advanced idle surge help

[emo1010]

Ok, here is what I have done and diagnosed so far.

Did boost leak test and fixed all of leaks that I can find.(used the soapy water method) Bov is still leaking a bit but is recirculated. This did improve it some, was surging around 2k now down to 1k to 1.5krpm

During the rebuild of the throttle body the ISC tested fine and set TPS.

I did a compression check today, 150, 145, 145, 150. Engine operating temp, throttle open, aprox. 4 rev.

The things that are still questionable that I think maybe causing it.

The wiring to the o2 sensor is fubar, sheathing falling off, corrosion on wires ect. I remembered reading this:

1. The idle switch is depressed (foot off the gas)
2. Too much air is getting through the throttle body (ISC stuck open)
3. O2 sensor registers lean mix (too much air)
4. ECU adds fuel to achieve correct mix
5. RPMs increase due to increased fuel/air supply
6. At 1500 RPM the ECU goes into decel mode and cuts fuel (*)
7. With only air coming into the engine, the RPMs drop rapidly
8. At 1200 RPM the ECU turns the fuel back on
9. Goto 2.

Could the problems with the wiring cause this with out throwing a code? I know I need to fix this anyway and have a lc1-1 on order that i am going to wire in to simulate narrow band and eliminate the bad wiring.

It has been surging for a couple weeks and the only code it has thrown was two days ago it threw a temp sensor code.

I'm just thinking out loud/typing. Any thoughts, help or advice is appreciated

Thanks
Eric

 

[92AWDHX40]

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge)


this may help too.

 

[emo1010]

More testing after i repaired the o2 sensor wiring.

I found that my o2 sensor is cycling between .03v and .065v. Which from my understanding is the cycle should be between .10 and .90. In my mind that seems like it would be so lean that it wouldnt even run. Replaced the 02 sensor, cycling better but lean like .1v to .3v.

I checked the ground for the sensor .5 ohms from wire to the battery.

Still need to check the wiring for sensor to ecu

But regardless of that the new sensor is showing lean.(im testing it at the sensor with a multi meter)It is reading lean.

The car is a stock auto with stock 390 injectors. When i bought the car I noticed it had a rebuilt ecu. Would it be super lean if it was a manual trans ecu with 390 injectors? Now that i think about it when i pulled the plugs to do a compresion test they were really clean more on the white side that eggshell colored and almost no carbon build up on them. what i would consider reading lean.

Any thoughts from people who know way more than me?

BTW: i re did my boost leak test and the system is tight. I get a little past the rings and the BOV and thats it. temp sensor was replaced also and no more codes.

Eric

btw the LC-1 fell through and just did a stock o2 sensor and fixed the wiring.

 

[92AWDHX40]

Did you check everything off on that list, could be a throttle body issue, isc, even i learned a small leak can cause an idle issue, i had a lot but fixed them when i did a boost leak. Still after that i found a few more since i added my fmic, but link really helped diagnose my idle issue, elimnated that stock switch.

 

[emo1010]

The only thing i have not done is the seeing if the isc moves smoothly.

 

[92AWDHX40]

Test the isc DSM ISC motor testing & Replacement - YouTube

 

[emo1010]

As I stated in the first post, I tested the ISC meaning I tested the coils. I did not pull the isc out and plug it back in and cycle the key to test the how smoothly it moves in and out like it says to do in step 5.

I did how ever just go out and do that and seems to move fine. I'm banging my head up a wall here.

 

[LiquidX]

Do you still have your FIAV hooked up (coolant lines)?
I would recommend the MTXL over the LC1 as the LC1 is an old model now. However, having the smaller injectors will run on the lean side if the ECU is expecting a larger injector.

 

[emo1010]

coolant line are hooked up.

I went out and triple checked my work.

EGR: it is blocked off and all the emissions vacuum lines have been removed and blocked off. The vacuum lines consist of one to the fpr, one to the bov , one for the brake booster and the pvc hose.

ISC: The coils test between 30 and 31 ohms, I pulled it out of the TB, cycled the key and it seems to function smoothly and correctly. I previously rebuilt the TB and thoroughly cleaned the TB.

Boost leak test: I isolated the piping up the TB and it was not leaking. I then retested the complete system. The only air that is escaping is in to the crank case past the rings, though I’ve read that it can go past the seals in the turbo and pressurize the crank case too.(is that true)? I guess I need to get a leak down tester to find out for sure. Would blow by cause idle surge or air past the turbo seals cause it? I would think not.
I also did the oldschool trick of spraying parts cleaner on all the connection of the intake and the idle never changed.

That leaves FIAV, do they really go bad? I have been working on dsm’s since ’99 and I have never had a FIAV go bad or have I ever heard of a buddies go bad. I live in south Texas I guess I could just eliminate it.

 

[LiquidX]

An improperly adjust FIAV will cause surge since the spring assembly is not sealing a tiny hole which will allow air to bypass the throttle plate.

http://www.dsmtuners.com/forums/articles-intake-exhaust/391977-free-fiav-block.html

I don't know if I noted in the write up but seal the freeze plug with RTV when you knock it back in.

 

[emo1010]

Ok, it was the FAIV. I guess the moral of the story is to trust your tests. I was convinced I was missing something weird. Thanks for all the help!

Liquid thanks for the artical on the free block off, worked perfectly.

Eric

 

[LiquidX]

You are welcome, glad it worked for you.