99 Silverado 5.3l 80,000 miles

Here is my problem. Will not idle at a steady rpm goes between 300 and 700rpm and when you put it in drive going down street speed just keeps on increasing. When you take your foot off the gas it takes a long time to slow down. Fuel pump, filter all lines recently replaced. I have good fuel pressure and steady fuel pressure. No codes. any ideas? Trying to fix all this so I can sell it. Thanks for any help :uhoh:

Here is my problem. Will not idle at a steady rpm goes between 300 and 700rpm and when you put it in drive going down street speed just keeps on increasing. When you take your foot off the gas it takes a long time to slow down. Fuel pump, filter all lines recently replaced. I have good fuel pressure and steady fuel pressure. No codes. any ideas? Trying to fix all this so I can sell it. Thanks for any help :uhoh:

my 2000 5.3L idles at 500 rpm very steady. when cold at first it may idle at 700rpm for a few min.... when hot 500rpm.. things to do are using throttle body cleaner clean the TB and the IAC. remove the IAC and using the cleaner and a tooth brush clean up any carbon. also the bore it sets in. allow to dry before install use air to blow out if you have this available. check the vacuum lines and esp the PCV ... remove vac line to fuel reg see if you have fuel/smell of fuel if so replace the regulator. fuel pressure should be above 52 psi. eng on or off with the key on..

I should have mentioned I did clean the throttle body..Apparently the IAC went bad I did not have an issue until fuel pump was replaced not sure if that can relate to it but anyways replaced and running great now. Thanks for the quick reply.

I should have mentioned I did clean the throttle body..Apparently the IAC went bad I did not have an issue until fuel pump was replaced not sure if that can relate to it but anyways replaced and running great now. Thanks for the quick reply.

the IAC will get damaged from using the wrong cleaner or forcing the IAC valve to move. never use any cleaner like carb cleaner or ??? as this will eat at the motor/valve/plastic etc... only use TB cleaner. when the idle is erratic the vacuum lines or the IAC are the usual failures.