C6C6CH3vo

iTrader: (9)

Have this irrating idle problem that goes through a viscious cycle. It starts off at about 1100 rpm and after driving about 15 - 20 minutes works up to 1500 rpm, then after hard driving it goes into a hunting mode hopping up and down between 1500 - 1800 rpm just like a vac leak. When it gets this bad I key off and back to on then it fixes it and idles like 900 rpm - perfect.

But this isn't always the case, sometimes resetting the ignition results in 500 rpm, and sometimes the idle remains tolerable for a day and stays at about 1200 rpm. Logs are inconclusive due to abnormal readings in such conditions as the ecu tries to correct itself, but for the most part the AFR is respectful to the fuel and air so no unmetered air is getting in.

IAC is good, swapped a MAF, switched out the EGR valve, checked all vac lines... it is something particular to being temporarily fixed by turning engine off then back to on. What is it?

When it gets bad I have to shut off engine before I get to a traffic light to avoid frustration

Help!

C6C6CH3vo

iTrader: (9)

Tensioner cause this?

dubbleugly01

iTrader: (24)

how many miles? What mods do you have? You referenced a/f, do you have a gauge? Could be your front 02 sensor starting to give it up.

barneyb

Once the idle gets so high fuel is cut off. Hence the bouncing idle.

I'd say it has got to be either the biss or isc.

C6C6CH3vo

iTrader: (9)

Thanks,

55K miles, moderately stock except for cams, water-methanol (20k miles), and LC1, ECUFLASH, and several other minor mods, but nothing has changed since the problem started except for cooler weather and several more psi of HP.

When the front sensor goes, what type of readings does it do? The only SES code I get is for idle too high.


Thanks,

It is not the idle stepper, Iv'e already checked and replaced that. What is a biss?


If my belt tensioner is acting up and putting less tension on it the intake cam would delay when less rotational force can take up the slack - like at idle. would this cause idle problems? I am guessing the when the eng is turned off the tensioner will extend and belt is tight abain so this is the reason it idles normal after ignition off/on

I guess I need to find what the symptoms for a bad tensioner are first

evo828

BISS is the Basic Idle Set Screw - the screw on the throttle body which you use to setup the basic idle (but then the Idle stepper tries to manage as per you tables in ECU). I do not think this could be the cause of your problems. Have you tried the idle reset and learning prcedure. With the engine warmed up, Disconnect battery for couple of minutes, then connect, start and let idle for ten minutes.

C6C6CH3vo

iTrader: (9)

Thanks,

Yes it definately isn't the set screw, and I really doubt problem is related to anything with the TB since cleaning and rebuilding it changed nothing.

I haven't tried waiting ten minutes yet, I'll give that a try right now. I noticed it takes about ten minutes after battery reset for the feedback O2 to kick out of 100% though, just never waited ten minutes

barneyb

There was an active thread right here several days ago concerning meth and the isc. Seems the meth can ignite in the manifold and toast the isc.

C6C6CH3vo

iTrader: (9)

The methanol I use is not flamable because it's 50% water, not to mention I stated three times in the thread already that the ISC has been removed, inspected, and ohms checked.

I reset battery and idled for 15 minutes and it idled fine for most of the day enduring 3 WOT applications. Then I hooked up my laptop did one pull, still good, then did a nice hard 2nd gear pull hitting 31psi - idle bad (1000 - 2500rpm hunting), ignition off then imediately on and its good again.

DTM

iTrader: (4)

How about the EGR control solenoid?

C6C6CH3vo

iTrader: (9)

Iv'e checked that. Removed it and did the test per service manual, it was good. Just as I said in the first post.
Someone knows whats causing this problem, please respond

DTM

iTrader: (4)

I didn't mean the EGR valve itself. I meant the actual solenoid behind the manifold. I wasn't clear...well I'm sorry it didn't help, good luck

C6C6CH3vo

iTrader: (9)

Thanks, when I meant EGR valve, vacuum linesI was referring to the valve, solenoid, three lines and tee. I took the whole assy out hooked up when I replaced the valve and bench checked everything. Even though the valve was good I replaced it for the hell of it because I had a spare.

The BISS when turned all the way down will decrease the symptoms, but idle is too low when everything is working properly.

If this is the trade off for HP with stock parts, I can live with it, I just want to make sure it's nothing like a tensioner going bad and would retension itself after engine stops. Anyone know what effect delayed intake cam would have on idle?

Evo8Emperor

iTrader: (12)

I know my car is lopey with HKS 272's not sure what your running. Normally it will die once when its cold and then on the second try it stays running. Other than the idle dropping sometimes i dont find it erratic. I believe its just the cams. But then again what do I know but as far as the car it runs fine.

C6C6CH3vo

iTrader: (9)

My problem isn't idle dropping when it's cold due to BISS turned down, my problem is a random RPM idle surge between 1500 - 2500rpm that will reset to normal once ignition is off/on.

The surge occurs after a high boost application

I turned the set screw down to take the edge off the problem, but when its working properly the idle will be too low - a trade off.

Reading thuroghly tells what question I have

Thanks