Engine/Transmission (1998.5 - 2002) idle fluctuation and truck rocking

[JCyrbok]

My idle has had a flucuation to it since I got my truck new. The way I understand it is that it is normal, do to the way the ECM constantly updates timing.



However just recently when my truck is first started in morning or after several hours sitting the flucuation actually causes my truck to slightly rock side to side.



The actual flucuation of the RPM does not seem to be any more than usual, but I can hear it ( when i used to not beable to) and the truck rocks. It does not do it when in drive or any other gear, there is no surging in gear and does not do it if warmed up.



ANy idea's?



Thanks

J-

 

[andrewkoperdak]

Crankshaft position sensor faulty?

 

[JCyrbok]

Thats kinda what I was thinking. Is there any way to know for sure. Will it set a code? Is there a way I can test it or just the dealer with the fancy computer?



Thanks

J-

 

[andrewkoperdak]

It may set a code, there is one for that but, but I have yet to see one. I had a problem some time back where my idle was loping by about 300 RPM and it never set a code. Problem happened twice that year and never since. Outside temps were extreme like 111 degree so maybe my HP fuel pump was getting hot. Who knows... ... . never a code though.

Dealers pretty much can only find a problem that jumps out and catches there attention. I would not rely on them to fix your problem. I haven't had to replace my C. P. S. so I don't know if it is envolved or not. I would tackle it though because you would know for sure if it fixed the problem or not.

R,

Andy

 

[jmtandem]

slight idle variation

Mine experiences a slight idle fluctuation of about plus or minus 25 rpm's (less than the tach needle width). It is a little rougher when the A/C is on , the heater grids cycle in the morning or the fan is working on a hot day at idle. It can cause the gear shift (5 speed manual) lever to slightly rock sideways. If the fuel filter needs changing it shows up in a little rougher idle. I have been told that slight idle fluctuations are normal as the computer is compensating several times a second. What is perplexing is that there are times when the truck idles absolutely perfect and the tach needle is rock steady. Mostly these occur after a long down grade of several miles with the throttle closed (6-7 percent grade) and for some time after even in stop and go traffic.

 

[JCyrbok]

Yeah my tach has always had that slight bounce to it too and was told that it was normal. It is just in the past 3 weeks that the bounce is accompanied by a slight rythmic rocking. It is only after it has sat over night or while I'm at work, never while it is warmed up. I changed my Fuel Filter about 1k ago and that filter was clean.



Thanks for any help

J-