Idling Problems with 2000 Yukon

This is my first time posting on a forum, so please bear with me. I have been having idling problems with my Yukon for a while, but its been getting worse recently. Every time I am at a stoplight or a stop sign, it dips down to about 300, then jumps back up all of a sudden. Today, when I stopped, it dipped down so low, that my car died. Its done this twice already. I am assuming it is a fuel problem, but it could also possibly an ignition problem too. Any suggestions to what it could be, and possible solutions?

Thanks,

Sean

Maybe a fuel filter that is clogged or maybe it needs a tune up. How many miles??

I have already changed the fuel filter, and it didn't help. I think it might be a vacuum line leak or something along those lines. There is 106,000 on the car.

Check your throttle plate just north of the intake hose (butterfly), This throttle body meters air only, due to fuel is delivered by the injectors. In most irratic idle cases it's just a matter of cleaning this plate. The cure is simple, go to your corner auto discount store & purchase a can of intake cleaner (make sure it's sensor safe!) Pull off the intake hose @ throttle body, open throttle plate and apply cleaner to plate and throat. With your finger stretching in as far as you can wipe clean with a shop rag. Repeat process until rag comes out clean. Be careful, don't use more than you need. Reinstall intake hose. (check for cracks in intake hose and replace as needed) Also be aware your first start up may be a "hard start", but once it's running she'll smooth out. Let me know how it goes. This info was given assuming you don't have a active check engine light. Also note : the color of your spark plugs is a sure indicator of a fuel system problem. White or light grey = lean.

any luck??

I haven't done it yet, but it seems logical.. I'll try it tomorrow morning and post the results. Do you have a Yukon?

05 suburban, 03 s-10, 99 silverado & 86 scottsdale (hotrod)

p.s don't forget to clean back side of throttle plate(butterfly)

Idling problem

Thanks man, it worked. I cleaned it out about a week ago, and it hasn't been doing it since. It wasn't that dirty though, I dont know how it could make that big of a difference.

Glad to Help

Glad to help, there are small "air signal" holes just past the butterfly in the throat, also small holes in butterfly itself. Doesn't take much to clog them up and cause an irratic signal. Junk will also build up around the edge of the butterfly, causing it to not seal or close properly. This cleaning process is a good preventative maintenance task that should be done to any fuel injected engine every 50,000 miles or so. Todd

hey im posting for my brother he has a 01 tahoe 5.3L and when the outside temp drops below 50 degrees the engine drops idle to about 300 rpm and then goes back and and then drops almost to a stall and backfires maybe once or more the truck has 102K on it and he just cleaned the throttle plate and everything and this only happens in the morning when it is started first for the day any ideas?

To trouble-shoot a cold start issue, you really need a "live data" obd 2 scanner. It will enable you to see what the engine ecm sees: coolant temp, intake temp, fuel trim, amount of oxygen / fuel in exhaust, & engine timing. All of these things are vital to keeping a cold engine running .The ecm can get a false reading from a sensor without getting a check engine light.

You might also want to try Seafoam. Suck it up through a vacuum hose and watch the crap blow out the tail pipe. That coupled with a TB cleaning should smooth the idle a bit. Also, the MAF (Mass airflow sensor can cause rough idle and stalling issues)

he bought MAF sensor cleaner today and cleaned the MAF and sprayed out the TB because it is sensor safe and this will be the second TB cleaning so we'll see i just hope it isnt an injector.

Gapp said:

You might also want to try Seafoam. Suck it up through a vacuum hose and watch the crap blow out the tail pipe. That coupled with a TB cleaning should smooth the idle a bit. Also, the MAF (Mass airflow sensor can cause rough idle and stalling issues)

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would an aftermarket granatelli maf cause the same issues? The sensor is clean, and i only have the issue when the engine is cold and hasn't been run for a while. It didn't do this when i first installed it but that was earlier in the year when it was warm. Since its been cold the hoe has rough idle, and the engine shakes at idle until at operating temperature. My first thought was plugs and injectors but what do you guys think?

brdnboy said:

...but what do you guys think?

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Uh, I think you need to try searching, lol.....

Here's my post from last month describing the same problems and the cause was the intake manifold gaskets.

http://www.tahoeforum.com/showthread.php?t=2834

kikbaks said:

Uh, I think you need to try searching, lol.....

Here's my post from last month describing the same problems and the cause was the intake manifold gaskets.

http://www.tahoeforum.com/showthread.php?t=2834

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Yes i saw that. Great information! It sounds very similar to my situation but before i spend $250 i want to make sure that is the issue. Is there any possible way it could be spark plugs or injectors or a dirty throttle body? I have cleaned the throttle body, but i just saw JK's post on making sure an area in top left is clear of any gunk. I did a thorough cleaning of the TB but did not focus on this area specifically. I also heard that a slight vacuum leak could also cause these symptoms. I am not doubting you kikbaks and i am glad i have a potential solution. I have done quite of bit of searching here and other places, i just want to be positive before i spend money on something that wont solve my problem. Thanks everyone!
By the way kikbaks was your yukon throwing any kind of code to indicate what was causing the issue or not? Thanks much.

EDIT: I just noticed in your other post that a leaking intake gasket would be the cause of a vacuum leak so, could there be a leak anywhere else in the vacuum system?
Also could i have a warped intake, or is it more likely the gasket? What would cause warping of the intake? Just Heat?

brdnboy said:

I also heard that a slight vacuum leak could also cause these symptoms.

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That's what I'm guessing it is. Just like mine. After it warms up and the steel expands, it seals and runs fine.

brdnboy said:

By the way kikbaks was your yukon throwing any kind of code to indicate what was causing the issue or not?

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The codes retrieved at cold start up were describing misfires but do not pin point the problem.