Rough Idle

Freddy G.

Original poster
Member
Dec 4, 2011
55
First I want to say I am sorry for posting on this topic again! I cleaned the throttle body, I cleaned my Cam Shaft Position Solenoid, and changed my spark plugs. Rough idle is mainly when I turn on the AC. When I come to a stop it idles down to 250-300rpms and feels like it wants to stall. I also noticed it does this same thing if say my windows are all the way up or down and I hold two window buttons at the same time and it also idles down/rough idle. my RPM's sit at 500. Should it be higher?
 

MacMan

Member
Mar 3, 2012
194
I sure hope you mean 250-300 and 500 RPM's.

The normal idle on these engines is 600 RPM.

Did you disconnect the battery for at least 35-40 minutes while cleaning the throttle body? Did you remove the throttle body from the engine and clean BOTH sides of the throttle plate?
 

Blckshdw

Moderator
Nov 20, 2011
10,657
Tampa Bay Area, FL
Your idle RPMs should be around 600... How's your running voltage looking? Do you have a meter to check it at the battery?
 

Freddy G.

Original poster
Member
Dec 4, 2011
55
I will have to stop by AutoZone tomorrow and have them check it. Yes I cleaned both sides of the throttle body plate, but I am not sure if I disconnected the Battery while doing so. I have done it several times now so can't remember. I did disconnect the battery when I changed my spark plugs.
 

MacMan

Member
Mar 3, 2012
194
Freddy G. said:
I will have to stop by AutoZone tomorrow and have them check it. Yes I cleaned both sides of the throttle body plate, but I am not sure if I disconnected the Battery while doing so. I have done it several times now so can't remember. I did disconnect the battery when I changed my spark plugs.
Since throttle body spray cleaner is relatively cheap, I recommend doing the cleaning again, and MAKE SURE you disconnect the battery this time....35-40 minutes minimum.
 

Blckshdw

Moderator
Nov 20, 2011
10,657
Tampa Bay Area, FL
Follow up question, how long ago did you clean the throttle body? If you've driven for any appreciable amount of time since then, the PCM has already relearned the clean conditions. No need to reclean, or disconnect your battery just for that. You'd be increasing the chance one of your HVAC actuators takes a dump on you. :duh:

The fact that you can replicate the problem by holding your window switches when the regulators are at their limit, tells me there's something electrical going on. A load test on your battery and alternator might be a good idea.
 

seanpooh

Member
Jan 24, 2012
461
You seem to have the symptoms of bad motor mounts. (Just a suggestion)

If you're in D or R, are at a full stop and the idle is rough I believe it's too much vibration going on messing with the 600 RPM idle. Especially if you have the AC on it will add more stress.

Throttle body and spark plugs don't seem to be an issue.

Do the battery disconnect and see how it goes from there.

If a rough idle is still persistent, then you can have someone behind the wheel that you trust; tell them to put it in D and press hard on the brakes while s/he rev on it. You equipped with a flash light, check out how the mounts are reacting.
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
seanpooh said:
You seem to have the symptoms of bad motor mounts. (Just a suggestion)

If you're in D or R, are at a full stop and the idle is rough I believe it's too much vibration going on messing with the 600 RPM idle. Especially if you have the AC on it will add more stress.

Throttle body and spark plugs don't seem to be an issue.

Do the battery disconnect and see how it goes from there.

If a rough idle is still persistent, then you can have someone behind the wheel that you trust; tell them to put it in D and press hard on the brakes while s/he rev on it. You equipped with a flash light, check out how the mounts are reacting.

That doesn't explain why it only happens when the AC is ON or there is a heavy electrical load.

As Blckshdw said, get the battery and alt load tested.

Also, how old is the battery?
 

Freddy G.

Original poster
Member
Dec 4, 2011
55
Motor Mounts: When I had it at Chevy they told me I had a bad motor mount(the motor mount had a leak, he says they are hydrulic fluid filled? never heard of such a thing myself) But My engine doesnt jump so I didn't think that was true.

Battery: Battery is less then a Year old

I am going to stop by Autozone today and have them load test it
 

Blckshdw

Moderator
Nov 20, 2011
10,657
Tampa Bay Area, FL
Freddy G. said:
Motor Mounts: When I had it at Chevy they told me I had a bad motor mount(the motor mount had a leak, he says they are hydrulic fluid filled? never heard of such a thing myself) But My engine doesnt jump so I didn't think that was true.

That's cuz you're not on here often enough :poke: A bad motor mount won't cause your engine to 'jump', but the truck will idle rough when the transmission is in gear (drive or reverse) and smooth out in park or neutral.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
seanpooh said:
You seem to have the symptoms of bad motor mounts.
I wouldn't say so. Motor mounts generate a vibration at exactly idle frequency (600 RPM = 10 Hz). It's a rotational vibration you can see on the intake manifold side of the engine the best - and the plastic piece vibrates between 1/4 and 1/2". Worse in DRIVE, when it starts it doesn't happen in PARK or NEUTRAL because it's a mechanical oscillation at the 10 Hz resonant frequency of the mass of the engine and transmission together with the driveshaft and the looseness (lash) of the rear diff and gears and axle shafts. Often gets better when warmed up because it changes the stiffness of the mounts.

A motor mount vibration is annoying, but never changes the idle RPM on the tach or a scan tool and it can't ever stall the engine or change with the AC on or off.
 

Freddy G.

Original poster
Member
Dec 4, 2011
55
Just got back from AutoZone. Did a load test and my volts are at 14. Turing Ac on and off and no change in Volts.
Also scanned for any possible Codes and Nothing.
So now that they are ruled out what else can I do? Have my idle raised to 600(at 500) now.
I only cleaned my Cam Shaft Solenoid, never put a new one in. (appeared to look in in pretty good shape and wasnt really dirty)
Brand new plugs already installed.
 

agentdenim

Member
Sep 13, 2013
1
I'm in the exact same boat with a 2004 GMC Envoy... any thoughts on this? Sorry if I'm reviving an ancient thread inappropriately... and I will keep searching.
I didn't do anything with a cam shaft solenoid recently, but it was replaced late last year. Same with plugs, and just did a whole throttle body cleaning when I did the plugs, and I'm certain battery was out.

Freddy, question for you. Is your vehicle eating batteries faster than usual? Someone else here mentioned an electrical issue... I've been thru 3 batteries in the past 6 years which seems a bit much to me. I'm going to have to look into that too... maybe a short?

- Aric


Freddy G. said:
Just got back from AutoZone. Did a load test and my volts are at 14. Turing Ac on and off and no change in Volts.
Also scanned for any possible Codes and Nothing.
So now that they are ruled out what else can I do? Have my idle raised to 600(at 500) now.
I only cleaned my Cam Shaft Solenoid, never put a new one in. (appeared to look in in pretty good shape and wasnt really dirty)
Brand new plugs already installed.
 

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