hanging idle . .what gives

[varanus]

My 97 GTS is having idle issues.
Sometimes it will hang up at 1700 to 2500 rpm for quite a while till I gun it a few times to bring down or it will surge back and forth between 700 andd 1000 rpm back and forth.
I have headers, hi flow cats and corsa exhaust , vec 1, and roller rockers.
A few months back prior to the roller rockers It hung up at 2000 rpm for a minute or so and did this a few times. This never happened again until a few days ago.

Anyone with any ideas what it might be?

 

[varanus]

BTW the SC and 70 mm throttle bodies are not on right now

 

[Joel]

Seems to happen on mine occasionally, especially when really hot, think I remember a post about restricting the pipe to the idle valve, but havn't searched. Its a common experience on lots of vipers.

 

[Mike Adams]

Do you have a mopar computer or is your battery low on power. I had a problem with my idle hanging with the mopar computer. Same problem occured on another car when he killed the battery and when cranking the car to start it the voltage would go low enough for the computer to loose its memory for the IAC position.


If you have just adjusted your VEC one this can happen

 

[Viper Wizard]

Check your intake gaskets!

 

[Andrew2KRT10]

Well, I have a VEC 1 and had some idle problems once. I forget what brought it on, but I had to disconnect the battery at the battery. Reconnect. Start the car, let it run for about 20 seconds. Restart, let it run for about 20 seconds, do that about 3-4 times. By the 5th start the idle was good and has been good every since.

Oh, I remember!!!! I had my VEC 1 control unit under my seat. I have a feeling that when I was in Tenn., and the rains came, I think the control box got wet and screwed up the settings. Just a theory, but the only one I could figure out. I guess once it dried out, it was able to accept re-programming.

Since then I installed the VEC control box under the dash near my right leg. It's out of the way, safe, and easy to control and I didn't have to cut into anything to drill any holes to install. I was able to use an existing dash screw hole to mount.
Can't hurt.

Good luck.

Andrew

 

[VIPER1996]

I would agree with Viper Wizard, check intake gasket. Just put new head gaskets in and half the intake bolts weren't tight when we took off the intake.

 

[Bob D]

I recently had that problem and it was the throttle position sensor. It was causing the AIC to stay open.

 

[RockyTop]

You described my symptoms exactly ! My Viper tech traced it to a voltage signal (or something like that ) coming from my VEC . I trust my tech to have traced tyhe source corretly, but given the number of people who have experienced this symptom it must have a myriad of other possible causes. Since then I have reset the ECU and even had it reflashed. The symptom definitely occurs much less often, but pops up ocassionally. I still have my VEC on the car.

Low battery, TPS, idle [air ?] motor, etc. can all cause this symptom.

Happy hunting !

 

[Mark Young]

Its common. My '99 will hang on rare occasion - and I don't have any add-ons - which seem to exacerbate the problem. It can be caused by different issues though.

Call and talk to Wayne at Apex. He and I were talking a while ago and he told me this problem appears with various cam changes/add-ons they've experimented with on the Lethal packages. He told me they had finally figured it out - so give 'em a call.

 

[JimDavis MT 97GTS 650R]

I agree with what others have suggested...."Check Your Intake Gaskets!" Replaced mine twice in the last 50,000 miles.

 

[varanus]

I disconected the battery today to reset the computer and drove for a while. Seems to have cleared it up 90 percent. Hasn't hung up at 2,000 rpm. Drops down to about a 1000 rpm then takes a sec to drop to 600 rpm.
It does seem slow to drop revs compared to some other cars. Could it be characteristic of a big torquey motor or havy flywheel?
Although the 1000 to 600 rpm slow drop has me wondering if the TPS is starting to go out.

If I had leaking manifold gaskets, wouldn't the idle be consistantly off rather than surging? We did just put the manifold back on last week.

 

[JimDavis MT 97GTS 650R]

I think you will find the battery disconnect only a temporary fix. More than likely the problem will return. My past experience almost always turned out to be a intake gasket leak or low battery voltage. In the unlikely event that you have a battery over 3 years old, replace it. Your car requires good strong voltage to function properly. As for the intake gaskets; even new ones can fail. For what it's worth, my idle was surging with intake leaks. Hope this helps. (JD)

 

[jcaspar1]

Had the rpm stick at 2000 before due to low battery. Has not happened since it was replaced under warranty. The pause around 1500 is normal.