As the title states my truck is dieing at idle. 2003 chevy blazer 4.3 with 220k miles. Did cap, rotor, wires, plugs and air filter about 15k miles ago. Ac clutch went out a month ago and put a new compressor on it. Yesterday the starter went out and I replaced it today. After replacing it the truck wouldn't start and the security light was on. I unhooked the battery and it cleared everything and started right up. Now I have a new issue when I come to a red light the rpms drop to 200-300 and it bounces up to 500-600 a couple times then stalls out. If I keep the rpms at 1000 at the light it will stay running but as soon as I let off throttle it idles low and dies. I am stumped and don't know what it could be. I have a new fuel filter so I'm going to throw that in and see if it helps. To me it seems like a fuel problem more than anything.

Also I was getting a misfire on cylinder 3 before this and would have a check engine light for that (P0301) and also a cat or 02 code of (P0420). Up until yesterday the truck would idle at a light just fine although it would be somewhat of a roufh idle around 600 it never died. I find it hard to believe replacing the starter would have any effect on the idle but i don't know. I drove about 30-35 miles home after changing the starter and no codes popped up yet.

Any help is greatly appreciated.

 

Just to eliminate the easy stuff, be sure there are no vacuum leaks and that all the hoses are hooked up. I've heard of the one on the back side of the air intake coming loose. It is a hose that is about an inch or so in diameter that goes to the passenger side valve cover (I think).

 

Thanks for the response. Im going to check starter connections and baatery connections now that its home in the garage. Ill go over the vacuum hoses and make sure everything is ok but it wasnt doing this yesterday before the starter went out. So somehow changing the starter out and unhooking the battery today has caused it to not want to idle at all. It runs perfectly fine though and accelerates like normal. I'm stumped lol but something is wrong.

 

The other thing to check if your truck won't idle is the Idle Air Control Solenoid (IACS). It's on the side of the throttle body, and controls allowing air into the engine at idle to maintain RPM around 600ish. The solenoid can seize over time due to carbon and other crud building up. A careful cleaning may get the original one back moving, or it might need to be replaced. I was successful cleaning the solenoid on one truck with an alternating combination of brakeclean, Seafoam and a brass brush.

Off the top of my head I don't remember the testing procedure to check the function of the IACS, but I believe there are instructions on the forum somewhere.

 

Thank you for the reply! Right now it's unhooked in the garage and I haven't had time to mess with it this week. I re connected the battery and double checked my connections on the starter and now I'm getting a security light and the truck won't turn over. Going to try and do a relearn on the key but I have a buddy with an actual diagnostic tool (not my little handheld) and he's coming by Saturday to take a look. If I can get past the security stuff locking the key out I'm confident I can chase down the idle problem. The truck ran fine up until changing the starter. The Alternator is a year old and the battery is only 3 months old both check out fine so I think it's the IAC as well not keeping the truck alive at a stop. She ran great on the way home after changing the starter other than the idle which makes me think it's something small but still a pain in the *** nonetheless!

 

well I just went to try and mess with the truck and went to hook the battery up but the positive cable bolt kept trying to cross thread or would get almost tight and then not go any further. Comparing the two battery bolts to each other the positive side definetly looks mushroomed and the threads are jacked up. Running to get a new bolt in the morning and will post with an update good or bad lol. I am going to grab a new IAC valve as well to change out so if I get it running I can figure out if this is my issue or not.

 

Update for everyone:

Replaced the battery terminal bolts and the security problem went away but it was still very rough idling once it warmed up. I cleaned the IAC valve with some brake cleaner and it idled much better. Went ahead and replaced tbe valve with a new one and she's been running great ever since!

 

Congrats and thanks for the update!

 

Great to hear. Thanks for closing the loop on fixing the issue.

 

Nice call.

George