slow engine deceleration when shifting between gears. any way to stop this from happening?

claytonbretveld
5

Asked by claytonbretveld Feb 21, 2013 at 08:57 PM about the 1998 GMC Sierra 1500 K1500 SLE 4WD Standard Cab SB

Question type: Car Customization

i have a 98 gmc sierra 5.7 5 speed. when i push in the clutch and go to shift to the next gear the rpm hangs there for a few seconds and im sure it has something to do with smooth shifting but it bugs me because im used to driving non electronic vehicles. also if i leave it in gear and clutch still engauged when i let off the gas it takes about five seconds before the engine actually starts to decelerate. is there any way to make the engine rpm drop as soon as i let off?

8 Answers

tenspeed
61,185

There's a dash-pot type of affair that keeps the throttle plate from slamming shut. The slow closing throttle burns the fuel mixture cleaner. I've noticed it too with my manual tranny vehicles.

claytonbretveld
5

well if you rev it up in neutral it drops like it should but if its in gear it has that funny lag before it starts dropping. so i just wondered if i could change that somehow

7jimmy7
13,045

their is a switch under dash that tells the pcm clutch angle ,connected to lever arm,remove and clean or replace,maby cure rev issue

Alex Nazarian
885

Possible vac leak, tps or iac issue. Check your DTCs and report back.

claytonbretveld
5

all systems are good no codes or leaks. ive driven a few of these trucks and they all do the same thing so i think its supposed to do it but i dont want it to.

Michael Tutty
5,265

They are designed to do this as part of the emissions control system. It is, in my opinion, plain dangerous in certain circumstances. There is an aftermarket attachment that can be fitted that does away with the throttle lag. I makes a huge difference to throttle response both when you add and when you release. Any good performance shop should be able to steer you in the right direction. Failing that, check LMC.

claytonbretveld
5

do you know what the part is called? cant seem to find anything

Andrew Olsen
7,945

I've driven a few of 5 speed chevy's and they all have done this. The 5 speed trans in these trucks isnt designed to be quick shifted, It normally holds rpm's up after clutch release for only 1 sec. It's normal operation and will only be a problem if you try to float gears or something. It's not a throttle lag as if still in gear it should still decelerate as soon as you let off the pedal. If it doesnt then i'd worry about it. Also when cold it will have a high idle and magnify the effects of this system.

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