Idle when comming to a stop

[trhenry1]

When coming to a stop in my 99 Tahoe, periodically it want to remain at 1K rpm until vehicle comes to a complete stop then drops back to 600 rpm. The higher RPMs are naturally wanting to push me while breaking, so extra breaking force is required to come to a complete stop.
:help:
I took out the idle control valve on the throttle body and cleaned it, but didn't seem to help. I had to clean it once before and there was so much carbon build up on it I was sure it would look the same this time, but it was fairly clean when removed. Last time I cleaned it did help. Is there a test I can perform on the valve that will tell me if it is starting to fail. Seems worse after taking longer trips. :smiley-face-popcorn

 

[lesterl]

Does turning the AC on cause the idle to change?

 

[bertman]

I am just started experiencing the same issue today. I notice when I put it in gear that the RPM's rose and I had to hold the brake to keep it from running away. I am not sure where to begin to look. It doesn't matter if I am in drive or reverse, it idles higher for a while but eventually goes back to normal. It would be nice if someone could throw a bone here. Definitely not the A/C cause mine is not working currently.

 

[lesterl]

Check throttle cable for binding, check throttle plates for sticking slightly open (carbon buildup in the throttle body), Check Idle Air Control Valve, Check for vacume leaks, check TBI base gasket if TBI (since no year posted bertman) OP skip that step....

 

[bertman]

Thanks lester! I forgot to mention that my Tahoe is a 1999. I will give all of that a run thru and see what I can find. The funny thing is when in park, the idle is fine, and just as soon as I put it in gear (any gear) the idle goes high. I would think that eliminates mechanical sticking problem. Maybe not!!!Vacuum is an engine killer I know. I will start there.

 

[Mayhem]

My guess, sounds just like what I went through. Intake gasket leak. Just replaced mine for a misfire issue and problem solved. Dealer wanted $900 to replace $25 worth of gaskets. (can we say ouch) I did it in 8 hours. Well worth it in my option. But, what I did was take it to dealer and had them diagnose the problem for $90 instead of hit and miss by buying parts I don't need.

 

[lesterl]

Dealers dont always guess right when diagnosing, unless you have a good tech... If someone wants to try to do their own repair with my diagnosis, I am happy to let them try to repair it, but I dont feel sorry if I was wrong or if they screw something else up. If I am paid to do a repair and my diagnosis is wrong the rediagnosis doesnt cost anything extra and usually I will work with people on the parts and such.... No such guarantees on the try it yourself way.... altho on these rigs a LIM gasket job is a pretty good one to do needed or not....