rvgriff

Have an odd idle issue I could use some help with. Here is the story:
Motor is a 383 TPI and I was well on the way to breaking the beast in when I noticed a vacuum leak on a short drive. I had noticed it before but was unsure if it was just the intake making the noise as I had never heard this motor run before. I was able to identify it as a true leak since it continued to get louder over time. Took her home and let it cool off a bit. Upon inspection I found 2 bolts had loosened up on the runners. One on the passenger side was just a little loose and the one on the driver side was pretty bad and the source of the intake leak. As I tightened it back down to spec It died of course but started back up pretty easily. Took it for a short trip to check it out and about 5 miles from the house as I approached a light it died. Started back up just fine but did not want to idle very well. Every time I reached a light I would have to keep in the gas to keep it from dying. Once I got it back home I was able to come to a stop without hitting the gas just to see what it would do and not have to worry about blocking traffic. When I come to a stop it will almost die as it oscillates and finally normalizes the idle @ 600RPMs at programmed. Here is the odd part….I can start it up just fine and it will idle until the vehicle moves. I can put it in “R” and back up ~10’ and it will start to die and slowly stabilize the idle. Back in “D” and will do the same thing. The really odd part is I can put the vehicle in “N” and let the car roll down the drive and it will do the same thing in ~10’. It is almost like the VSS is sending an odd signal that causes the AFR to freak out as I will notice a spike in the AFR to 15.8 from a steady 14.7. The vacuum leak may have nothing to do with the issue but it seems to be related just simply due to the timing of the issue.
After resolving the intake leak I modified the VE tables a bit to remove some fuel as it was rich after removing the “extra air”. Runs great past 700RPMs. I do see a spike in the AFR but I am not sure what a 1.1 increase means in extra fuel terms. I have searched the forum a great deal and have looked into most of the issues identified in the threads but none have resolved my issue. I will be researching tonight what calculations go into an AFR reading to better educate myself. I am still learning obviously but think I may still be teachable ;-) Guess I still need to prove that to be true so flame on if appropriate and thanks in advance for any ideas of feedback.

Things I have checked:
Plugs were fuel fouled but are running fine now
Wires are bard new and solid
AIC calibrated
VSS voltage set
Base timing with ECU disabled verified
Altenator is keeping the system at a steady 13.8
ALDL shows a proper vehicle speed from the VSS in TunerPro RT

Still need to do:
Get a vac gauge. Now I am going by map as a point of reference
Research AFR to see just what a 1.1 change in AFR really means

livinforhim

did it sit for a long time with no power to the ECM? it screws with the programing(i've been told), My does the exact same thing that your describing, but its a 3.1 liter. I have check everything up and down and then double checked it. I replaced the IAC valve, I'll install it where it suppose to be but for some reason it always creeps backward causing my Idle to soar in RPMs. so my sollution was to but the old broken one back in set it where it idle as close to corect as i can get it, and then i modifyed my throttle body so it would stay slightly open all the time. it gives me a stable idle speed, a little higher than desired, but untill I can find some one to reprogram my IAC settings, thats how it will stay. it does the trick and no more poping in into netrual while im slowing down and gasing while brakeing, cuz that get old fast.

rvgriff

Appreciate the reply. This build is only a few months old and I did reset the ECU as part of the troubleshooting process. It sat with no power for ~15 min just to reset the ECU.

I have purchased an APU1 from Moates but not sure how to interpret/modify the IAC settings. Anyone have any input there? I'll do some research on the IAC settings tomorrow.

Thanks again for the reply!

ploegi

Did you reset minimum idle? (disable IAC, set idle with the screw?)

rvgriff

Yes:

Disable ECU controll of timing. Set base timing. Jumper A-B on aldl. Let sit for a min or two with voltage applied to allow the pentle to fully extend in the IAC. Disconnect IAC. Set idle set screw to desired min idle. Reconnect IAC. Set TPS voltage

fltche1

I am having the same problem with my 86 trans am. it is a 305 with the TPI. I reset the IAC by following the procceedures listed in the service manual... which state put the ignition in the on position and let it run for about a minute to two minutes then disconnect the IAC connector and let it sit in the on position like that for 15 seconds and then start the car and set your idle with the set screw on the throttle plate. I have also replaced my vacum hosing to make sure there are no leaks. I even plugged them to test that there were no leaks. it ran a heck of a lot better than before and smoothed out but it will still osscillate and then drop the rpms and die. I have ran through the MAF system and that is all checking out ok and the mass air flow sensor has been replaced as well along with the mass air flow relay. I am getting a code 33 as well. the manual says its the MAF or a rough idle. well i have completley tested the MAF system with a 12V tester and a digital voltmeter... everything in the MAF checks out within spec and is working fine. But i can't get the TA to idle right and stay running. as long as you are moving and you don't sit at a light or a stop sign for more than 5 to 10 seconds it will stay running... whats going on? im running out of ideas... Thanks BTW... something i forgot to mention is that it only sometimes dies... sometimes you can be sitting there for a minute and it won't die but that is only during the first initial start up when it is cold...