Engine tremble?

[Chevyc10]

 I just bought a 01' Siverado LS.  Its a dream come true...  except for the motor.  I have the 4800 in it.  The problem is that the motor has a slight miss or something that is noticeable at idle.  I took it back to the dealer and of course " they all do it" he said.  I insisted that he prove this, and we took a ride in another truck and sure enough it did it as well.  Not as pronounced as mine though.  He called it a slight "tremble" at idle that is caused by a lean condition at idle.  This sounds like complete B.S. to me.  My 68 purs like a kitten never skips a beat.  Anyone else out there notice this on your trucks (99-01)?  Seems to me that by the year 2001 they could make an engine run a #### of a lot smoother than that!

[Frank S]

First off,welcome to the site!

Senondly,from my expierences with the fuel injected GM trucks,your dealer is telling the truth,they ALL do it.

I have a 2001 Silverado work truck with the 4.8,my youngest brother has a 2000 Z71 5.3,the wife's 5.7 '99 Tahoe and my mothers '99 5.7 Suburban all have the same "idle hesitation" that you are describing.My tbi '93 did the same thing as well so it's probably something that you'll just have to deal with.

[Shaners]

My '00 will wiggle the tip of the antenna at a stop light.  It idles at a pretty low RPM when in gear and that may be part of the problem...  It doesn't show any stumble or hesitation when I step on the gas though, (if it did I would be very concerned).

[Shaners]

By the way...  welcome!!!

I wanted to let you know a friend of mine just bought a used '99 Z71 excab with the 4.8L and his first tank of fuel netted 18.5mpg!!!  The truck has 45,000 miles on it!!!  (I'll ask him at work this week if his truck shows any of the same signs as yours)

[76BBSub]

This is a common problem with the Vortec engines, dating all the way back to '96 when they were introduced.  You see...in order to minimize hydrocarbon emissions and maximize fuel economy they have these trucks dialed in pretty lean, and the idle is VERY low when compared to older trucks.  This results in a bit of a miss at idle, although some trucks are worse than others.  My '96 was pretty bad.  I tried several times to get the dealer to reprogram the PCM to fix it, they kept saying it was out of warranty.  Well, you guys are gonna love this one.  About 1000 miles after the warranty ran out the O2 sensor died on me.  Took it to the SAME dealer I bought the truck from, which was the same dealer I had been pestering about this problem for more than a year.  What did they say...the O2 sensor was bad AND for ? they needed to reprogram the PCM!!!  I hit the ROOF!  I got them to replace the O2 sensor for the cost of the part, but they never would admit that the PCM really needed to be reprogrammed, nor would they do it for me.  This is such BS.  Anyway...

I _think_ that if you bought a HyperTech power programmer that you could fatten up the fuel curve to include idle, and lose some of that miss.  Otherwise, you'll have to live with it.

I find a certain satisfaction in the fact that my '76 Sub 454 idles smoother than my '96 GMC Vortec ever did.

Jeff

[MattH]

yeah, the pcm update for the 96 and 97s helped out quite a bit with drivability issues.  the dealer should have done that.

as far as the hypertech goes, they cannot change anything that goes on in closed loop, therefore cannot do anything to the fuel control at idle.

besides, with fuel prices the way they are, i would love to have that lean idle to help me get better mileage.