2000 S10 LS 4wd, 4.3L vortec, 156K miles....I am having an intermittent excessive engine rpm issue....when it occurs happens cold or warm, and again, only intermittantly-no rhyme or reason..when it happens warm is when I come to a stop @ a stop sign or a light or put the tranny in neutral to coast downhill to try n save some gas, my rpms will hover btwn 1700-2100 rpms-WAYYY too high...again, doesnt happen every time, just randomly...if I let the truck sit there, in park or neutral, it will continue for a min or 3 and FINALLY settle back down to a normal rpm of 700 or so. the only code my ODB II tool will find, even when attaching the tool live during the issue, and again, it doesnt throw this code every time the condition exits, is a P306, which is a #6 cylinder misfire...I have replaced the cap, rotor, all plug wires and plugs, even rechecked later that maybe I didnt have a plug wire boot on correctly @ either the cap or the plug, Has not since thrown this code after I did that.Throttle position sensor, maf sensor, map sensor,egr valve replaced, checked for any vacuum leaks around the throttle body area by starting fdluid method and the air filter assy was correctly buttoned down..I've even checked both throttle cables and the throttle body springs while the condition is happening and nothing is hanging up or stuck and have run 2 bottles of the Red Heet thru the fuel system..oh..and the fuel pump was replaced about 1,000 miles ago....thoughts or advice, short of payin a mech w/a 15,000 dollar machine (which I am willing to do, should I get no helpful advice) to find this darn Gremlin?...thanks

 

bumping the thread

 

what?...no ideas?...bumping again

 

You probably have a vac leaks. Mine is 4 cyl, and there is a hose over on top of the engine wich is very brittle. That hose was cracked. I replaced it with new one and now no high rev.

 

was hoping spraying starter fluid would have verified a vac leak, tho...there is such a "rat's nest of various vac hose all OVER this v6...'lil 4 bangers prob can see and spot vac easier...thanks tho

 

High rpm's to me is vaccum leak. Your truck is 20 years old, my suggestion is start with vacuum hose's, as in replacing them.

 

can any one furnish a COMPLETE list of engine bay vac hoses and their associated routings?

 

I am happy to report I've finally run down the cause of this issue...thanks to Maz Village and kevinkpk...altho I thought I had eliminated all possible vac. leaks, I never gave any thought to the throttle body base gasket..I had sprayed start fluid all around that base and heard no change in engine speed, so I dismissed that. Came across a YouTube that said a defective throttle body base gasket can cause an intermittent hi idle issue...Apparently, the gasket would seal when engine was warm/hot, but musta been weak when engine was cold...causing the engine to roar @ 2200 RPM's...I had already thrown about every part known to man related to air and fuel under the hood, but figured WTH, a base gasket is $3....and the assy is easily removable...intensively cleaned the throttle body while I had it off as well, removing both sensors before cleaning and cleaning their ports too...cold starts she purrs like a kitten now-about 1000 rpms, backing back to the normal 700-800 once warmed up, other than I now have a damn engine knock from the many hi revs over past 3+ months...time fer another truck.