More idle hang info

[Todd Richmond]

I finally got tired of trying to drive in traffic with a 1700rpm idle and decided to get serious about fixing it. After reading all the threads, I found out the problem was something that no one has mentioned - weak throttle return springs!

Things I tried first:

1) reset PCM - no noticeable help
2) make driver's side throttle body open first by a hair - made the problem slightly worse
3) add 3/4" dowel with 21/64" hole as recommended by Sean Roe - significant improvement but still random hangs. A smaller hole caused a rough, surging idle, especially when cold

While playing around on test drives I accidentally noticed that if I kicked the gas pedal, the hang would stop on the times when it didn't do so 5 seconds after a complete stop. At first I thought the throttle cable was sticking slightly, but it turns out the driver side return spring was too weak. This is hard to diagnose because the passenger side was strong and so together, just pulling on the throttle cable makes you think both sides are returning properly. The key with Vipers is that there is usually a very slight amount of play on the driver side before it hits the stop screw to start rotating the passenger side - this is exaggerated by people who add a little extra play as mentioned above and accounts for my negative effect

To diagnose this problem, hold the passenger side shaft open a few millimeters(to negate its spring) and make sure the driver side returns FIRMLY against its stop. I had to use needle-nose pliers to bend up the spring on the rear 1/2 of the shaft (not in the front where it stops on the shaft itself). It is probably worth verifying that the passenger side spring also returns strongly

$2.39 for a dowel and a couple hours tedious labor - Problem Solved!

 

[ChicagoGTS]

So did you leave the dowel rod in, or did the spring adjustment work by itself?

 

[MaxedGTS]

what throttle bodys do you have. the stock or accufabs?

 

[thebigsnake]

If this works it'll be great, as its a mechanical fix(which I can figure out).
I have that problem intermitantly. This morning she was idling fine(700rpm), but last time at around 1,700rpm in traffic.

 

[Torquemonster]

Todd - this is good useful information. Amazing how sometimes it is the little simple things that fix problems - thanks for sharing

 

[01sapphireGTS]

I will check my springs ASAP. Thanks !

 

[Todd Richmond]

I left the dowel in - it does seem to kick down a bit faster with it, though by the time I fixed the spring, things were working so well that I didn't go back and seriously verify.

I have stock throttle bodies that the previous had honed smoothe

The bad spring basically was strong enough to close the throttle from 1/2 or greater opening, but not from a slow return that occurs often when driving in traffic. The result was that the driver side was open a VERY VERY slight crack, but enough to increase the idle nearly 1000RPM (or maybe enough to interfer with the PCM control). When you check, let the throttle close very slowly and then try to push it closed further. If you note any further shift in the throttle(possibly just a small vibration or clunk), you might have the same issue - quite a minute difference was enough to drive my GTS (and me) crazy. If both springs return w/ the same force and stop solidly, there is some other problem

 

[ChicagoGTS]

Todd, This is exactly what I am seeing on my accufab's tried it yesterday and to the last detail I experienced it all, nice work. How did you fix the spring, could you possibly post pics?

 

[Todd Richmond]

Glad this helped - it had driven me nuts for over two years and was so hard to detect because people usually test by blipping the throttle which allows enough inertia to close everything up properly

I ended up just using needle-nose pliers to pull 1/2 of the dual spring up to catch on a notch a few mm up from its normal location. I also wound both springs a little by pulling up on them, but there really isn't enough room to add much tension that way. The best solution is probably to take everything apart, but that is a project for another day. My idle also seems a tad rougher than before so I might play around with a slightly larger hole in the dowel

 

[STUGOTS]

Guys i had the idle hang as the rest of you, I got 70 mm TB's (accufab) and no more idle hang, no idea why.

Also the vec 2 solves this problem.

 

[ViperGTS]

>>>Also the vec 2 solves this problem. <<<

My guess from the beginning: this is a software related problem...

 

[PRVT JET]

VEC1 will also fix this problem, it did on my car.

 

[Jack B]

For those that are not familiar with the VEC2, the program allows you to zero out the long term fuel trim. This in turn reduces the short term adaptives at idle. The VEC1 does not have this capabality. If the VEC1 helped it was only luck.

What would be interesting would be to put a scan tool on when the idle hang is occurring and look at the short term fuel trim and idle or in fact if the long term is changing. Once again if it is a mechanical issue only ingenuity will fix the problem.

 

[STUGOTS]

My accufab 70mm TB's fixed mine.

I have the vec 2 but have not had it installed yet.