High Idle/Bad Coasting

[mackdaddy77]

I have a 1997 Grand Am GT 3.1L V6 with 85k miles on it. Recently it has begun having problems idling and coasting down. While in park or neutral, it will idle at approximately 1,500 rpm while the normal idle and in-gear idle is nearer to 750 rpm. Another problem that I have found is that the car will not coast down normally. If I let off the gas at around 50 mph, the engine will continue to run at approximately 1,500 rpm and sometimes even accelerate a bit without any help from the pedal. Some have told me to check the vacuum hoses but I am not sure what to be looking for or how to test if they are bad. Many thanks and appreciation for any help you can give me.

[xeroinfinity]

Yes I would say check the vacum lines that are on the intake and the air intake. You would hear a hiss or whistle noise around the area that had a leak.

Could also be the idle air control(IAC). It is located in the throtle body.
Thier is a test procedure here in the Grand am Tips & Maintenance sub forum for checking the IAC and cleaning the port it sets in.
Sometimes a good cleaning helps idle issues.

It says for a 99 3.4 but it is the same on your 3.1.
Idle Air Control(IAC) Testing Replacing for 99+

Hope that helps and welcome to AF.

[xeroinfinity]

Well I find it odd that you know about the bi-directional scan tool to cycle the ABS modulator, but not where to look for a vacum leak....

[mackdaddy77]

I'm working as an intern for Honeywell this summer, specifically for Bendix. Most of what I've been doing is testing brake pads and shoes on dynos, but I have had a few crash courses on hydraulic systems and theory. I spotted that question the day after a training session with Jay Buckley the Bendix Answerman. I've taken to trying to fix my car on my own this summer as I keep running into seemingly minor things happening all the time. So far I've had a busted heater core, clogged radiator, and obstructed fuel filter; learning more and more, slowly but surely. Thanks for your help!

[xeroinfinity]

I see.
Working with those systems you would use that BDST,
and Jay Buckley is the man and he knows his stuff!

Yea all those little things add up though over time.
And IMO is typical of the N-body, nickle and dime you to death

no prob on the help!