Rough Idle...

n847

Original poster
Member
Apr 23, 2012
6
Long time no see...Thats a good thing means my TB has been running good.

First off the truck is an 03 I6 EXT with apx 138,000mi..
I've been working out of town over the last week and I'm leaving again tomorrow. My wife called me on Tuesday complaining of a rough idle. It started after adding gas when the fuel was low enough to turn on the fuel level light. She then added more gas after an hour or so at another gas station to see if she had forgotten to close the cap all the way or got bad gas. I had her add some water remover and fuel injector cleaner to the tank as well. She was getting a code.

Her description of the problem is a rough idle accompanied by a vibration that gets a little better as speed increases. I'll be taking the truck out for a drive as soon as I move a few things around the garage to make room to pull it inside.
She took the car over to my dad he ran his OBDII scanner and the only had the code for low engine temp (we get it once or twice a year clear it and it goes away). He cleared the code no change. I was reading over the last few days and got to thinking about the crank position sensor. So I ordered one from Rockauto along with air and oil filters since the light just came on last week. I also ordered a fuel filter even though I replaced one last year.

I got in late last night and started it for a second and noticed it to be a very rough idle, but the tach isn't bouncing around and the SEL is back on now. I also noticed a very strong fuel smell from the exhaust (a very rich smell). That smell has me wondering if there is something wrong with the fuel system and or maybe the O2 sensors. I've never replaced any of the coils (replaced all the plugs and fuel filter last spring and cleaned the TB). I've never messed with the fuel system or exhaust.

I'm going to look into it today although my parts haven't arived from rockauto yet. But if I don't get it figured out or fixed I may have to drop it off at my mechanic due to my time constraints. Any suggestions are apprecited!

Thanks in advance guys!
 

n847

Original poster
Member
Apr 23, 2012
6
After driving the truck my self I noticed it does have a very rough idle that does not go away at any speed. I'm noticing a vibration that doesn't go away in any gear including park or neutral. It also has a service engine code, that I will have to get my dads scanner to check again. When I'm drving the light will occasionally blink, but at idle or when the engine isn't under strain the light is solid. I also can't get the light to blink in park or neutral. The engine doesn't feel like its running on all 6 cylinders. I have noticed the tach does bounce around a little it idles around 600 and it wiggles just enough to be noticable. The miss/vibration and a little noise is most noticable when you fist start to pull away from a stop. I'm starting to think this is something I'll have to drop off at my mechanic because I don't want to leave my wife with out a vehicle for another 2 weeks and I'm leaving again tomorrow.

I've never seen the blinking SEL before so I'm going to do some more searching on here!
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
n847 said:
I've never seen the blinking SEL before so I'm going to do some more searching on here!
Searching in your Owner's Manual would have been a faster way to get you to STOP DRIVING it, which is my advice. Your symptoms are classic misfire, and a blinking SES means a misfire bad enough to be dumping unburned fuel through the cylinder(s) so that it ignites and burns in the catalytic converter and you're about to catch fire or destroy your cat and that's real $$$.

You have a bad plug or coil, most likely, or you didn't use Delco 41-103 plugs. In any event, get the code read, and it will probably be a P030X where "X" is the cylinder number of concern, or a "0" which is general misfire that the PCM can't figure out a single cylinder at fault for. It could also be bad fuel getting through a bad filter and clogging the injectors, but that's less likely. Pull the plugs of the cylinders of interest and check them and find out if they look different from a normal plug. Replace as necessary.
 

n847

Original poster
Member
Apr 23, 2012
6
Thanks Roadie! Thats what I've decided to do based on what I read. I didn't know about the blinking light till I drove it my self, thats why I brought it straight home. I'm sure thats why the strong fuel smell. I'm hoping I haven't trashed that cat!
 

johnnytutos

Member
Dec 2, 2012
4
I cant wait to hear the results. Im going to change all my plugges as well. I have the same exact symptoms with out the flashing SEL light just always got a "low engine temp" reading
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
johnnytutos said:
... always got a "low engine temp" reading
Time to change the thermostat before the rich mixture sends enough fuel through to kill your *expensive* cat. Owners defer fixing the P0128 code far too often, not understanding they're not saving any money due to lower mileage and the risk of killing the cat.
 

johnnytutos

Member
Dec 2, 2012
4
Got the Plugs, Thermostat and ready for tomorrow morning. should i put any product on the piston tops thru the plug holes while changing the thermostat to eats away any build up?
 

CaptainXL

Member
Dec 4, 2011
2,445
johnnytutos said:
Got the Plugs, Thermostat and ready for tomorrow morning. should i put any product on the piston tops thru the plug holes while changing the thermostat to eats away any build up?

GM Top Engine Cleaner or equivalent can be added to the top of pistons to let soak. Follow directions per applicable TSB.
 

n847

Original poster
Member
Apr 23, 2012
6
Thanks guys I took the truck to my mechanic he used his scanner and found the number one cylinder to be the issue. So he put a new coil on it for me and had it done by the next day. Only charged me 25 bucks labor because he knew I wouldn't have had him fix it if I hadn't been out of town. Oh and I did ask him to confirm that I did use AC Delco plugs.

the roadie said:
Time to change the thermostat before the rich mixture sends enough fuel through to kill your *expensive* cat. Owners defer fixing the P0128 code far too often, not understanding they're not saving any money due to lower mileage and the risk of killing the cat.

Roadie I will do a little research on here, but I was told when I got the low engine temp light which happens about once a year it wasn't a big deal and I assumed this was true since I would just clear the code and the light would stay off for months at a time. Needless to say I will replace the T-stat, do I need to replace the temp sensor? Can someone please explain the real issue with this "engine temp too low" code?

I was also wonding how to check if I need to replace the 02 sensor or should I just do it. The truck has over 130k on it and I've never changed it in the 50K I put on it.

Thanks again guys!
 

johnnytutos

Member
Dec 2, 2012
4
changed the thermostat, oil, and plugs. runs much smoother but still that noticible vibration like the blancer if off somewhere. The plugs i pulled out were horrible and much shorter.
now i just have to find and test the darn Encoder curicut, thats what my Solus says, i can engaged the front dissconnect, lock and unlock the encoder locking mech, probably fried a wire, tried a new TCCM but it didnt even register
 

Forum Statistics

Threads
23,229
Posts
637,063
Members
18,390
Latest member
jgriff

Members Online