Occasionally this past winter when I would start my Envoy, about a second after the engine turned over, the RPM's would suddenly drop down to 2-3k before shooting back up to normal engine warm-up levels and eventually settling down at normal. The engine never stalled, but sure as hell seemed like it would. 115k miles, spark plugs were changed and throttle body cleaned this past summer with no issues after. No codes. I initially thought it had to do with extreme cold, but even on some of the milder days over the winter it happened. No rhyme or reason that I can see yet. Any ideas? Maybe the MAF sensor?
RPM drop then recovery at start
- Thread starter breckbrew
- Start date
Wooluf1952
Member
Welcome In case you haven't heard:
http://gmtnation.com/forums/topic/218-welcome-to-gmtnationcom-heres-the-story/
Did you mean it would drop down to 2-3 hundred on the tach? Mine never gets to 2k at start-up even on the coldest days.
However, does the falling RPS's coincide with the sound of a vacuum cleaner? My mind is blanking right now and I can't remember the name' sorry. SAIS (Secondary Air Injection System), maybe? Others will jump in.
SnowBlazer
Member
My rig does that normally when temps are below 30F. Mine will start, and run week for a few seconds, then catch its self and run like normal.
kickass audio
Member
- Joined
- Aug 25, 2012
- Posts
- 955
question for you, when this happens, did you notice if the volt meter shows down around the 12v mark or is it up past the 14v mark a little? Mine usually when its cold, it gets up to around 1800-2000 rpm when the SAIS pump is on and the alt is off, when the alt kicks on, it gets to 1700 and then back up to 1800 for a bit until the SAIS turns off and it gets down to around 1200-1000. If you want, try to take off your belt and start the truck when the engine is cold (do not run the truck without the belt on for a long period of time) see if your RPM drop is present. If it isn't then that would lead me to think something on the belt drive is bogging down the engine.
This is highly frowned upon but I do it when I clean my throttle body and take it off the truck and have 0 issues, I clean up the throttle body and push the plate in like you are closing it off completely and see if it sticks. If it has any bit of sticking or is harder to push closed (push gently of course) then it may be a bad gear or more crap built up in the throttle body that is jamming it when it goes through its initial sweep when you turn the truck on. Another thing to try, take off the intake assembly and watch the throttle body open and close when you turn the ignition to the run position (do not start it). You should see it close itself up and then open up a little to its idle position. If you see it close and hesitate to re-open, you have a sticking throttle body.
edit: NEVER push with a lot of force on the throttle plate or push on it with the electrical connector hooked up, you can break the throttle body doing that.
This is highly frowned upon but I do it when I clean my throttle body and take it off the truck and have 0 issues, I clean up the throttle body and push the plate in like you are closing it off completely and see if it sticks. If it has any bit of sticking or is harder to push closed (push gently of course) then it may be a bad gear or more crap built up in the throttle body that is jamming it when it goes through its initial sweep when you turn the truck on. Another thing to try, take off the intake assembly and watch the throttle body open and close when you turn the ignition to the run position (do not start it). You should see it close itself up and then open up a little to its idle position. If you see it close and hesitate to re-open, you have a sticking throttle body.
edit: NEVER push with a lot of force on the throttle plate or push on it with the electrical connector hooked up, you can break the throttle body doing that.
I keep telling myself that I need to look at the voltmeter when it happens, but I haven't yet. I thought I cleaned the throttle body pretty good, but maybe I'll take a look at that again to see if it is sticking. On one hand, I hope that its just a cold weather fluke and that it won't happen again until next November, but on the other hand, I hope it keeps happening so I can figure out what it is.
Thanks!
Thanks!
