In open loop my car idles great! but as soon as I hit closed loop all of a sudden the idle drops and becomes very unstable I get a mis on cylinder 7 and after a little bit the computer I guess sees the lower idle and bumps it up (you can hear it rev a little).
After that it idles ok (no mis) for a little bit and then the scenario repeats itself again.
Things I have checked:
Injectors, I have removed all of them cleaned them out and they seem to spray fine.
Plugs/wires I have visually checked these and they seem ok.
Help please!

 

you can swap injectors and see if the problem moves.
how do you know that #7 is missing?
with a plug wire the problem should be there beforeclosed loop too...

 

May be your distributor or a throttle position sensor. Is it showing a trouble code?

 

I guess it could be the opti, but why only in closed loop?
No codes other then the air pump egr and rear o2's.
I autotapped it and it show cyl 7 missing when this happens.

 

The only in closed loop means it is a sensor or a false input to a sensor of some sort, but all of the sensors would effect all CYLs thats why I want to know how you know #7 Is misssing

 

how does autotap detect aindividual cly Miss? you dont have 8 o2s or 8 knock sensors is it going off of spark lines?

 

It could be doing a cyl kill / RPM drop test.... did you swap injectors. Are LT-1 injector drivers paired?

 

I did swap injectors, no difference, gonna change wires today.

 

you know what, now that I think about it it would have to be doing a RPM drop test, thats the only way I can think of it determining a single cyl miss with those imput sensors, in that case, it makes sense that the IAC may controling the idle in open loop may mask any RPM drop... does it have an option to perform the test at a higher RPM? Or disable IAC? if so you may be able to get it to do it in open loop. in which case it could be a plug wire. OR just change the wires....

 

Not sure what replacing plug wires will do? If it is closed loop only then i would spend/look elsewhere...

Like o2s, MAF, and for vacuum or exhaust leaks. You really need a scanner, or find a friend with one.

 

I have a scanner!
That's how I know Cyl 7 is missfiring.
The o2 MV in bank 2 sensor 1 drops to like 50's when it idles like crap and after it rev's itself back up the o2's are at about 800 MV.
I have replaced my pass header gasket about 2 weeks ago and I used stage 8 bolts since they were loosening all the time.
Help!!

 

The OBD-II PCM detects individual cylinder misfires by comparing the CKP (crank position sensor) signal pattern to a known pattern for the engine. When the tiny accelerations and decelerations of the crankshaft do not match the programmed pattern for the engine, it indicates a misfire.

94 and up injectors are "sequential".... they fire one at a time, in the correct sequence, as determined from the low resolution pulse pattern from the Optospark. 93 injectors are "batch fire".... all four injectors on the bank fire once each crank revolution.

What do your long term fuel corrections (BLM's) look like for Cell 16? Do you have an AutoTap data log of the engine from startup/open loop through transition to closed loop, and the poor idle period.

 

I dont want to hijack the thread, but maybe you can help out.

When my car is in park it idles OK.. When in any get or under load, its crap. SES flashes. All the plugs are change as is the opti. Wires, from what I can tell, are ok.

Took it to get it scanned and it said there was a problem with the crank position sensor. Well, when I pulled the crank pully to put the opti spark in, I moved the crank a bit, but didnt think anything of it since the cam moved also.

So, could the CPS really be causing all of these problems, or is it just detecting a misfire some where?? If there is a misfire, what else could it be either than coil, plugs, wires, or opti???

 

I was having the same problem. Turns out No 8 plug had spark jumping from the plug boot to the heat shield. I thought it was a closed loop problems as well. In my case the spark jump would only become present after the wires/manifolds heated up.

 

OK some follow up on this.
I replaced the plug wires, no change.
Then I tried something a little different, I switched the o2's. Not just put the right one in the left header etc. I crossed them.
I put the left extention into the right header and vice versa. So the following is what happened:
Bank 1 o2 was hitting low 50's when the idle dropped and cylinder 4 starrted missing.
WTF is up with this?
I guess the only thing it could be is the harness going to the pass o2. Any other guesses?