Holley Sniper Question?

[ggunter]

I have the Holley Sniper on my 347 and for the most part I really like it. But occasionally get this annoying rev up of the engine( usually when the engine is being loaded down like pulling away from a stop light)from the IAC and most times it will drop back down after 3-5 seconds. Yesterday as I was pulling back into the garage it started doing it and I let it go to see how long it would go on. After 30 seconds I became annoyed, and loaded down the engine with the clutch and it settled down. My throttle position sensor is at 1 and the IAC is around 7. I had heard there can be an issue with the intake manifold center divider can cause this but mine is cut down 1/2". Anyone have any thoughts?

[Norm B]

Do you have room to put a 1/2 inch open spacer under the Sniper? Even with the centre opened up on the manifold it is possible for the map sensor port to be blocked.

Norm

[FF33rod]

I have the Holley Sniper on my 347 and for the most part I really like it. But occasionally get this annoying rev up of the engine( usually when the engine is being loaded down like pulling away from a stop light)from the IAC and most times it will drop back down after 3-5 seconds. Yesterday as I was pulling back into the garage it started doing it and I let it go to see how long it would go on. After 30 seconds I became annoyed, and loaded down the engine with the clutch and it settled down. My throttle position sensor is at 1 and the IAC is around 7. I had heard there can be an issue with the intake manifold center divider can cause this but mine is cut down 1/2". Anyone have any thoughts?

Yup, I have the same issue from time to time on my 347, very rare but it happens. Haven't tried to figure it out yet (so no googline). Which manifold do you have? I have a non modified Edelbrock RPM air gap (dual plane). The center divider has a notch built in. Hood clearance would be an issue with any spacer :(

[Papa]

I had an issue where the car would high-idle when coming to a stop. The solution was adding a wrap on the throttle linkage spring. Another common issue is that the butterflies can shift on the shaft and rub the venturi causing them not to close properly. If the issue is the latter, you can simply adjust the parts to get them properly aligned. There are some good posts on the Holley Sniper Forum for both. When I did the spring wrap, I found a great video on YouTube that showed how to add the wrap with a zip tie.

Another potential issue is that the built-in fuel pressure regulator is failing. Do you have a pressure gauge on the inlet that you can verify 58 psi with? Mine failed and I was pushing 100+ psi into the TB.

[hineas]

I had an issue where the car would high-idle when coming to a stop. The solution was adding a wrap on the throttle linkage spring. Another common issue is that the butterflies can shift on the shaft and rub the venturi causing them not to close properly. If the issue is the latter, you can simply adjust the parts to get them properly aligned. There are some good posts on the Holley Sniper Forum for both. When I did the spring wrap, I found a great video on YouTube that showed how to add the wrap with a zip tie.

Another potential issue is that the built-in fuel pressure regulator is failing. Do you have a pressure gauge on the inlet that you can verify 58 psi with? Mine failed and I was pushing 100+ psi into the TB.

This!

I was having a similar issue where sometimes I would get an odd surge, almost like the throttle was sticking. My engine would also sometimes idle at 1500-3000 rpm but my throttle position was 0 and my IAC was 7.

Finally after several weeks of trying to figure out what was going on it happened while pulling into the driveway. I popped the hood and I could see that the secondary throttle linkage was sticking partly open when the primary was completely closed. I tapped it with my finger and it closed and the engine went back to my normal idle.

On my research I have seen 2 main fixes. The first was an extra wrap of the spring to help the blades close. Here is the video on how to do it.

https://youtu.be/avRqQZBOxP0

I did the extra wrap on the spring and it is almost completely fixed. I have been driving it for about 300 miles since then and it only had the issue one morning when it was cold. This DOES stiffen the pedal though.

Another fix I have seen online is to readjust the throttle blades. Sometimes these aren't perfectly centered in the throttle body and stick partly open. Some people say it is due to uneven torque on the throttle body causing it to stick. Either way, if the blades are sticking you can re- center them so they don't stick. To do this you have to remove the throttle body because the adjustment screws are on the underside of the blades. There are several threads on this if you search the Holley forum for sticking secondaries.

[BradCraig]

Ditto on the extra spring wrap on secondaries.

[ggunter]

I'm pretty positive my throttle blades are not sticking as I get that huge sucking sound when this occurs telling me it's the IAC thinking the engine is going to stall, so I assume it is trying to prevent that by raising the idle. I get that happening more when the engine is cold and I'm backing out of the garage, but it usually settles down in 3-4 seconds. This usually will not happen when the engine is hot. The car was hot the other day when this happened and I let it go on to see how long it was going to do this and I blipped the throttle a couple times to try to knock it down and I just got tired of it after 30 seconds. I do have a gauge right at the inlet to the throttle body and it is reading 58 psi. I will double check the throttle blades just to make sure, but I restarted it the other day without touching the throttle and it started and idled normally. If it is the IAC going bad I wonder if they are replaceable from Holley?

[Papa]

It may be worth doing some data logging to see exactly what's going on when it happens.

[bingo2]

Standard Motor Products AC416 IAC Motor. Should be available at most parts stores.

[ggunter]

Looking around online I ran across "EFI System Pro" that had a ton of info on the Holley Sniper and issues one might run across. I downloaded a bunch of material and will sift through it this weekend. Thanks for all the replies, I'll let you know what I find out.

[bobl]

To idle fast it must be getting extra air or the timing is advancing. You can check timing on the hand held (if sniper controlling timing) to see if that is what is causing it. Extra air can only come from the throttle blades, IAC or a vacuum leak. Prove which one before making changes. You can run it without the air filter. When the idle hangs place your finger over the idle air port on top of the throttle body to prove if the iac is causing it. If not the IAC, Then try pushing the throttle blades closed to see if that is where it's getting air. If it's the IAC hanging it can be fixed in software. If it's not shutting off the air when commanded then it's defective (not too likely). You might try plugging off the pcv valve to make sure that's not causing any issues. If Sniper is not controlling timing it could be the advance mechanism (vacuum or mechanical) hanging.

Bob

[Avalanche325]

One other thing timing related that has happened on my carbed car. It felt like the throttle was sticking. To support that, a quick throttle blip would often bring it back down. After playing with return springs, checking throttle plates, etc. I found that it was the mechanical advance that was sticking. I opened the distributer and took the "football" apart, cleaned it.......problem solved.