Idle Surge and Base Timing

[aspekt9]

I'm having some idling issues and I think timing issues as well. I want to set base timing on my car but I think it needs to be idling properly first. I'm running 272 cams and I would like to idle it around 900 or so. My problem is the BISS is screwed all the way in and my idle is at 1,000 RPM, but once the engine reaches operating temperature the idle starts surging between 1,000 and 1,400 RPM. I'm guessing I should fix the idle issue first before I try to time the motor? I have a FAIV block off, EGR block off, vacuum line delete, and I just replaced the ISC because before the engine wouldn't idle at all. I put in the new ISC and screwed the BISS in and it idles right at 1,000 until the engine is warm then it surges. What changes at operating temperature that would make the car do that? Can I set base timing while the car is surging at that high of RPM? If I take off the position switch green wire, the car stays at 1,500 RPM, as soon as I plug it back in it starts surging again.

 

[GRAVEDIGGER]

Sounds to me like you need to properly adjust the BISS screw. If you have not attempted to do so you need to give it a try. Here is how you need to do it.

1G BISS Adjustment

 

[aspekt9]

Okay so I grounded the plug at the firewall and grounded the diagnostic port pin 3 and once the car got to warmup temp it started surging. The weird thing is when I disconnected the ground from the diagnostic pin and just left the other one grounded to the firewall I noticed that the surging stopped and the car idled perfectly at 1000 rpm. Does this mean the ISC is garbage?

 

[LiquidX]

Have you at least done a solid boost leak test and then checked for potential vac. leaks?

 

[steve]

Without changing the ECU software you can't change the idle speed without forcing the ISC out of range and disabling the ECU's ability to manage the idle speed.

What are you using?

 

[Dizorganizer]

this sounds like a air leak, like vacuum or boost. i had this same problem mine was due to a vacuum line was off

 

[aspekt9]

I'm using Link, steve.

So I went out and set base timing. I let the car warm up, grounded the timing connector in link, it kept the idle stable at 1,000 rpm and i set base timing to 5BTDC. I then shut the car off, ungrounded the timing connector in link and started the car back up. It continued to surge, it would advance timing while it was going up to 1500RPM then when it jumped down to 1,000 my timing was around 8-10 BTDC, where it should be. So I think my timing is okay now, I just need to get my idle under control. I'm going to be checking the ISC coils when I get home and see if my ISC is the issue. I'm also making a boost leak tester and will check for vacuum leaks as well. Everything is capped off though so it would have to be somewhere in the piping.

 

[steve]

Check the ISC coils, make sure it moves in and out when you turn the ignition on, pressure test, look for internal ways for air to bypass the throttle plate, set the BISS, and if needed adjust the Coasting Fuel Cut in DSMLink since your running a higher idle.

 

[aspekt9]

I replaced the ISC with another one I had around. It was able to maintain idle a little better, I had to back the biss nearly all the way out to get it to idle good but it does stay around 900/1000 without surging. However, it seems it wants to die when I come to a stop and I need to blip the throttle a bit to help it out. My ISCPosition is also 120 in link which leads me to believe that I have a leak somewhere.

 

[steve]

My ISCPosition is also 120 in link which leads me to believe that I have a leak somewhere.

That's an indication that the ECU has tried to open the ISC up as far as it can to maintain the idle speed and can't.

Either the "new" ISC is bad or you have ECU problems with the ISC drivers or their circuit traces.

Tom and Dave or I can fix it if the ECU is bad.

 

[aspekt9]

So a leak wouldn't cause a high ISCPosition?

I had the ECU conversion done in order to run link. I've only put 120 miles since receiving the ECU back from them. I suppose the ISC drivers could have been damaged if the old ISC was bad? The new ISC I put in isn't really new and it's not the revised version, it's the brown one. I'll look at the ECU ISC drivers as well as test the coils. Also the O-Ring is missing I'm not sure if that would cause issues or not.

 

[steve]

If you had a leak the ECU would be closing the ISC down to drop the idle.
Yes you need the o-ring an if the ISC coils were shorted before it would blow the driver as soon as you turned the ignition on.

 

[aspekt9]

So if the drivers are not blown it means the coils are not shorted but they could still be bad. Either way I'm going to order a new ISC, I'd like a revised one. I should be okay driving it until Monday though, right?

 

[steve]

If you can live with the dieing.

 

[street2nerz]

Hi All!

Nearly Stock Setup ( For Now )
GST
125k Miles
4G63T
Mishimoto Radiator
Tanabe GF Sport Springs
************************

I have had almost the same issues as everyone else, and after dissasembly cleaning every single part to perfection, still had the annonying surge between 1k, and 18k. So after checking and double checking every last detail for leaks, squeeks, and vacuum, it hit me, "Throttle cable adjustment" )

After I set every aspect of the Air ratio, BISS, Cable PIN ( Near ISC , Screw ), PCV Valve. I loosened the two 10mm throttle bracket screws to allow it to completely be free, the Idle instanly hit 850, and has NOT moved since. I truly thought I was losing my mind over this. My ISC checked out at 30kOms, and everything, I mean everything was double checked.

It does jump like it's supposed to when turning on the AC to about 1k or so, but falls right back in line after the switch clicks off during cylces.

Everyone should check that cable from time to time, especially if you are sure all else is good, that cable can sometimes hold open the plate allowing too much air to pass, and the system is compensating in return. DO this with the engine running after full warm up. Re_tighten to least resistance. The cable will pull towards the throttle body a bit.

Hope this helps anyone! Thanks!

 

[steve]

Good reminder.

If you look at the FSM procedure for the BISS is tells you to loosen the throttle cable before trying to adjust the BISS and then the correct amount of slack to leave when you tighten the adjuster.

Everyone should have at least the pdf's for the FSM now, if not look in the Tech Forum FAQ's for the links.