Boombox

****UPDATE: It was a wiring issue****

My 2003 Evo 8 has a cold idle problem I can’t seem to fix.
No check engine lights

One day the car wouldn’t idle without having to keep your foot on the gas.
I had this problem before and it was a dirty IAC. Cleaning the IAC didn't fix my problem this time. I bought a brand new OEM IAC ($330 ) and reset the BISS with evoscan.

Now the car will idle and run great when warm, but I have to give it gas when it’s cold to keep it from stalling.

I was told it takes a while for the car to learn idle, but it has been months.

The car is a 2003 Evo8. The only engine mods are intake filter, uicp, and a highflow cat. It idled fine with these mods before. The car had boost leaks on the throttle body shaft seals and a big leak on an intercooler pipe weld. These have been fixed and there are no boost leaks now. As far as I know the car is not tuned. I believe the previous owner put on a Walbro fuel pump. Can they cause this problem and still run well when warmed up?


The IAC doesn’t look like the original. It is the evo 9 style. I read that they are interchangeable. Is this true? I still have the evo8 throttle body. I read that the evo9 throttle body doesn’t have a heat flapper that the evo8 has. Should I remove my heat flapper?


I replaced the coolant temp sensor and it didn’t help.
I even took the intake manifold and throttle body off to clean them, but no luck.

I have evoscan and ecuflash. If there is anything else you need to know to then please let me know. Sorry if this is hard to read. Just wanted to give as much info as possible.
I’m stumped. Any help is greatly appreciated.

evo8vz

adjust your iscv step possibly give it more timing on idle

Boombox

I'm very new to EcuFlash so please bear with me.
Do I adjust the iscv steps in the "Desired ISCV initial step position" tables or the "Idle Stepper lookup table?"


Also, my Min Coolant Temp for Closed Loop is 7*C. Does this mean my car is running in closed loop all the time after 7*C?
Is this ok? It seems kinda low to me but I'm still learning about open loop and closed loop.

Boombox

I adjusted the min coolant temp and nothing happened so I guess that has nothing to do with cold start

I haven't adjust the iscv steps yet but I was watching them while the car warmed up. When it's cold and barely running the steps are at 120. When it's fully warmed up(180*F) the steps go from 0-5.

Also, I was hoping there was a fix for this problem that didn't require "tuning." The ecu hasn't been messed with before. It doesn't make much sense to me that a car would require tuning to get it to do what it's supposed to do from the factory.

Evo8cy

Since your ecu has not have any of its idle related settings altered before, since you are not running bigger injectors or different than oem camshafts, do not change any of the idle related settings. Make sure your fuel pump is getting the right voltage and that is working as it should, and simply adjust the biss screw a bit at a time until the idle becomes stable.


The issue is not ecu related. If problem insists, replace idle control valve with a friend's to see if the problem goes away, if not report back here to see how we can help resolve the problem.








Marios

barneyb

The car always starts in open loop. How quickly it goes into closed loop depends on the condition of the oxygen sensor.

When an engine idles fine warm but stalls cold think vacuum leak. A boost leak test should find it.

Boombox

Thanks for the replies. The car doesn't have any boost leaks.

I can't seem to find how to check the fuel pump voltage.
What is the right way to do it?

barneyb

How long it takes the idle to relearn is about 10 minutes.

You say there are no vacuum leaks. Well somewhere between 9 times out of 10 or maybe 99 times out of a 100, with the symptoms you describe, it is a vacuum leak. Pardon me for being a little sceptical.

The other possibilities are a purge valve problem which should set a DTC, a stuck open or aftermarket PCV valve, a EGR valve stuck open which probably won't set a DTC or a bad tune it the ECU has been reflashed. That's it. It seems unlikely a weak fuel pump would only cause problems at idle. But to check I would suggest pressure rather than voltage.

What would be nice to know is what the fuel trims are doing. If the engine computer is correcting for a lean condition you probably have a vacuum leak.

Boombox

I don't blame you for being skeptical at all. It would definitely seem like I have a boost leak but I can't find one when I do a boost leak test and the system seems to not bleed off any pressure.

I believe the STFT was around 8% and the LTFT was 2% last night when I was using evoscan to watch the isc steps.

Evo8cy

Boost leak is not your problem, serious boost leaks create rough idle, but the car still idles fairly ok, a minor boost leak will not affect idle. Most evos out there leak through the throttle body seals their whole life but they idle just fine. The reason I told you to check the pump is because there might be less voltage going to the pump during its 0.8 low voltage operation during idle mainly due to corrosion of the wires and or connecting plugs, check the passenger footwell side also for any signs of corrosion on the wire going to the pump. Pull the plug on the pump that feeds it with power and use a multimeter on it to read voltage.






Marios

Boombox

I couldn't find any corrosion on the wires on the passenger side or the driver's side for that matter.

I pulled the plug on the pump and got 5.3volts when probing.
The car is warmed up though. Should I try again when it's cold?

roni4g63

iTrader: (1)

The car goes into open loop everytime you go WOT

Evo8cy

5.3 volts is too low, it should atleast get 0,8v, when everything is in check, it gets between 0.8v-0.9 volts and 12v-13v when you put your foot down along with open loop as mentioned on an earlier post. During idle, and cruising, you are running on closed loop.



Somewhere along the line you have loss of current, check all ground wires, both in engine bay and under the carpet and back seat. Also check the pump resistor pack in the engine bay, for corrosion, check/clean its plugs. And if you can provide a video of the car on idle , it would be helpful. The idle control valve should get 0,5v, I would also check that also, and try a friend's valve to see if it corrects the problem.


Also have you tried adjusting the biss screw to see if idle stables out.










Marios

Boombox

I'll upload a video tomorrow and check for corrosion.
Unfortunately I don't have a friend with an evo. Maybe I can find someone in Austin willing to help.

Liqquid

You mentioned the leaky shaft seals and IAC were replaced, I would look closely and make sure nothing fell down into the holes that could clog up the fast idle air valve making it act like the car is warm already.. this part is hardly mentioned on here, hard to explain so I copied from this post:

"The second mechanical idle control is the Fast Idle Air Valve (FIAV) The FIAV is a plastic/wax plug that blocks off a passage that allows airflow to bypass the throttle plate. when this plug is cold is shrinks and blocks less of the air passage and more air bypasses the throttle plate raising your idle, as the coolant heats up, the plug gets warm and grows blocking more of the air passage so less air is bypassing the throttle plate and your idle goes down."

Taken from here:


https://www.evolutionm.net/forums/la...ypass-mod.html