searched this forum, but wasnt able to find my particular issue...2000LS, automatic, 4WD, 4.3 Vortec, apprx 135k on motor, 160k on tranny......most times on cold start, goes to 1200 or so rpms for 10-30 seconds or so, then slowly drifts back to proper 600 or rpms...but sometimes, as SOON as I put the truck into D OR R, the rpms fly to at least 1500..also does this randomly even when engine is warmed up...if I let the truck roll in D or R and put tranny in N while rolling, the rpms really jump....this issue usually goes away after 15 mins of driving, but I gotta keep my foot @ the ready cuz the trucks wants to GO...afterwards, once warmed up, it starts to behave "normal" again, but sometimes if I were to say, be going downhill and put 'er in N to coast, it STILL will sometime jump to 1200-1500....then even when the truck DOES go to normal 600 or so while coasting, once i put 'er BACK into a gear, the engine always wants to add 500 or so rpms even tho I aint touchin the foot pedal...aggravatin'!!! when I come to a stop, THEN the engine rpms behave correctly, in N but still wants to do about 500rpms more if I leave it in D and then drifts down to the proper 600 or so in about 5-10 seconds...I've replaced the TPS and IAC...and I have no CEL or any detected or pending codes w/my OBDII tool, doesnt seem to be any binding or hangup on both cables going to the throttle body or the return spring, tranny shifts smoothly both manually and automatically and cannot detect any kind of tranny slippage on acceleration/deceleration,making me think this is a sensor/PCM communication issue, not a possible tranny failure/issue.....thoughts and possible places to look?

 

Sounds like a potentially dangerous mistake to drive your vehicle, if it speeds up when it should not. It might be costly, but it could be a Bad ECM/PTM.

 

not like it really wants to "hole shot"-I can easily keep 'er reigned in..like I said, this is a random issue w/no rhyme or reason, but is ruining the already **** POOR gas mileage of 4WD V6 S10's

 

The 4.3 is not really an economy motor. The 5.7 is better than the 4.3 L by a country mile, IMHO. All 4WD don't do well on gas mileage.no matter the engine.

 

yeah..4.3 was as big as ya could get in an S10...and, as SHOEHORNED as the 4.3 is in that engine bay, I dont think even a CHEVY engineer could fit anything bigger in 'er, thank GOD...anyhoo..hope someone reads this thread that can point me to some logical places to look

 

..bumping..

 

Based on your follow-up comments, this all sounds like normal RPM ranges. 2,000 RPMs right at startup is normal, just as long as it goes back down after a few seconds or so. (it may stay higher for longer when it’s really cold out).

As for shifting into Drive, the RPMs will slightly go down because the engine connects to the transmission, and the resistance of the transmission fluid takes energy from the engine and lowers the idle speed slightly. Vice versa, when shifting into Park, the RPMs will go up temporarily because that resistance is no longer there. Your car’s computer will notice this and bring the idle RPMs back down to the normal 800-900 RPMs.

 

I have seen V8's shoved into cars way back when, even a Chevy Vega and the Fix-Or-Repair Daily Pintos, but not without cutting away at the sheet metal. Bet lots of those chumps blew out the rear axle fast unless they put a stronger axle in its place. Back in the day you could do stuff like that, but these cars were not designed for a V8 motor. Neither were the brakes, drums, designed for all that extra weight.Crazy stuff!

 

chevyboy...
I totally agree w/your asessment of normal cold operation...however, when this random issue rears its ugly, it is far MORE than a "few seconds"....if I dont do anything, even after 30 seconds and more, the rpms will even start to climb above 1500- even if I rev n pump the pedal-I have to get it in gear n' GET goin, then she'll calm down after a few miles of driving MOST of the time...also, I've had this random issue crop up AFTER a good 30-40 mins of driving...no excuse that the engine aint warm by then!...and 3rdly, when coasting downhill in N, I dont see how ANY "resistance" or "call for increase engine rpms" is needed by an auto transmission....it should fall back to normal idle rpms....the only time while this issue is occuring that the rpms will return to idle rpm is if I bring the truck to a COMPLETE stop...even if the truck is rolling in N at a snail's pace, the rpms stick around 1500 UNTIL I come to a FULL stop...why I say something's amiss...as I stated in my orig post, I've thrown new IAC and TPS sensors at this, tryin to resolve-is it possible I got 1 or the other, or both defective outta da box from Rock Auto?

 

bumpin' this thread