Idle issue
 

hey guys,

My '05 is doing some strange things at idle, the idle is bouncing from 850 to 1.5k or so when I let off the gas.....

And before you say it, No, I'm not VTA... I have the stock DV, my mods are o2/tbe/mbc.

the boost has been solid at 21.5, but with the colder weather there's some creep... I'm only worried about the idle right now...........

This all started after my exhaust install, but the same day I adjusted the idle down b/c my car idled at 950-1k since I got it... I was trying to get it to 850.

I've tried to adjust it back with the idle set adjustment screw, but it seems to want to "surge" anyways.

It has always stopped surging if I turn on the defroster..... until tonight when it surged anyways.

If I stop the car and idle for a minute or so, it stops.


I'm going to get some cleaner and clean my maf now, and the throttle body, as I've seen a dirty TB cause this on my old car.

Any other ideas? Search showed everyone w/ this trouble was VTA or cams.

look for a vacuum leak..... that would be my best guess.... and vta won't cause that......... also you might try resetting your ecu (disconnect the battery and step on the brakes for like 10 seconds to drain all power that might be left in the electrical system, then reconnect the battery and start your car up)...... those are my simple ideas.....

fixed!

I popped off the pipe to the throttle body and gave it a good cleaning with stp tb cleaner.... put it back together and started it up.....
It was idling at 1500!

It was stable so I backed it down to 900, looks like the surging is gone now, it's rock solid.

It appears that maybe there was something in the idle air pathway restricting the airflow, and as soon as it got outta there the idle went way up and stabilized from more flow.
Anyways, thanks for the reply!

You were getting idle surge from hitting the coasting fuel cut limit. That means the idle was more likely trying to go too high, not too low. Odds are something was holding the throttle plate open slightly if cleaning it helped. One thing to watch out for is the FIAV though, you generally don't want to get any cleaning solvents into that, and the holes are at the bottom of the opening, making it nearly impossible to avoid unless you cover those holes. It's also worth mentioning that the BISS screw is not for adjusting idle speed, it's for adjusting ISC position at target idle speed. So if possible get a scantool or logger on there that can read ISC position and recenter it. The factory manual may even have a procedure, I haven't checked personally. On some cars there is a pin you can ground to force the ISC to center, then set idle speed with the BISS, etc.

you know what, I think I remember doing something like that on my friends dsm now that you mention it.... damn I wish I would have remembered!

my evoscan has a row for ISC steps, I wonder if I can use that to reset it, I'll have to read up