buy from an auto parts store?


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## cjserio (Mar 18, 2008)

There are no calibrations on the sensor...There is an adjustment in how you mount it. There are mounting grooves not holes so that you can twist the sensor slightly. When you mount it, you mount it such that you get 500 ohms with the throttle at Idle and 4k ohms with the throttle fully open. If you're not getting that range you can loosen the screws and rotate the sensor a bit until you do get it right.


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## cjserio (Mar 18, 2008)

Actually my numbers are valid for a KA24E engine only. I didn't notice which one you have.


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## NelsonCnty (Jan 7, 2008)

okay, new developments:

last night I measured 500 ohms with the TPS at rest and 4500 ohms with the pedal to the floor (ignition and engine off of course). I know this is a test of how well it is adjusted, but does this also mean that my TPS is still good? or, can a faulty TPS still respond correctly, in terms of resistance?

also, I cleaned my mass airflow sensor. not sure if it needed it or not, but I also do not know for sure if it had ever been cleaned.

a second problem too: recently, the engine has been sounding loud...like air. as if the truck had a really big fan on it that went faster as you accelerate. a wooshing as you take off. know what I mean? any ideas?

I read codes 32 "EGR control valve does not operate" and 43 "throttle sensor circuit is opened or shorted," though I hadn't reset the code in a month or two.

thanks for all your help so far!


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## zanegrey (Dec 5, 2005)

well ,
the wooshing is the fan clutch ..


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## NelsonCnty (Jan 7, 2008)

> the wooshing is the fan clutch


ah. how do you diagnose that (other than the wooshing over the internet  )? is it a tough job and is it something that must be done before I take the truck out of town this weekend?


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## zanegrey (Dec 5, 2005)

do not attempt to look behind the curtain...

just repalce it...

you can drive it like that ..it will affect your gas mileage and cool the engine too much..

it also could be the problem you have been having to whole time..


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## NelsonCnty (Jan 7, 2008)

good to know - thank you!

so I guess what I still need to figure out is this:



> last night I measured 500 ohms with the TPS at rest and 4500 ohms with the pedal to the floor (ignition and engine off of course). I know this is a test of how well it is adjusted, but does this also mean that my TPS is still good? or, can a faulty TPS still respond correctly, in terms of resistance?


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## zanegrey (Dec 5, 2005)

i think that you have your meter on the wrong setting..

how ever if it has an ohm range it is working..

replace the fan clutch and then warm engine up and re read codes


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## rogoman (Dec 16, 2004)

When cleaning the MAF, use only ELECTRICAL CONTACT CLEANER or a cleaner specifically made for MAF hot wire cleaning. This is the only thing you should use to clean your MAF. No windex, no carb cleaner, no brake cleaner, no rubbing alcohol, and no Q-Tips.


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## NelsonCnty (Jan 7, 2008)

hmm, well I used q-tips and rubbing alcohol, which is what I've seen recommended most if not all of the time 'round here and elsewhere. 

here's hopin'.


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## NelsonCnty (Jan 7, 2008)

well, a couple of weeks and abour 1400 miles later, all is well (with the TPS, at least). I have felt no kick-down at cruising speeds, and that particular error code has not returned.

I'm not sure it had to with unplugging/plugging in the wire to the TPS (because the sensor itself checked out okay) or if it had to do with cleaning the MAF, but so far so good!

Thanks, everyone, for your help.


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