Problem with idle speed

[Lavey29]

Hi guys, I recently added an intercooler to my 540 and bumped the boost from 3 to 7psi. Should be around 850hp now,,used to be 700hp. My idle speed used to sit right at 1100rpm and drop to 850rpm in gear. Motor would never die at idle. After the upgrade, the motor now lopes between 500rpm and 1100rpm and when I shift into gear it dies out often at idle (cold) speed. I had the EFI brain box reprogrammed by the engine manufacturer for the upgrade and everything should be running the same as prior to the upgrade. I have been told there may be a problem with my IAC valve. Where is this part typically located on a motor with Blower shop supercharger and EFI tech throttle bodies? How do I know if this IAC valve is not working right. I replaced the fule regulator and the fuel pressure is 20psi at idle per manufacturer specs. Any help would be greatly appreciated....thanks..
Marc

[79centurion]

IAc should be on the t-body itself. If it isnt working at all you can test by unplugging it. If you unplug it and nothing changes then its probably no good. You can pull it out to see if it moves back and forth with the engine running(if it will without it) just cover the hole.
Dan

[Lavey29]

Thanks alot Dan,,,I will try what you suggest if I can just find this damn thing on here..

[TIMINATOR]

Idle mixture will need to be richer with the intercooler. The air is colder, and there is more internal area to cover with fuel. TIMINATOR

[cfm]

Is it tbi ? If it is and you are running water thru innercooler at idle this could cause fuel puddling and your issues. Most will use transom mount pick up's for carb/tbi or a water psi regulator that will let water go to intercooler at certain psi.

[HeavyHitter]

If the engine used to idle at 1100 out of gear and 850 in, the IAC never worked. Programmed idle speed is maintained +/- 100-150 rpm depending on how well it's tuned. The lope is a product of the intake pressure signal. Bigger the cam the harder it is to maintain a constant signal. Should do better with a load on it so the idle speed should be +/- 25-50 rpm in gear. Both numbers should cycle around the programmed rpm or the IAC is not working/connected. With no IAC less timing at idle will allow the engine to run in or out of ger better.

[Lavey29]

Idle mixture will need to be richer with the intercooler. The air is colder, and there is more internal area to cover with fuel. TIMINATOR
Seems like it is running rich at idle now though. Idle fuel pressure is set to 20psi per Keith Eickerts recommendation. Just seems like it is not getting the correct air/fuel ratio at idle and that is causing the loping. Might have to do with the fuel mapping of the EFI box.

[Lavey29]

Is it tbi ? If it is and you are running water thru innercooler at idle this could cause fuel puddling and your issues. Most will use transom mount pick up's for carb/tbi or a water psi regulator that will let water go to intercooler at certain psi.
It is TBI with offshore pick up for intercooler only. No water in intercooler at idle....thanks

[Lavey29]

If the engine used to idle at 1100 out of gear and 850 in, the IAC never worked. Programmed idle speed is maintained +/- 100-150 rpm depending on how well it's tuned. The lope is a product of the intake pressure signal. Bigger the cam the harder it is to maintain a constant signal. Should do better with a load on it so the idle speed should be +/- 25-50 rpm in gear. Both numbers should cycle around the programmed rpm or the IAC is not working/connected. With no IAC less timing at idle will allow the engine to run in or out of ger better.
Thanks for the info. It definetly idled at 1100 in neutral and 850 in gear. Smooth, nver stalled even when cold start. The cam was not changed. The only thing we did was add intercooler and bump the boost from 3 to 7. I also had the EFI box reprogrammed by the engine builder to match the engine upgrade which is exactly the way he does it at his shop. It does better when the engine is hot but still has the big lope. Eickert says it should basically idle the same as it used to at 1100/850 (gear). Here is a pic of the motor before the adding the intercooler. Where is the IAC plug in on here if you can direct me please. Thanks for the help...

[cfm]

Cool on the intercooler water set-up.
IAC will typ have 4 wires going to it. They will usually be screwed to t-body with 2 screws.
Did we pull the distributor or adjust the timing by chance ? If the initial timing is off this can really make a SC EFI motor idle like poop. Most EFI systems have their own peculiar set of steps you have to do to set the initial timing. If not followed 100% then the timing won't be where you think it is. Must check with Eickert (sp?) on how exactly this is done.

[cfm]

Hard to tell on my monitor but I circled in red what appears to look like an IAC from my standpoint.

[HeavyHitter]

That's the IAC but can't tell if there are wires going to it. Should be 4 wires. Two for fast response and two for fine response. I can see it loping from 700 to 1000 rpm out of gear settling into 800-900 in gear if the IAC is working. The injector timing has been cranked up to handle the extra boost. This will make a difference at ilde as well which will make the lope worse and harder for it to handle a load dropped on it. Either that or they upped the injectors to the next size which will make a huge difference in idle performance.

[Lavey29]

Cool on the intercooler water set-up.
IAC will typ have 4 wires going to it. They will usually be screwed to t-body with 2 screws.
Did we pull the distributor or adjust the timing by chance ? If the initial timing is off this can really make a SC EFI motor idle like poop. Most EFI systems have their own peculiar set of steps you have to do to set the initial timing. If not followed 100% then the timing won't be where you think it is. Must check with Eickert (sp?) on how exactly this is done.
I do not believe any adjustment was done to the timing or the distributor was pulled. But the EFI box was reprogrammed for the upgrade with fuel mapping etc...if the timing was off would you get bad idle but good performance at speed or should you get poor performance at idle and all the way through the power band? thanks for the help..

[Lavey29]

Hard to tell on my monitor but I circled in red what appears to look like an IAC from my standpoint.
thanks CFM,,,that is what I was assuming was the IAC also. There are 4 wired going to it. So I can basically unplug this thing and see if there is any change in the idle. If not, then this IAC is not working right???

[Lavey29]

That's the IAC but can't tell if there are wires going to it. Should be 4 wires. Two for fast response and two for fine response. I can see it loping from 700 to 1000 rpm out of gear settling into 800-900 in gear if the IAC is working. The injector timing has been cranked up to handle the extra boost. This will make a difference at ilde as well which will make the lope worse and harder for it to handle a load dropped on it. Either that or they upped the injectors to the next size which will make a huge difference in idle performance.
Thanks HH,,,that is the part I thought may be the IAC also. No injectors were changed but the EFI box was reprogrammed for the upgrade, fuel mapping, curve etc...Absolute marine checked it a few weeks ago. They found the idle fuel pressure at 10psi but Eickert said it should be 20psi. They changed my Aeromotive regulator which they thought may have gone bad. They set the new one at 20 and did minor adjustment to the idle speed control. It gave a little better idle in gear management after it was warmed up but still died a few times and is no where near what it used to be. I am going to try the suggestion of unplugging the IAC at idle and see if any change happens. I guess that will tell me if that part is working right or not? Thanks again for the advice. I am always amazed at the high level of knowledge people have on this website and how helpfull people are with problems.

[Strip Poker 388]

Why was it Idled so high?Mine is at 850hp and idles at 750-800 and drops when put in gear and the Iac recovers back to the set 750.

[Lavey29]

Why was it Idled so high?Mine is at 850hp and idles at 750-800 and drops when put in gear and the Iac recovers back to the set 750.
When I got the boat that is where the engine builder had it set. Seemed to work fine. Started at the first crank and set right at a smooth 1100 out of gear. Nice motors you got in that pic. I'm certainly no expert, but in reading about motors and blower set ups, seems like the engine builders like those Whipples for a variety of reasons including their idle capability in high HP motors. Roots blowers are a little harder to get a smooth idle in high HP engines. I think I also have a little tweaking to do because I switched from a 4 to 5 blade prop which puts a bit more load on things going into gear at idle speed.

[79centurion]

Unplug it and see what hapens. It should die or idle really low if is working, nothing should happen if its bad.
Dan

[Lavey29]

Thanks dan...hopefully its a simple fix