Rough idle with several engine codes popping up

holytornado84

Original poster
Member
Feb 21, 2013
111
I have recently been working on getting my 2004 trailblazer LS 4x4 back on the road and running well. I have changed out the front differential and the front axle disconnect here recently but now I have an idling issue. The truck idles like it's missing on a cylinder or not supplying the right combustion mixture ratio.

In the past I believe the P0410 code has came up on it. I don't think I ended up doing anything about it because it was running fine back then. Today I got it scanned at the auto parts store and now there are three codes. P0410, P0495 and I can't exactly remember what the other code was but it was a code about operating temperature for the thermostat and I went ahead and purchased another thermostat.

I am going to run a can of seafoam through the injectors and fuel supply along with running some Seafoam top engine cleaner through the intake or the brake booster. I am also pretty sure that I need to change my O2 sensors being that I have never touch them and have drove my car well over 100,000 miles since I bought it back in 2010. It has 212,000 miles on it now.

If anyone has any information on what is going on with the idle, it would be greatly appreciated. I figured there may have beenquite a few instances on here where members have dealt with these codes before.
 

Sparky

Member
Dec 4, 2011
12,927
P0410 is just the stupid SAIS - kill it with fire. Thing is, check it to make sure it isn't leaking air where it shouldn't. Coworker bought a 2007 LS that has SAIS and the one tube was completely missing, causing it to act up. Dealer replaced the tube at no charge since they somehow "missed it."

P0495 is the cooling fan control circuit. Check the wiring to it, I've heard it can get chafed sometimes. That can also affect some other circuit that shares its reference voltage, I forget what.

Does it not idle right when cold, warmed up, or both? If you give it gas, does it smooth out?

Might be worth just pulling the coils and plugs, make sure they are good and clean, and put it back together. Maybe it got some water down a plug well and it is partially grounding out a cylinder.
 

holytornado84

Original poster
Member
Feb 21, 2013
111
The idling issue seems like it clears up when accelerating and at normal driving speed's. Just on idol is where I notice it. I have just replaced the plugs with AC Delco iridium plugs a few weeks back however, I did notice that a lot of the coil packs had corrosion on the outer portion of the wall that sticks down into the top of the engine.

I also do notice a noise that sounds like the fan is on pretty much constantly. I can't tell if it is running constantly at driving speed's due to not being able to hear it, but I can notice it every time I take off from a dead stop. When the guy read the code from the reader, it said fan speed too high
 

Sparky

Member
Dec 4, 2011
12,927
It may not be missing, entirely possible the mount(s) are shot causing it to just shake badly.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
It's the pedal sensor/throttle circuit that can be affected but that's when the fan clutch is messed up internally and buggering up the 5V reference. That isn't happening here.

Try unplugging the fan clutch and see if the fan noise goes down after initial start up. If not, it might be partially or completely locked. You will get other codes for the unplugged fan clutch. Just keep an eye on the temps and don't use the A/C. Also a good time to check the wiring.

Rough idle is usually associated with a recently cleaned throttle body but not disconnecting the battery to reset the PCM. But at that mileage, wouldn't surprise me if it's the engine mounts, which can make the engine seem shaky.
 

holytornado84

Original poster
Member
Feb 21, 2013
111
Well the car started overheating a little and I still hadn't changed the thermostat out yet. It would only over heat when sitting still and especially when the AC was turned on. It was getting as high as I'm guessing 225 (back and forth from 2 to 3 notches over 210) when sitting still. Then when back up to speed it would gradually cool back down to just under the 210 mark. This was in an evironment of 95 degrees outside.

I brought it home and went ahead and changed the thermostat. Took it back out and it eventually started doing the same thing almost but would only get to the 2nd notch over 210 now. However later when the sun went down and it was about 20 degrees cooler, the car seemed to maintain itself at or just below 210 regularly. It visually looks as though the fan is not moving fast enough when in park sitting still.

@Mooseman, I believe you're onto something. I just cleaned the throttlebody whenever I've changed the spark plugs and did all the work to the front differential and the disconnect. I'm pretty sure though that I had the negative cable disconnected during this process for quite a while and if I didn't, I know I disconnected it yesterday while pulling the alternator to get to the thermostat. However, the somewhat rough idle remains.

On another note, I drove my car about 300 miles yesterday after changing the thermostat and now I am experiencing a hesitation or miss at about 40 or 50 mph with the throttle depressed about 1/8-1/4 of the way down. It feels as though during that period of acceleration with the throttle pressed in only that far, there is missed combustion episodes from a certain cylinder but whenever I press it further down, it straightens out and runs correct. I don't really know how to explain it except for I am going that speed and then I try to accelerate a little more and I can feel the power kick in but there are very small periods that the power just drops for a split second ( A 10th of a second maybe, probably why I associated it with dropped combustion sequence) and then comes back and then repeats again until I either let up on the throttle or push down further on it. It's really weird
 
Last edited:

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Have you checked the fan clutch? Check out this thread for info on how to check it for proper operation but you have to fix the P0495.
How to test the electro-viscous fan clutch

But, if it's overheating, P0495 says that the fan is operating at to fast speed, which should actually help. Strange.

One other possibility is that your cat is clogged and causing the overheating. You could get a backpressure test done or try to remove the O2 sensor and see if things improve. Could also explain the hesitation/miss. How's the power and fuel consumption?

Other than that, did you try cleaning out the condenser and radiator? Bugs and dirt can sometimes clog the fins. Maybe the rad is clogged internally.
 

holytornado84

Original poster
Member
Feb 21, 2013
111
Well in the last month I have checked the fan clutch and also pretty sure I've found my culprit for my misfire. I finally had a P0305 pop up on my dash so I was able to narrow it down to a coil pack on that cylinder. My gas has been around 15mpg which is nowhere near the 19-20 mpg highway that I have been used to getting in the car. The fan was working correctly from what I could tell. I started the car with it warmed up all the way to running temperature and stopped the fan manually with a rag and it was indeed tugging and trying to run again.

I am interested in seeing what you guys think about what brand of coil pack that I need to purchase as I have no clue. I also bought a OBDII scanner and was interested in seeing if anyone knew what the readings on each of the O2 sensors were supposed to look like because I think I still probably have the original factory O2 sensors on it with over 200k on the car. I don't think the cat is clogged or anything but is there an easy way I can test it?
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
For coils, I'd stick with ACDelco or Delphi. I had bad luck with a Standard once so it's off my list.

If your cat is clogged, you'll know with lower power and MPG. You could do an exhaust backpressure test to be sure. If you didn't run it too much with the miss, it should be fine.
 

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