Idle problem, I have searched and still need help...

[Strike One]

I have looked at tons of websites and looked through posts on this board but nothing will help. I think my problem is a little different than most. Please see below, I outlined the idle in steps, hope it is easier to follow that way.

1. Car starts fine, idles fine at about 700-725. Runs fine as well.
2. Once car has been driven for about 5 minutes and is warmed up, idle will start to hang when I press the clutch in and come to a stop. Hangs at about 1200 and then falls to about 900 after a few seconds and sticks there. The car also runs a little rougher.
3. If I let the car idle at a stop for exactly 54 seconds, the idle will suddenly drop back down to 700-725 and my hanging idle surge goes away until the car is shut off. The car once again runs good once the idle has dropped to normal.

I hope this makes sense how I described it. I am guessing since the car adjusts the idle after 54 seconds each time the computer is recognizing a problem and adjusting it. I don't have any codes and have tried all the methods like adjusting TPS, cleaning IAB, buying new IAB, cleaning throttle body, etc.

Any ideas? Could the O2 sensors maybe have anything to do with this? Thanks for any help.

 

[wrathchild]

I dont think its your 02 sensors. I had a hanging idle rolling to a stop then at a stop it would drop. I replaced the 02 sensors and it still does it. Good luck

 

[HISSIN50]

the VSS keeps the idle hanging while coming down to idle while still rolling (get off the highway, stick it in neutral and coast - the idle should not drop to 700 RPM very fast, but hang at ~1500).
it keeps the engine from dropping revs too fast and dying - a nice feature if you have ever had a car that liked to die under said circumstances.

that is my guess. good luck.

 

[lubeboy]

also check your egr valve and the sensor..make sure its not sticking and it moves freely...good luck

 

[HISSIN50]

also check your egr valve and the sensor..make sure its not sticking and it moves freely...good luck

the EGR sticking would kill the idle - not make it higher.

 

[Strike One]

I dont think its your 02 sensors. I had a hanging idle rolling to a stop then at a stop it would drop. I replaced the 02 sensors and it still does it. Good luck

Is your problem similar to mine where the idle will go back to normal after the car is sitting for a specific amount of time? (like how mine goes to normal after 54 seconds)

 

[Strike One]

the VSS keeps the idle hanging while coming down to idle while still rolling (get off the highway, stick it in neutral and coast - the idle should not drop to 700 RPM very fast, but hang at ~1500).
it keeps the engine from dropping revs too fast and dying - a nice feature if you have ever had a car that liked to die under said circumstances.

that is my guess. good luck.

Then should I check for a bad VSS? Would that possible cause my problem?

 

[ironmedic]

i had that exact same problem with my stang. it would be good to go and i drive away. minutes later when i come to a stop, it hangs at like 1200 rpms and wont come down. i had to shut the car off and turn it back on and it goes back to normal. i changed my inlet air controller valve and it fixed everything fine. also check your gaskets around your TB to make sure its not broken as well.

 

[Strike One]

i had that exact same problem with my stang. it would be good to go and i drive away. minutes later when i come to a stop, it hangs at like 1200 rpms and wont come down. i had to shut the car off and turn it back on and it goes back to normal. i changed my inlet air controller valve and it fixed everything fine. also check your gaskets around your TB to make sure its not broken as well.

Thanks for the help but I think our problems are a little different. When my idle drops back to normal after the 54 seconds, if I shut the car off, I will have to go through the whole cycle again when I start it next time. I changed my IAC (same as the IAB, right?) but still nothing.

 

[blk92stangg]

how long have you had the problem? Since the problem seems to happen once you warm up, maybe check the engine and intake temp sensors?

 

[Strike One]

how long have you had the problem? Since the problem seems to happen once you warm up, maybe check the engine and intake temp sensors?

I have had the problem for about 7 months and no matter what I try I can't pinpoint it. I mean it doesn't affect performance, it is more of an annoyance because when I start my car I want to just be able to go without having to work on my idle. I will check the temp sensors out, I haven't looked at them yet. Thanks

 

[kovacs]

Hanging rolling idle

I dont think its your 02 sensors. I had a hanging idle rolling to a stop then at a stop it would drop. I replaced the 02 sensors and it still does it. Good luck

I had the exact same problem for almost 2 years. Its the idle air control valve, its a small electric motor on the intake just above the throttle body. I tried to clean the carbon out of it at first which fixed the problem for a few days then it got a lot worse. At which point i replaced the pricey little part and all was good as new.