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Joe I feel your pain. I have an IAC at 0 as well, but as I said in my previous post, the idle is spot on according to my FSM. Just like you, I've looked for every damn vacuum leak and none. I wonder how many other people have an IAC at 0, but won't know because they don't datalog. Not sure if I missed it, but are TPS voltage and percentages correct? Specifically look at that when at idle.
I did. I put a vac cap on the fitting to the U shaped hose for the PCV.
This thing has me stumped.
The only thing I didn't isolate is the FPR, which I might check tonight.
-- Joe
So you capped off every nipple and it still does that? Why don't you try running the car WITHOUT the MAF? That will force it into open loop and see what happens. If it still does that, maybe cover up the IAC hole and see what it does?
So you capped off every nipple and it still does that? Why don't you try running the car WITHOUT the MAF? That will force it into open loop and see what happens. If it still does that, maybe cover up the IAC hole and see what it does?
Tried that too. Idles at 3,000 RPM!
When the maf is unplugged, it sets a code, and the iac actually opens.
Same thing when the TPS is unplugged.
I'm trying to figure out a way to cover the iac hole with something that won't get sucked in..
The only thing I didn't cap off was the FPR, which I'm gonna go do right now.
When the maf is unplugged, it sets a code, and the iac actually opens.
Same thing when the TPS is unplugged.
I'm trying to figure out a way to cover the iac hole with something that won't get sucked in..
The only thing I didn't cap off was the FPR, which I'm gonna go do right now.
-- Joe
What is wrong with your thumb or finger? I did. I only lost 2 fingers. What I am thinking of is running the car with the MAF off and the IAC covered. You need the hose off. If it dies, I would wonder if the MAF is bad. It seems like it is working if you remove the MAF so maybe the MAF is bad? This one I can't help you. I don't have a MAF even if I lived nearby.
OTOH, I don't have any experience with your car year but looking at the scan, is it normal for the O2 on the left to be so low while the right is so high (relatively)?
PS. Your handle sounds familiar. Were you on 3rd Gen?
From what I know or think I know....
when the engine is warm you need to disconnect the iac and manualy set the idle to around 450/ 500 rpm, so when you connect the iac it will adjust your idle upto the desired speed.
as you iac counter is at zero there is no adjustment left to lower the rpm.
once rpm is set then you need to check your tps sensor to ensure you have .54 volts at idle... if this doesn't sort it then I'd be checking the timing etc...
but the main thing is set base idle lower then needed then let the iac adjust it upwards...
hope this helps
From what I know or think I know....
when the engine is warm you need to disconnect the iac and manualy set the idle to around 450/ 500 rpm, so when you connect the iac it will adjust your idle upto the desired speed.
as you iac counter is at zero there is no adjustment left to lower the rpm. once rpm is set then you need to check your tps sensor to ensure you have .54 volts at idle... if this doesn't sort it then I'd be checking the timing etc...
but the main thing is set base idle lower then needed then let the iac adjust it upwards...
hope this helps
If you are insistent on going that way you need to zero out the IAC and make sure that the timing is spot on and that your tach is right. IDK why the F-body tachs were good and the Y-body tachs don't seem accurate.
I'd check timing first. You are right that 0 counts means that no adjustment is possible. As to setting the TPS, depending on whether you have the later L98 or not, you may or may not be able to set it. Mine is a 91 and the TPS has 2 screw holes and NO *****. So it takes the startup voltage (within reason) as the base.
Ah, but the question is how much lower to set it. ASSUME that you have a stock system, ASSUME that you have timing set, ASSUME that the tach is accurate and ASSUME there are no air leaks isn't my idea of setting. More like guessing which is why I don't like this method.
What is wrong with your thumb or finger? I did. I only lost 2 fingers. What I am thinking of is running the car with the MAF off and the IAC covered. You need the hose off. If it dies, I would wonder if the MAF is bad. It seems like it is working if you remove the MAF so maybe the MAF is bad? This one I can't help you. I don't have a MAF even if I lived nearby.
OTOH, I don't have any experience with your car year but looking at the scan, is it normal for the O2 on the left to be so low while the right is so high (relatively)?
PS. Your handle sounds familiar. Were you on 3rd Gen?
I'm a moderator and one of the original members from thirdgen.org
I can't put my finger over it because if I remove the MAF from the air intake stumbles and idles all over the place.
I did put some duct tape over it, and it started and stalled immediately.. Which tells me that the air is in fact going through the IAC passage. So tomorrow the TB is coming off again for inspection. wtf.
The o2 swings up and down, and appears to be normal. Even still, I can force open loop in the tune and rule out any o2 based corrections.
I would have continued playing with it, but the starter died.. I swear to god the car is cursed.
I'm a moderator and one of the original members from thirdgen.org
I can't put my finger over it because if I remove the MAF from the air intake stumbles and idles all over the place.
I did put some duct tape over it, and it started and stalled immediately.. Which tells me that the air is in fact going through the IAC passage. So tomorrow the TB is coming off again for inspection. wtf.
The o2 swings up and down, and appears to be normal. Even still, I can force open loop in the tune and rule out any o2 based corrections.
I would have continued playing with it, but the starter died.. I swear to god the car is cursed.
So I went out and got drunk instead.
-- Joe
Spent many an hour there.
I obviously haven't done this before but people have suggested that the MAF unplugged will force it to disregard values and go back to original program. So when you did that, could you get the engine running and keep it running by disconnecting the MAF? Supposedly you can test the MAF that way.
From what I know or think I know....
when the engine is warm you need to disconnect the iac and manualy set the idle to around 450/ 500 rpm, so when you connect the iac it will adjust your idle upto the desired speed.
as you iac counter is at zero there is no adjustment left to lower the rpm.
once rpm is set then you need to check your tps sensor to ensure you have .54 volts at idle... if this doesn't sort it then I'd be checking the timing etc...
but the main thing is set base idle lower then needed then let the iac adjust it upwards...
hope this helps
That's actually not how the code works in $EE. On startup, the IAC fully retracts. The amperage on the coil driver spikes indicating the IAC is fully retracted. That is the 255 position. The ECU then extends the IAC to the target crank steps (usually around 45).
I obviously haven't done this before but people have suggested that the MAF unplugged will force it to disregard values and go back to original program. So when you did that, could you get the engine running and keep it running by disconnecting the MAF? Supposedly you can test the MAF that way.
It idled at 3,000 RPM with the MAF disconnected.
I've never tinkered with a hybrid MAP/MAF car. $EE is a weird calibration. I'm actually tempted to delete the MAF in the carlibration and go MAP only, but I don't wanna mess with the tune until I resolve this idle issue. It's an otherwise stock engine, so I don't want to run a non-stock calibration.
The only thing I changed in the tune was the cooling fan turn on temperatures.
So, I have some aftermarket (holley, BBK) throttle bodies in the shop and I noticed one major difference. In addition to the IAC passage, there is a small hole about 1/8" drilled that provides free air even if the IAC is fully extended (closed).
On the aftermarket throttle bodies, this hole does not exist. I'm not going to run one of these throttle bodies on my LT1, however I'm thinking of putting a #10 screw with some loctite in that hole. I tapped it this AM, and am gonna run out to the store and get some screws.
Maybe this hole is just allowing too much air ? It' on both factory throttle bodies, but again when I googled this problem several people complained about the exact same situation and no resolution in any of the threads.
So, I have some aftermarket (holley, BBK) throttle bodies in the shop and I noticed one major difference. In addition to the IAC passage, there is a small hole about 1/8" drilled that provides free air even if the IAC is fully extended (closed).
On the aftermarket throttle bodies, this hole does not exist. I'm not going to run one of these throttle bodies on my LT1, however I'm thinking of putting a #10 screw with some loctite in that hole. I tapped it this AM, and am gonna run out to the store and get some screws.
Maybe this hole is just allowing too much air ? It' on both factory throttle bodies, but again when I googled this problem several people complained about the exact same situation and no resolution in any of the threads.
Starter is all set.
Rear main seal leaks oil though. wtf.
-- Joe
That picture of the factory throttle body seems to be open quite a bit, is that the one your were running and is that all the farther it closes?
That picture of the factory throttle body seems to be open quite a bit, is that the one your were running and is that all the farther it closes?
It's completely closed. What you are seeing is the paste the factory puts on the blades and the bore.
This experiment was interesting. For about 30 minutes it solved the problem. Was idling around 600 at 160 steps.
Then I shut it off, restarted and it was idling at 1100 at 0 steps.
I'm starting to think the IAC wiring is intermitant. I'm going to ohm it out tomorrow. I think maybe the IAC only moves sometimes.
The other thing that is baffling to me is the TPS percent sometimes reports higher than 0 at idle. I've verified that the throttle is hard against the screw. It will read 3.8%, i'll blip the throttle several times and it will read 0 again. Maybe the TPS is faulty as well.
Had a code 16 again, which is odd since I replaced the opti and opti harness last week. I'm starting to think the LT1 is an unreliable setup haha.
Edit: I forgot to add, with EEHACK I can hard set the IAC steps from 0-160 for troubleshooting. It didn't do a thing to the idle.
I might go out in a second and test it with another valve I have just to see if the pintle moves back and forth.
The other thing that is baffling to me is the TPS percent sometimes reports higher than 0 at idle. I've verified that the throttle is hard against the screw. It will read 3.8%, i'll blip the throttle several times and it will read 0 again. Maybe the TPS is faulty as well.
-- Joe
Is it possible that the throttle shaft is binding with engine vacuum and not returning to the idle fully closed position? I have seen this happen in the past, one way to check is when the car is idling high go out and see if you can close the throttle blades farther against the stop. It sure seems like this is your problem, with the high idle and different TPS readings.
Is it possible that the throttle shaft is binding with engine vacuum and not returning to the idle fully closed position? I have seen this happen in the past, one way to check is when the car is idling high go out and see if you can close the throttle blades farther against the stop. It sure seems like this is your problem, with the high idle and different TPS readings.
I've seen that too with weak throttle springs. I checked it, forcing the blades closed.
The TPS could be a bad ground. The way the PCM is wired, the TPS has a separate ground. I noticed the grounds have been tampered with when I pulled the harness apart just now. I'm gonna fix those.
So I connected a IAC stepper and commanded the IAC to move around. I got it to retract once (open) but then it stopped moving. I suspect a wiring issue between the C connector (gray/clear) and the IAC plug.
I can't tinker with it any more today, but I'll ohm out the harness tomorrow, fix any grounds. If I find a broken wire for the IAC we know that's the problem. If not, it's probably a faulty PCM.
I've seen that too with weak throttle springs. I checked it, forcing the blades closed.
The TPS could be a bad ground. The way the PCM is wired, the TPS has a separate ground. I noticed the grounds have been tampered with when I pulled the harness apart just now. I'm gonna fix those.
So I connected a IAC stepper and commanded the IAC to move around. I got it to retract once (open) but then it stopped moving. I suspect a wiring issue between the C connector (gray/clear) and the IAC plug.
I can't tinker with it any more today, but I'll ohm out the harness tomorrow, fix any grounds. If I find a broken wire for the IAC we know that's the problem. If not, it's probably a faulty PCM.
But either way, I think we're narrowing it down.
-- Joe
what you need to do is connect an iac noid light to the iac connector and see whether it gets command when you apply and remove loads...
other way is to remove the iac valve, plug the hole and start the car...by increasing and decreasing loads your be able to see if the Pintle moves in n out
What I am thinking of is running the car with the MAF off and the IAC covered. You need the hose off. If it dies, I would wonder if the MAF is bad. It seems like it is working if you remove the MAF so maybe the MAF is bad? This one I can't help you. I don't have a MAF even if I lived nearby.
