Hi All,

I have a strange idle issue looking for some help from the community.

When i start the car it idles great at 1000 rpm (programmed rpm in ecu). Proper AF at 14.5. Once the car is hot (operating temp), the idle shoots up to 1200-1600 rpm, AF at 14.5-13.1. The ECU will see this and correct it down to 1000 rpm, then again it starts over again. Eventually the ECU will adjust aggressively resulting in stall/lean condition until it corrects again to 1000 rpm then it shoots up to 1500 starts all over again. Never ending cycle.

I've replaced/checked the following. All new hoses no vac leaks, brand new rebuilt throttle body, fiav removed and blocked off (no isc), properly adjusted tps-idle switch, bov not open at idle, swapped mafs, checked tuning in ECU, battery voltage 14.0, brand new throttle cable properly adjusted, no gunk (new motor-intake manifold). Not sure what to do from here...very frustrating.

Notes:
I'm running the flashable black ecu with Ceddymods with 850cc injectors, 255lph hp fuel pump, -6 an fuel filter to rail, aeromotive a1000 set properly. evo3 big16g.

Any help is welcome, hitting my head against the wall here.

Forgot to add, the egr is also blocked off, and the 02 sensor is working properly (also new).

The ISC was put there for a reason, why did you remove it? It's designed to compensate for this exact issue you are experiencing.

Unless you set idle switch on link though, no?

What is Your ECU correcting Idle with if it doesn't have an ISC?

You can simulate it using link. Assuming he's got it.

That's just for the switch isn't it? I was refering to what is the ECM controlling to make it idle..ie it can't control the TPS or BISS screw. So what is limiting air flow to control it?

Must be in the program? I use the simulator and unplugged the ISC to prevent it from ever damaging the ECU.

Because the fiav wear out, I don't want to pay $250 for a new one, it may compensate for it, but that doesn't solve what is causing it...

Not using link, as mentioned using ceddymods evo program.

Woops..

Your car is still getting air witch makes it's Idol serg or it dose not know that it should be idoling. Thing with these old cars is Link will help you LOG and find these little problems that drive you into maddness to no end

more info on your set up will also help

What's on the Ceddy chip for idle? If it's just like stock then maybe not having the ISC really is the problem. Have you tried adjusting the BISS to find a stable idle, even if it's not the 1000rpm that the chip is set for?

Double check the idle switch and make sure it's not holding the throttle plate open at all.

Was the rebuilt throttle body to solve this problem? If not, check it over, make sure the throttle plate closes properly.

I know you said new hoses no vac leaks, but did you do an actual boost leak test? Again with the throttle body, maybe the seals aren't right.

History on the car - did this problem just happen out of nowhere or were there a bunch of mods thrown on and which mods?

Rpm value is 1000rpm on ceddymod. The car idles great until it hits operating temp..yes I check and adjust biss it makes no difference it will still increase to 1200-1600 rpm.

I checked the idle switch its not holding the plate open if it was this would happen on cold starts too. This problem occurred with my stock throttle body as well, so I know the new one isn't at fault.

Boost leak test showed no leaks, its been happening for more than a year now. I've been busy getting it driveable this is the last issueto fix.

This also happened on my stock motor..

thanks

What more setup info should I supply? Think I mentioned everything.

I have evoscan it can log everything the ecu sees..everything is checking out normal. Whats bugging me is, runs great until hot then goes crazy.

Hmm, doesn't the FIAV serve to actually lower the idle when it gets to operating temp?
Without the FIAV, I think you would need to turn the BISS up for cold start and then once at operating temp the idle would end up even higher, to the point where you hit surge as the ECU tries to compensate. I'm assuming you didn't run the FIAV/ISC on the old or new throttle body. If that's the case, I'd try a perfectly stock throttle body next.

I believe youll need your ISC to be the idle brain as your temps warm up. The simulator would simulate the ISC, which doesnt seem like your program is set to do.

ECM link has the fast idle isc position adjustment based on coolant temperature.


I think you need it.

The old tb did have fiav/isc same issue. I removed them on the new tb to simplify the setup.

But I don't have any issue cold or warming up, its when its hot it goes nuts.

Short term fuel trim..

Darvesh,instead of wasting time here, all you need to do is install an ISC to fix this.

The FIAV delete alone does not mean you can run without an ISC.The FIAV does not control idle directly, I would really like to know you where you got the info to assume that it does.

You learn something new everyday. I always used ST and LT as a diagnosic tool, But I guess if diesels can control idle with injector timing so can gas.

Do you have the port at your T-body that the EGR thermo valve used to plug into.
Only thing i can think off that would change at operating temp

I have (3) ports on the tbody. Two are blocked off and one is run to the boost gauge/boost controller with a T fitting.

Oh yes 2g sorry didnt look at that first.