unstable idle

[blizz99]

My has another problem. When my car is in neutral and is just idling, it jumps back and forth from around 1000rpms up to around 1300-1400 rpms. It jumps as a constant beat, kind of like a heartbeat. I was told this could be due to the hks cams. Anyone know if it's really the cams or what it actually is?

 

[FusionTalon]

well it could also be the Idle speed controll motor, i belive thats the name for it, is probly getting stuck and u need a new one, i forgot the depth of the problem since ive been out of the dsm scene for about 2 years... i belive this is a common problem...

 

[payup]

Looking at your mods you dont have any tuning stuff. It sounds to me like you need a good tune. Check this site alot on idling problems http://www.vfaq.com/index-main.html

Good luck to you. And keep boostin

 

[Heavy-D]

One of my friends fixed the same problem on my car. He adjusted something, I'm assuming it was the idle control, and I watched the tachometer until he got it down to like 750 to 800rpm. It used to do the same thing, starting at 1000+ and revving up to 1500 and bouncing back down.

 

[jaredgsx]

It could also be a vac leak. I had one and it did the same thing.

 

[blizz99]

One of my friends fixed the same problem on my car. He adjusted something, I'm assuming it was the idle control, and I watched the tachometer until he got it down to like 750 to 800rpm. It used to do the same thing, starting at 1000+ and revving up to 1500 and bouncing back down.

I tried adjusting the idle. It still does it. If I adjust the idle to anything below 1000k rpm, it wants to stall out.

 

[gridlyne]

It sounds to me like Idle Surge which from what I understand its something that happens on these cars. The exact cause is debatable but many people have taken shots at explaining it. Im trying to search through my favorites for a site that explained it really well. Ill post that up as soon as I found it.

 

[Ethen87]

i had the same problem with my car........... there is an idle control screw the must be tightened or it might have fallen out.

 

[alex]

Its called the BISS. (Base Idle Speed Screw).

http://www.vfaq.com/index-main.html

DSMs are known for their little idle surge they doo.

 

[femmeDSM]

If you adjusted the BISS and are still having idle problems, you might have a worn BISS o-ring. Slowboy racing has a replacement (in fact, if your BISS looks bad, they have the whole assembly, so you can just swap out the whole thing, if that makes you feel any better).

Also, I assume you read the V-Faq on adjusting the BISS, as you need to ground a terminal on the ignition timing plug behind the battery, among other things...
If you haven't seen it, here's a link to that article: http://vfaq.com/mods/BISS-1G.html

Also, you might want to check your ISC motor. You can check it with the unit on the car, but if it's bad, you will need to remove the throttle body to get at it. http://dmtalon.v8eaters.com/ISC.html

A good tune up, new plugs/wires/air filter and a SeaFoam/MCCC treatment wouldn't hurt, either.

Good luck

 

[95GST_OBD1]

Im currently having the same exact problem in my 2g gst after a **fresh** motor build. I'm going to follow the tips posted here and do some tuning to the BISS and im going to check for vac leaks. I've eliminated the egr and evap canister so that might have something to do with it. Ill see if this does anything and ill get back with some results..... hopefully. anyone else have any suggestions b4 I get to work??

 

[jeffo]

Idle surge can also be caused by the FAIV bypassing too much air. Both my GVR-4's had a hyper-active FAIV, so I ended up JB Welding the FAIV section shut. But, I live in Florida, so that's not a good option for most people. You can also readjust the BISS by popping the freeze plug out underneath the FAIV and turning the screw in a bit. If you have removed the coolant loop through the throttlebody, but still have a functional FAIV, that will also cause surging issues, since the FAIV never warms up completely.
The other thing I have found that often causes idle surge is a non-functional Idle-Position Switch on the throttlebody. On 1G's the switch often becomes unplugged, or gets out of adjustment by someone trying to use it as an idle-stop. It also becomes an issue if you swap to a 1990 ECU with a 1991+ DSM, or the other way around, because you need to swap pins 6&14, and one of those wires is the idle-position switch. On 2G's with a 6-bolt swap this is also often an issue, because the idle-closed switch is integrated into the 2G TPS. When guys swap the 2G TPS onto their 1G throttlebody they often don't calibrate it properly, or check for continuity between pins 3&4 of the TPS when the throttle is completely closed. A logger makes all of these tests MUCH easier.
keydiver

 

[ragdollstalon]

your IAC could be trying to compensate for too much air and ends up making its own rythmatic beat and the motor pulses. basically its trying to fix itself evertime it idles up to down and overcompensates.

basically unplug the idle air controller and see if the pulsing stops.

 

[95GST_OBD1]

I recently replaced the biss screw o-ring and plug, but still same issue i'm assuming that it is the iac sensor because the beat disappears when unplugging it like you said. although the surging is only happening when the car warms up after idling for a good minute or two. it will surge every once and a while, then the rhythm will speed up and stay constant. I'm still doing some work on it so when I get the right fix i'll post again. Any other suggestions???

 

[audiomaster1990]

yea dude, if you unplugged your air sensor and it stopped, thats it. get a new sensor, or if you dont feel like paying 180 bucks, get a gm sensor and the adapter, youll be better off that way anyway

 

[Kickerbeast]

You can get one at Advaced Auto for $75 I think. I know it is less than $90. I'm getting one this weekend as my surge is getting worse.

 

[95GST_OBD1]

TPS replaced= no idle surge.

problem solved