Adjusting Idle

**Taylor** · 11-11-2013

I understand that vipers seem to run low on rpm at idle, mine seems to run around 450-550 on the tach, but it seems to run so low that it's rough, otherwise car runs great, no hesitation at all or rough spots while maintaining rpm in any gear, very smooth, except at idle.

Any suggestions on how to raise the idle?

Thanks

Mike

**slowhatch** · 11-11-2013

Isn't there a small set screw on the throttle body to adjust? Also make sure your IAC valve is gunked up, and you dont have any vacuum leaks causing you to idle low. If you just raise the idle by adjusting the tb, it could bandaid an actual problem--450-550rpm seems awful low.

**Taylor** · 11-11-2013

I will look, just bought the car a couple of weeks ago, love it, just thought idle was very low.

I read on here that the tach is not very accurate and it's probably idling higher but shows lower.

**slitherv10** · 11-11-2013

Originally Posted by Taylor

I will look, just bought the car a couple of weeks ago, love it, just thought idle was very low.

I read on here that the tach is not very accurate and it's probably idling higher but shows lower.

Your probably idling at 600=650 on a scanner but the tach usually shows a tad bit lower. If it is running rough though at 450, then it may be another problem which at this point without being able to diagnose it live, I suggest you have it looked at from a Viper Tech near you.

**DrTaco** · 11-11-2013

As you have seen so far, these cars are all over the place as far as idle goes. 500 on the TACH is normal though, espec if the car is modded. But not normal if it's rough (ie cutting in and out). I know you just got the car, any chance you're not just used to the "Viper shakes"? its DEF a good idea to check and clean your IAC motor and see if anything changes though and have a Viper owner give it a look over.

**Taylor** · 11-11-2013

I just purchased all the manuals for the car, I will do some looking of my own before it goes anywhere, I thought others would run into this and have a quick fix.

**crackleking** · 11-12-2013

I have a 98 rt, and mine, shown on the tach, idles at 400. It idles without any problem, not rough, and the needle stays true at idle all the time. I understand the tach may not be fully accurate, but mine shows 400 without any problems.

ViperGTS · 11-12-2013

RPM below 1000 - the thicker bar is 500! Close to ZERO.
The thin bar is 750.rpm.jpg rpm3.jpg

**slitherv10** · 11-12-2013

Originally Posted by ViperGTS

RPM below 1000 - the thicker bar is 500! Close to ZERO.
The thin bar is 750.rpm.jpg rpm3.jpg

that explains it !!! Always thought I was idling at 450 but looks like I m at 600-650

**uvbnbit** · 11-12-2013

As mentioned, hook up a "real-time" capable OBD and see what it actually is. also, clean the IAC, maybe a pcm re-set might help too.

**Taylor** · 11-12-2013

Please eplain to the viper noob what a IAC is and I will clean it.

**plumcrazy** · 11-12-2013

idle air control

**ICPREY** · 11-12-2013

Sounds like it's just a 708 cam car to me....

If you were having stalling issues or sticking idle then I would start troubleshooting...

**slitherv10** · 11-12-2013

Whats the procedure in cleaning the IAC? ie, removing it and what to use to clean it etc...

**ICPREY** · 11-12-2013

Remove it and clean it with either carb cleaner or mass air flow sensor cleaner.

**Taylor** · 11-12-2013

Thanks for the picture of the tach, I was wrong, it does not idle as low as I thought, must be 650 or so then according to the picture, but it does still idle a little rough,

I will clean the iac and if it's still the same I will chalk it up as the cam as one person said, cars does not stall at all and runs perfect. Could be I'm new to vipers also just coming from a C5 corvette.

Thank you all.

**uvbnbit** · 11-13-2013

wouldnt hurt to do PCM re-set after IAC cleaning too. not sure if there is a how-to on this here yet, but it would be a great post if someone would. hint, hint. You hear that Mr Wizard ?

ViperGTS · 11-13-2013

PCM reset? Disconnect positive battery cable/terminal under the hood for a few minutes.

**Taylor** · 11-13-2013

Reviewed the service manual last night and going to clean the iac later today, I will also disconnect the battery for the PCM reset, thanks guys.

**uvbnbit** · 11-13-2013

You also need to ground the positive cable to frame, battery tray, etc. use a voltmeter to make sure its a good spot. you'll need to do that to "dump" ALL the memory. Turn key on, engine off, push gas pedal to floor to set throttle position. Do this a few times. then, start car and let it idle. if it want's to die, let it-don't try and "save" it. Start again. This is PCM 'learning'. Anything else I forgot Chuck?

DO NOT disconnect pos. cable at jump post! you need to do it at the battery. Inconvenient? Yes.
If you doubt this, send message to the Wizard. my .02

**ViperTony** · 11-13-2013

Originally Posted by uvbnbit

DO NOT disconnect pos. cable at jump post! you need to do it at the battery. Inconvenient? Yes.
If you doubt this, send message to the Wizard. my .02

I've done the post post cable disconnect multiple times to reset the PCM over the years without issue. I think the potential problem in doing so is that if the nut is over-torqued then the post can break which leads a whole new set of unwanted problems. I love and respect Chuck but I think the disconnect at battery advice, while sound, is a bit over-dramatized. But....if disconnecting at the battery then it provides an excellent opportunity to clean the battery tray area while one is in there.

**Bugman Jeff** · 11-13-2013

I used acetone, a tooth brush and q-tips, followed by some squirts of throttle body cleaner to clean the IAC:

While you're at it, clean the throttle bodies too. They can sometimes get a teeny bit sticky:

**ViperTony** · 11-13-2013

I've been advised many times not to use carb cleaner to clean the IAC as it may damage the seals inside the IAC. MAF cleaner was recommended but I used throttle body cleaner. A wise Viper owner also suggest spraying a touch of WD-40 inside the IAC for good measure. I just went through this procedure. My Viper was stalling coming off throttle, idled rough. When I went to pull out the IAC I found that the lower bolt hole was stripped and the IAC was not sealed properly against the intake. Anyway, cleaned the IAC per the above procedure, re-tapped the stripped bolt hole and all is well now. Remember to re-learn WOT throttle after the PCM reset. As others have stated, if it wants to stall let it, it is part of the PCM re-learning process.