Midnight 85

Back again and still fighting an idle issue but now it's a different problem and there are two of them. 85 L98, 383, super mild cam, 1.6 roller rockers. 52 mm BBK tb, long tube headers w/ true dual exhaust.
The car starts right up but the idle starts coming down right away, after it drops down then it starts going up and down like a yoyo, sometimes even dying. Once it's warmed up a bit it idles like a champ at 730 to 770, target idle in the chip is 750. Then when I drive it the second problem starts, it will not idle down correctly, it WILL idle down to the target range but only after sitting for a minute or more. In stop and go traffic it always takes this long to idle down even if I have only driven a block. It also wants to idle around 1000 rpm when it's in gear and rolling along, it will not idle any lower until I stop. All the minimum air idle settings are set, the tps is in perfect condition and the IAC is brand new. Timing is 6* with est disconnected. Vacuum leaks have been ruled out a long time ago. It's not a big deal, just irritating.

jsup

I just had exactly the same problem. Turned out to be injectors. According to Corvettes of Westchester, when the injectors go, you run the risk of killing the ECU.
Check the injectors.

BTW, I also installed a new IAC. DId nothing.

coupeguy2001

check your evap cannister purge valve. sounds like it may be falling apart or ingesting charcoal granules.
It's purpose is to recover any fuel vapors. if it is intermittantly sucking vapors de to vibration on the check portion, it might add vapors that are combustible intermittantly, and cause the surging or idle float.
also, try unplugging the electronic spark control module while it's running. if it smoothes out, the computer has fallen back on the limp home default timing rate schedule.
If it smoothes out, then it might point to a distributor module, or a poor ground for the coil, or something like that

Midnight 85

I hope not, they're pink tops from five-o-motorsports with only a couple thousand miles on them. Guess I better get the ohmmeter out real soon. Thanks for the input.

Midnight 85

Thanks coupeguy, I'll add that to my list of things to check.

jsup

Please post the results. It helps us all. Thanks.

Midnight 85

You can be sure I will.

steve40th

Do you have the original throttle body. I had BBK before, not the BBK/Edlebrock, and I always had it idle badly as the throttle body blades werent machined very well and it stuck allot.
I would try to put the original throttle body in, reset IAC and see what she does.

Midnight 85

The tb is smooth through it's full range of travel, no sticking or binding of any kind. Thanks anyway

RRT vette

The IAC might be new, but have you tested the wiring to it.

Also, is the MAF sensor connected good and have you tested the wiring and clean the wires.

It could also be due to a bad connection/wiring at the CTS or the CTS is faulty.

The tune is correct I assume?

I guess there are no stored codes?

Midnight 85

No codes, tune is perfect, (Azzato chip) and all connections are clean and tight. I do believe I may have found the problem, I have pink top injectors in the engine and not only are they apparently leaking but the ohms are not up to 16. They are running from 14.9-15.1. Pressure drops from 42 to 25 in less than 5 minutes. Shoulda known a darn Ford part wouldn't work in a Chevy.

RRT vette

The injector coils look fine to me. Not all injectors ohm 16-17 like has been posted many times. As long as they are all over 10 ohms and ohm close to each other, they are fine. The fuel pressure leak down is not terrible either. Not the best, but that leak could be coming from many places other than injectors. Did you pinch off the fuel feed line after priming the system and watch the fuel pressure guage? Did you do the same for the return line?

Personally, I think you are getting unmetered air the the intake, that the ECM is not accounting for.

Midnight 85

I was doing some checking and I see that the Accels ohm at 14.4 so I see where the pinktops are ohming acceptable. I'm getting ready to do the tests on the feed line and the return line now. As far as umetered air goes, why would the engine eventually idle down to the target idle?

AGENT 86

Do you have datamaster or similar ??

tequilaboy

I would say the tune is not perfect based upon what you have described.

Yo-yo idle after startup indicates problems with start up fueling, open loop fueling and spark advance.

High idle rolling in gear and slow return to PID idle indicates less than ideal IAC tuning, warm park position table doesn't fit the min air setting, overspeed gains to low, delays too long etc.

Midnight 85

I have the Autoxray 2000, but I don't think it's sophisticated enough to find the trouble. If I'm wrong please advise because I am totally lost in that department.

Midnight 85

So you feel the problem may be in the chip? Sorry to be such a dummy but as I stated above, I'm out of my league here.

Midnight 85

I did a scan with the Autoxray 2000 and here's the results, maybe someone can make some sense out of it for me. The EGR has been tuned out of the chip.
Prom ID...................................... ....51905
MAF..................................... .........10 gr/sec.
vehicle speed..................................0
rich lean flag...................................r ich 17
tps..................................... .......... .54
power steering
i high.................................... .........no
Man air temp...................................1 23.8
a/c....................................... .........requested
O2 cross counts...............................0
coolant temp...................................1 69.2 (160 stat)
learn control................................. ...enabled
rpm..................................... ...........925
p/n....................................... .........detected
O2 sensor.................................. .....308 m volts
fan #1...................................... ......off
block learn................................... ...96
IAC motor pos.................................32 steps
inj. pulse................................... .....2.0 ms
EGR duty cycle................................0%
loop status.................................. ...open
integrator.............................. .........128
EGR..................................... ..........off
knock sensor.................................. .141

tequilaboy

Block Learn: 96

Thats pretty low considering the normal BLM min is 108, this must've been reduced in the tune. Nonetheless, a very rich indication.

Midnight 85

I have finally whupped it! Here is what I ended up doing. During all the fuel pump testing I noticed when I powered the pump a couple times it only went up to 20 lbs. Then when I would do it again it might go to 42 or stay at 20. I always carry a spare pump so I changed the old pump out and did away with the pulsator or whatever it's called right above the pump. I believe it was Agent 86 had mentioned he had done that in a previous post I found in the search. All injector tests turned out okay. Then I got to thinking about tequilaboy saying the IAC may have been off. I recently put a new one in and I don't remember where I read it but I read that when changing the IAC the minimum air idle settings didn't need to be redone. That, friends and neighbors is a CROCK! I just did the IAC & tps again and the darn thing is doing everything the way it should be. Now all I have to do is sit back and wait for the next predicament to show itself.
Many thanks to jsup, RRT, Steve40th, coupeguy2001, agent86 & tequilaboy for all your assistance. I only hope I can return the favor someday.