Ive got a 97 viper gts, idle has been fluctuating from 550-650rpm when fully warmed up. also when you go to start the car, idle jumps to like 2200rpm then comes down only does this 80% of the time.. i smoke tested it and it has no vavccum leaks. people say the intake manifold gaskets leak, but no smoke came out of there. also i replaced the idle air control valve and problem still existed. also replaced the pcm with the updated software, didnt fix it. any help appreciated. car only has 20k miles
97 Viper Gts Idle Fluctuating from 550-650rpm
- Thread starter 97GTStx
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Paul Hawker
Enthusiast
There is a technique to sync your throttle bodies that often resolves this. Also a low battery can sometimes cause erratic idle.
uvbnbit
Enthusiast
have you ever cleaned the IAC (idle air control) motor? that may do the trick.
Is there a significant/custom reflash of the PCM or Is It the OEM updated software? If you have a bunch of mods and a totally reprogrammed PCM, attention to idle parameters is sometimes overlooked.
If that's not an issue for you then it's likely in the IAC as Chip suggests. You said you replaced it but perhaps the new one was "sticky" too?
If that's not an issue for you then it's likely in the IAC as Chip suggests. You said you replaced it but perhaps the new one was "sticky" too?
kratedisease
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Yes, this corrected my idle issue.
Glad it's fixed.
Vipers do idle quite low (just beneath the 750 rpm line) and the 96-99 with the 708 cam is quite lumpy. Coupled with the fact that most new Viper owners don't realize that the first line represents 500 rpm, some might think there is a problem.
uvbnbit
Enthusiast
Have you tried re-setting PCM (varying opinions on best way to do it) and throttle position too. That might help as well.
simple search ought to come up with results.
I prefer the "ground at battery" method. PITA, but that's what seems to work for me.
simple search ought to come up with results.
I prefer the "ground at battery" method. PITA, but that's what seems to work for me.
There are adjustment screws on the tb's. Driver tb should open a tiny bit before the passenger tb. If you do a search, there are instructions somewhere here on the board. Don't think it has anything to do with fluctuating rpm's though, but you never know.
You have to take your intake tubes off in order to the the butterfly valves. There are adjustment screws on the TBs in order to adjust the valves. Valves should open at the same time (driver a tiny bit before). It's pretty obvious once you have the intake tubes off and look at the throttle bodies. 
In the majority of cases, the throttle sync is done on the common throttle bar, leave the butterfly adjustments alone. To sync the TB's, just make sure the drivers side opens slightly before the passenger side/
You have to take your intake tubes off in order to the the butterfly valves. There are adjustment screws on the TBs in order to adjust the valves. Valves should open at the same time (driver a tiny bit before). It's pretty obvious once you have the intake tubes off and look at the throttle bodies.
