Idle drop while braking,backing out of driveway

[1994rcsbLS]

My thoughts exactly especially after he says it went to 3000 revs.
Pinch the hose or pull it and plug it.

This was done at idle, booster disconnected, gauge to booster line. Let idle, then checked at 3k rpm to see. My helper is vehicle illiterate so it’s been a rough day lmfao

I even smoke tested and found zero smoke pushing out anywhere.

Engine also assembled by a great reputable shop in Nc.

Not sure about this tho. I held brakes and revved engine up. Obviously brake on -idle drop. Revved back up to normal. Peddle felt fine.
Under neutral revved it up And pedal pressed. At like 3k rpm. Pedal sank a little further down. Assuming bc vacuum was built and assisted pedal a bit.

At this point I’m looking at a pump to assist with added vac. Thoughts

 

[1994rcsbLS]

Is that in Park/Neutral? Probably 6" or less in Drive and even less in Reverse. With GM transmissions, Reverse is the toughest gear to make a fairly rowdy combination idle. The line pressure increases adding load to the pump.

That’s park. I didn’t try neutral. Not sure why. But easy enough I can do that later on.

 

[Scooterwrench]

Like MaxEx said you can change idle with timing too. Is there a table in the terminator program for idle vs rpm timing? With our factory PCM's there are tables to adjust for drops and flares like putting it in and taking it out of gear,A/C engage and disengage, drops and flares from brake booster etc. Small changes are mostly contolled by timing like the A/C and brake booster. large changes will be controlled by both timing and IAC. When you drop it in gear timing will advance first because it can react quicker and save the engine from stalling until the IAC can step up. Opposite when you go to park or neutral. Timing falls first to keep it from flaring while the IAC is stepping down. It's kind of a balancing act to get the two to work together but once you get it dialed it your transitions will as smooth as if it had a governor on it.

 

[1994rcsbLS]

Like MaxEx said you can change idle with timing too. Is there a table in the terminator program for idle vs rpm timing? With our factory PCM's there are tables to adjust for drops and flares like putting it in and taking it out of gear,A/C engage and disengage, drops and flares from brake booster etc. Small changes are mostly contolled by timing like the A/C and brake booster. large changes will be controlled by both timing and IAC. When you drop it in gear timing will advance first because it can react quicker and save the engine from stalling until the IAC can step up. Opposite when you go to park or neutral. Timing falls first to keep it from flaring while the IAC is stepping down. It's kind of a balancing act to get the two to work together but once you get it dialed it your transitions will as smooth as if it had a governor on it.

I’ll have to check again. I know there is. I just didn’t wanna mess with tune since it was Done and dynoed. I’ll get into the system and check it out Tomorrow.

 

[L31MaxExpress]

I’ll have to check again. I know there is. I just didn’t wanna mess with tune since it was Done and dynoed. I’ll get into the system and check it out Tomorrow.

Idle timing will not mess with the area of the spark and fuel maps that are dyno tuned. I do not know of any dyno tuned setups running right without some street, drivability tuning included as part of it.

 

[1994rcsbLS]

Idle timing will not mess with the area of the spark and fuel maps that are dyno tuned. I do not know of any dyno tuned setups running right without some street, drivability tuning included as part of it.

Fair enough. So. Based on this:

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Where here would or SHOULD the change be made. ( this is only photo I have atm more will fall tomorrow )

 

[Scooterwrench]

Not sure what P term and D term means. Maybe MaxEx knows.

 

[L31MaxExpress]

First I would look at where your idle timing is set at. I would expect the base value to be somewhere between 14 and 18 with a LS. I usually start about 16. Then with the engine running looke at the timing at idle. I would expect it to vary 4-8 from that 16 setting. Meaning it should look something like this. 16, 22, 14, 20, 16, 14, 18, 22, 20, 16, etc, etc. Then when you put it in Gear, I would expect it to spike to say 24* and when you put it into Park I would expect it to drop to say 8*. If it is not doing something like that, the P & D values need to be tinkered with. IIRC correctly Higher numbers is more variation, but I do not have the Holley tuning manual in front of me.

 

[L31MaxExpress]

Not sure what P term and D term means. Maybe MaxEx knows.

I know P term and D term adjust how much the spark advance reacts to idle rpm changes, but I do not know what each one does. I would have to read up in the Holley tuning manual for that ECU. I have only messed with a couple of Holley systems over the years.

 

[1994rcsbLS]

First I would look at where your idle timing is set at. I would expect the base value to be somewhere between 14 and 18 with a LS. I usually start about 16. Then with the engine running looke at the timing at idle. I would expect it to vary 4-8 from that 16 setting. Meaning it should look something like this. 16, 22, 14, 20, 16, 14, 18, 22, 20, 16, etc, etc. Then when you put it in Gear, I would expect it to spike to say 24* and when you put it into Park I would expect it to drop to say 8*. If it is not doing something like that, the P & D values need to be tinkered with. IIRC correctly Higher numbers is more variation, but I do not have the Holley tuning manual in front of me.

Gotcha ! Ok tomorrow I’ll plug in and take pics of what I have it at So you can see