# Bucks at 2000 RPM



## NelsonCnty (Jan 7, 2008)

Hi y'all, long-time no problems 

...but recently, my '95 hb has been idling rough and bucks at around 2k rpm. there have been no error codes, and this has persisted through a few tanks og gas. 

I'm about to change the fuel filter (it's due), but I'm wondering if anyone has any other leads for me.

Thanks!


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## SPEEDO (Jun 9, 2003)

sounds like it is in "fail safe"
for me, it was a injector


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## NelsonCnty (Jan 7, 2008)

What's "fail safe," and how did you learn that it was an injector?

Were you having similar symptoms?


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## NelsonCnty (Jan 7, 2008)

The truck drives normally at RPMs above the 2,000 - 2,200 range. It's just if I'm cruising at low RPMs that it bucks, and as I mentioned, it idles rough.


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## smj999smj (Jan 1, 2006)

Could be an injector....could be worn or incorrect spark plugs, bad ignition wire, sticking EGR valve, bad distributor cap or moisture inside of it, intake manifold gasket or throttle body gasket leak. 95 KA24E's also had some problems with a splice on shared ground for the throttle sensor, exhaust gas temp sensor and engine temp sensor (refer NTB94-106). I've also seen fuel injector wires short out on the edge of the cylinder head.


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## NelsonCnty (Jan 7, 2008)

Sounds like it could be a lot of things, heh. Thanks for the list, smj. I'll just start cleaning and looking, testing what I can.


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## tomit (Jul 2, 2004)

I'd look at the EGR system.

Tom


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## SPEEDO (Jun 9, 2003)

NelsonCnty said:


> The truck drives normally at RPMs above the 2,000 - 2,200 range. It's just if I'm cruising at low RPMs that it bucks, and as I mentioned, it idles rough.


when it goes into fail safe, the rpms will not go higher... so I miss understood you..


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## zanegrey (Dec 5, 2005)

try removing the battery post for 5 to 10 minutes ..

then start trcuk and let warm up .. turn truck off and re read codes.. do not rely on cel check the codes...


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## NelsonCnty (Jan 7, 2008)

zanegrey - are you saying that I should check for codes even if the "check engine" light hasn't come on?

I'll add that it doesn't always buck/idle-poorly. This morning it was fine when I drove it, but I expect the bucking to happen later today when I take it out again...


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## zanegrey (Dec 5, 2005)

yes.......


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## jay5499 (Mar 13, 2012)

try cleaning the mass air flow sensor. use a can of mass air flow cleaner. be carful not to touch the little wires on it as it is pretty pricy to replace. my truck had the same issues and i cleaned it and runs good. i have a 95 4cyl. 4x4.


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## TheRepairMan (Jun 30, 2009)

jay5499 said:


> try cleaning the mass air flow sensor. use a can of mass air flow cleaner. be carful not to touch the little wires on it as it is pretty pricy to replace. my truck had the same issues and i cleaned it and runs good. i have a 95 4cyl. 4x4.


I think that's a good idea... trying to clean the MAF sensor, but do they actually make a special cleaner for that? I thought just using electrical contact cleaner worked okay.

-R


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## TheRepairMan (Jun 30, 2009)

TheRepairMan said:


> I think that's a good idea... trying to clean the MAF sensor, but do they actually make a special cleaner for that? I thought just using electrical contact cleaner worked okay.
> 
> -R


I had to run through a parts store yesterday after work, and yes, CRC actually does make a "Mass Air Flow Sensor" cleaner! There may be other brands out there as well, but nobody had told me about any of them.

Honestly, our shop has just been following car manufacturer procedure of testing and replacing them, but I've known for quite a while that most of them were not bad enough to even cause the CEL to come on. So, the cars often run horrible, usually way too rich, and no clue about what the problem might be. Keep in mind there are a few things besides the MAF that can make one run rich. Commonly on some cars, the coolant temperature sensor, and/or a bad fuel pressure regulator.

On 96 and up cars the fuel trim numbers would be just outside of normal range, and did have a CEL lit, but everything else in the ignition and fueling checked out to be working okay. These vehicles might have easily been restored to normal, and leaned back out by a good cleaning of the MAF. It would have been worth a try, so I'm keeping that in mind for the next ones that come in rather than just throwing a new MAF at them. $8 for cleaner and just a little time, versus hundreds for a MAF is a no brainer.

Now... how often should this be done on our trucks as a preventative maintenance service item?

-R


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## NelsonCnty (Jan 7, 2008)

I cleaned the MAF with the recommended cleaner, and repaired a broken wire at the air temp sensor (for the 3rd time in 4 years), but that didn't seem to help. I replaced the fuel filter - truck is running *much* better now, but not completely back to normal. So this morning I put a bottle of injector cleaner and filled the tank with premium, hopefully that'll get some more of the gunk out of the fuel system.


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