hi , i have a strange issue that's a bit difficult to describe. first i have an 05 LS, 4.2, 175k miles. when i'm in a parking lot (slow speed), for example, and i let off the gas pedal to make a turn, the vehicle idle will sometimes surge, like i've i've tapped the pedal. it's very strange and i think it's dangerous in tight areas like a parking lot. anyone ever hear of this?
Idle Surge at Low Speed
- Thread starter jeff180
- Start date
Robbabob
Member
- Dec 10, 2012
- 1,096
i 've had the TB a little under 2 years. i have cleaned the throttle body twice; once when i first bought it (the engine would stall when the A/C was turned on. it was VERY dirty). the plugs were changed at 184k (my initial post should say 195k miles currently, not 175k - my mistake.)
Robbabob
Member
- Dec 10, 2012
- 1,096
I am still not seeing when was the last time you cleaned the throttle body. You've cleaned it twice, once when you first purchased the truck, but you didn't follow up with the timing on the second cleaning. Someone may chime in if there is an IAC to clean; I'm not so familiar with this area.
My guess is, the hydraulics in the steering are causing a dip in the RPM, from which the engine overcompensates. Again just guessing, if your TB is dirty, you are going to receive rough performance.
This is just the starting line for debugging, and many times will prove to be the solution.
At 200K miles:
My guess is, the hydraulics in the steering are causing a dip in the RPM, from which the engine overcompensates. Again just guessing, if your TB is dirty, you are going to receive rough performance.
This is just the starting line for debugging, and many times will prove to be the solution.
At 200K miles:
- Change the spark plugs
- Change the fluid in the front and rear differentials
- Change the Transfer Case fluid (If you are not familiar, it takes Auto Track II, not part of the transmission)
-bought the trailblazer at around 175k, gave the throttle body a very good cleaning (removed it and cleaned it)
-changed the plugs at 184k. gave the throttle body another once-over
i thought about the steering causing a dip. not sure where to start on that, but i will look in to changing the fluids as you described. i have no maintenance records for prior to my ownership, but i assume it hasn't been kept up (like i always assume with a new-to-me car), but i can tell it had been sittting for a long time. looks like all the OEM parts were still there or somebody changed them with Delco parts.
-changed the plugs at 184k. gave the throttle body another once-over
i thought about the steering causing a dip. not sure where to start on that, but i will look in to changing the fluids as you described. i have no maintenance records for prior to my ownership, but i assume it hasn't been kept up (like i always assume with a new-to-me car), but i can tell it had been sittting for a long time. looks like all the OEM parts were still there or somebody changed them with Delco parts.
Robbabob
Member
- Dec 10, 2012
- 1,096
Might as well change ALL the fluids, oil, trans, power steering, Dexcool (ONLY) coolant, etc.
REMEMBER TO REMOVE THE FILL PLUG BEFORE YOU DRAIN THE DIFFERENTIALS AND THE TRANSFER CASE. Draining the fluid before you realize the fill plug is frozen is not fun or cool.
When you cleaned the TB, did you remove the IAC and clean in there real good?
I know I am not helping much with your main challenge, I'm still hoping someone else with more knowledge will chime in.
REMEMBER TO REMOVE THE FILL PLUG BEFORE YOU DRAIN THE DIFFERENTIALS AND THE TRANSFER CASE. Draining the fluid before you realize the fill plug is frozen is not fun or cool.
When you cleaned the TB, did you remove the IAC and clean in there real good?
I know I am not helping much with your main challenge, I'm still hoping someone else with more knowledge will chime in.
your effort is appreciated. i do change the oil regularly. i drained and filled the coolant around 185k also. i'll have a look at the other fluids you mentioned. i don't think i'm sure what an IAC is. i did remove the throttle body when i cleaned it; both times.
Robbabob
Member
- Dec 10, 2012
- 1,096
Idler Air Controller
It would be attached to the TB, removable. When I cleaned our TB for the first time, I didn't realize the requirement to remove and clean inside that attachment. It is necessary and it may solve your issue; since it is at idle speed your issue occurs within. I really hope this can resolve your issue!
While I am very surprised nobody else has chimed in, some new rules may be preventing them from doing so. New rules require actual technical input to a tech question. I've not received any warnings, I assume, because I have tried to help with little actual expertise. Others may be afraid to add any content due to any little input they may give, which then might result in a warning to them.
It would be attached to the TB, removable. When I cleaned our TB for the first time, I didn't realize the requirement to remove and clean inside that attachment. It is necessary and it may solve your issue; since it is at idle speed your issue occurs within. I really hope this can resolve your issue!
While I am very surprised nobody else has chimed in, some new rules may be preventing them from doing so. New rules require actual technical input to a tech question. I've not received any warnings, I assume, because I have tried to help with little actual expertise. Others may be afraid to add any content due to any little input they may give, which then might result in a warning to them.
i'm new here and didn't know anything about any rules like that. my post says "108 views". so, i don't know, but when the rain clears here in a day or so, i'm going to have another look for this AIC. thanks again! i will post my findings in a few days
FYI,jeff180 said:
All "Drive By Wire" systems that I have seen, (including GM 305/360/370 with the 4.2, 5.3 and 6.0) have electronic throttle bodies so they don't have a separate IAC (Idle Air Control).
An IAC is found on most cable operated throttle systems so the computer has direct control of the idle speed. Some early cable operated systems used an Idle Speed Control (ISC) that was motorized and moves the throttle plate for idle speed control.
no worries Robbabobb. i'm willing to listen to any ideas at this point. the issue is just really strange in my experience. BRoman Jr ,i didn't think i remembered any thing around the throttle body when i took it off to clean it, but i was sure going to look again lol i have very limited knowledge/experience as a mechanic, but i'm fairly decent with my hands and follow instructions well, i think 
Mounce
Member
sorry about the late reply. the SES light IS on, but it has been traced the the air check valve. yes, i reset the PCM. Could voltage be an issue?
I to have a 2005 trailblazer that has a surge at idle. I notice it most when hunting and idling down an old road, the rpms will raise and lower. Just wondering if you got the issue solved?
I've cleaned the throttle body and done pcm relearn, no SES light.
I've cleaned the throttle body and done pcm relearn, no SES light.
Don't know if this'll help, but vehicle surge when releasing the accelerator used to also be a vacuum issue. Check your throttle body and intake gaskets as well as the brake booster hose and purge valve line.
no resolution yet. i plan on checking the things Bluto4x recommended. after paying closer attention, it doesn't seem to be so much a "surge" rather than the engine recovering from a dip. idle drops, then shoots back up.
i'm hoping to get out there this week and will report back this weekend or early next week. thanks to everybody for the great ideas!!