This is probably a question nobody has ever asked before, and so I thought it best to go in this section. When you start your engine cold, and it initially revs up, is there any way to set that rpm differently? I notice my car starts up and revs to anywhere between 1500 to 1700rpm for a few seconds. Would a custom program be able to lower this rpm to say 1300 instead? Why does GM feel the need to have the engine rev this high when it's initially started? To me I think it could be very detrimental in extremely cold weather, and could shorten engine life.

I've noticed this more lately because my engine used to rev to 1500 on a cold start and come back down faster, but since I reset my computer a few weeks ago it now revs up a bit higher and holds up their higher too (I should probably clean the IAC anyways) But after watching the engine's behavior on a cold start a lot, it really got me curious as to why it needs to rev so high, and if anything can be done about it at all.

 

I'm afraid I dont have a definate answer to your question. Mine has always turned ~1500rpm right after I let go of the key but it stays there maybe a second at the longest before falling back down.

There is a "Idle RPM vs Coolant temp" table in the programing to help the motor warm up faster but I dont think it goes as high as 1500rpm. Even so it would only do it in really, really cold weather.

 

This should be posted on LT1 Tech, or "computer........" boards, not on Advanced Tech.

Moving to "Computer......."

 

hey Patman, a custom programmer can adjust your scold start up RPM.

 

There's a table for idle RPM, in and out of gear, depending on temperature.

Stock values don't get any higher than 1200 RPM, and that's at super cold temperatures. If you're revving up to 1700 when you start it, you probably have your throttle blades open too far and it's taking the PCM some time to adjust the idle air motor.

 

The problem is getting a little better, it only revs to 1600 on a cold start, but I should clean the IAC out anyways. Another problem I'm having is that when I'm slowing down, the idle wants to stay about 200rpm higher. So when I'm in first at say 10mph, it's running at 1100rpm, and when I brake it's pulling the car a bit harder. When I stop for more than 5 seconds, that 1100rpm idle eventually settles back down to about 600. Then for the rest of that drive, the idle is fine when I'm slowing down (it will then rev at 900rpm on those 10mph coasting sessions)

 

I now do not need to do this adjustment, as I had the car in the dealer for another problem and they found a vacuum leak on the line going to the PCV. They fixed this and it solved both the high start up idle rpm and the coasting down idle problem too. It now only revs to 1400 on a cold start, and the rpm comes back down faster than before also.

 

The problem of the rpm being too high as you slow down can be adjusted in the " throttle follower IAC offset vs mph.

Brian