Outside temperature determines idle?

[crunchymilk]

Ok so I have a full bolt on 96 GST. The weather here in South Texas has been 100+ or in the area for quite some time now, and my idle has been exactly what I put it at in dsmlink (1050 rpm) It's been working fine. However, we recently experienced a cold front and my idle shot up to almost 2000rpm. Even with a warm engine it does this, and nothing i can do, including with DSMLink can lower the RPM, sometimes it goes down back to where I set it on it's own, sometimes it does not. I understand cooler air = denser charge, but I can't see that being responsible for a major idle discrepancy. Any thoughts?

Also, you northeners are lucky bastards. I thought my car was pretty fast, but after this cold front, HOLY SHIT, I can barely keep it under control. 60 degree weather > 100 degree haha.

 

[MrBoxx]

Possibly due to the Fast Idle Air Valve on our cars. As I understand it, during colder weather, it opens up the throttle more to let the car heat up faster. As coolant passes by the FIAV, it slowly closes the throttle back to normal operating position. In Michigan, during winter my idle will be at about 1500 or so, then slowly drop down to 800-950 after a few minutes. There's a way to bypass it, and since you're in Texas, it might not be a bad thing to do. In colder states, it's kind of a good warm-up feature. You could try disabling it and see if that makes a difference.

 

[crunchymilk]

thanks, good info there

 

[92 GSR-4]

Are you aware that the idle on our cars is electronically controlled? You may spend 5 minutes resetting the ISC to calibrate your idle and solve everything. Just put the engine in diagnostic mode for Idle baseline (DSM LINK will do this on my 1G, pretty sure 2G is the same), and turn your biss screw to your desired idle speed. This will let your ISC move forward or back to better manipulate the idle.

Your ISC may not be zero'd out, meaning it cannot adjust as far as it needs to, in order to achieve the correct idle.

By the way, why you are idling at 1050 is beyond me, but you may change DSMlink back to stock (750), then calibrate your idle and move it back up.

 

[crunchymilk]

Anything below 850rpms and my car shakes like a freakin earthquake. This happened right after the 4 prothane motor mounts so I would assume that's the problem. I'm thinking the ISC motor itself may be a problem, because anytime I coast out of gear it idles at like 1600, then after 2 or 3 seconds at a standstill, it goes right back to 1050. I have no clue about this.

 

[92 GSR-4]

Have you tried to re-calibrate the ISC yet? It's easier than stock if you use DSMlink, really.


Try it and post what you find.

I know about the prothane motor mounts, I had a set, and swapped them out for the stockers again, too much vibration, so I know where your coming from now. To help that, you may want to swap the REAR one, under the intake manifold. Thats where most of the vibration comes from on a 1G (i assume the same on 2G). If you keep the Tbelt mount and the passenger side tranny mount it'll keep the engine from twisting, but in a FWD i can't really see why you have them. My AWD ran just fine without them, mid 12's on a 16G all day long on pump.

By the way, you can also test the ISC with a multimeter. The std. resistance in the coils on a 1G is 30 ohms. Check that out, they go bad all the time.