A friend of mine bought a 2001 Camaro with a 427 stroker we swapped cams for a bigger 248/252. The tune shop has his idle at 950. But we were told that it should be lower and when we asked why it couldn't he said it's because at idle now the car has low vacuum as is. Their is no vacuum leaks btw either. He said it could be the over lap of the cam which I believe is 610/610 lift a 112 lsa. But upon further inspection we noticed whoever had the car before him had about 12-14 inches of rubber hose connecting the map sensor to the back of the intake through a small port not the map port its a fast 102 btw. So my question is could this be giving the tuner a false reading and making it seem like there is not much vacuum when their is. And by removing the hose and mounting the map to the front of the intake effectively changing the reading allowing him to lower the idle. Or won't it matter?

 

My 01 has a 427 with a 243/251 cam on a 115+4 LSA. It idles around 900-950 rpm and was tuned by one of the best so there's some truth to what the tune shop is saying. I have the map sensor installed on the front of my FAST and I'm getting 12-14" of vacuum which is enough to work the power brakes but it don't stop as good as I'd like.

 

ok cool we just didn't know if the map should be hooked directly to the intake or if it's ok to have it attached to the rubber hose. But what about my car? Mines a 408 with a 244/248 612/612 112 lsa cam and idles around 950 shouldn't mine be much lower then?

 

I'd put it on the intake manifold if it was me. I'm curios as to why they installed it on a hose in the first place.

 

I looked at mine and mines attached to a rubber hose too about 6 inches though and we are idling around the same but his is a much bigger cam. I didn't install the hose on mine though I think the tune shop prior to this one must have. Do the hoses hurt vacuum or doesn't it matter? I'm installing mine on the front but I really don't want to pay for a retune if if will change things...

 

I'm not one to answer that but my guess is that it will not affect the tune dramatically and you may gain a slight amount of vacuum.

 

You might want to try and post this in the Diagnostics and Tuning section.

 

I’ve seen quite a few guys run their MAP out on a rubber tube. It doesn’t affect anything as long as the tube isn’t collapsing. I almost did mine that way. My MAP didn’t fit my MSD ports, and no one knew what MAP to get at the time, so I ended up machining my MAP port on my MSD and modding my MAP sensor to get it to fit correctly.

 

Nothing wrong with the rubber hose unless it gets filled with oil from effed up PCV.

The reason for doing that is usually accessibility. It sucks trying to service the map the way it is factory mounted. On mine I extend the harness and attach it up front. Maybe less clean but easier to work on.

 

how? you have a smaller cam on a wider lobe separation. Its going to pull more vacuum than his.

OP, What is "low vacuum"? You never listed what the vacuum is. and 950 rpm is about right for that size cam. I'm not sure what the problem is.

 

if things arent adjusted correctly, you will give up a few inches of vacuum. If the tuner relied more on throttle blade opening (air) than he did on adding some timing and getting the afr set to pull the most amount of vaccum, then you will give up idle quality and potential vacuum. there a fine balance to getting it just right. This is what separates a good tuner from a meh tuner.

 

Not sure I'm following that. Maybe I misread something. On a gen 3 controller (with IAC solenoid), you DO need to control idle by opening the blade to get the warm idle counts down into the 30-60 range or else you'll be commanding the thing open almost all the time and be guaranteed a hunting, uncontrollable idle.

On larger cams, I have found that you need to do the following to get it stable:

1. Idle lean. In reality, it isn't idling lean, but with so much overlap, it will read false lean at idle and keep trimming rich. Often requires open loop or hybrid tune to get it to stay lean at warm idle.
2. open the blade until you get to 0.67 volts on the tps (VOLTS not percent). If you sill have high IAC counts at warm idle, you need to drill a hole or make the existing hole bigger to get the counts down
3. Set your idle timing relatively low. A lot of the older tuning guides said to run your idle timing up and latch it to your main tables etc. No. Drop your idle spark timing to around 18 degrees in the 800 and 1200 columns in both P/N and Gear tables. Set 0 and 400 columns to 33 degrees, which is usually your highest torque spark for idle speed on the LS.
4. Make your adaptive spark aggressive enough so that at 200 RPM error, you are at 32 degrees timing. if you use 18 as your base, then you should be 14 advanced at 200 RPM error. Use 12 at 100 error and interpolate down to zero. Make your overspeed tables match, but using negative numbers.
5. Don't worry about making your main tables and idle tables match. Set your switchover point to 1.2% throttle and 400 kph. Below 1.2% you'll be in the idle tables at all speeds.

There's more, but it isn't relative to this thread. Doing those steps, you will sacrifice a very minor amount of vacuum at idle, but you will be much closer to stability. Often, you have to adjust your PID for idle air rather dramatically to get the idle under control with very large cams.

one thing increasing idle speed does is also increases idle vacuum. So if you are concerned abour vacuum, nothing wrong with bumping the idle speed. FWIW, my 427 idled at 850 when it had the 248/255 cam in it. With my new cam, I'm guessing 950 will be the minimum.

 

Thanks all for the reply but we are having this issue now where when he comes to a stop the car wants to hang around 1400 rpm then drop to its idle around 2 to 3 mph but in doing do it stalled 3 times. The tuner has been tuning cars for alooong time but it's kinda pissing him off after 600 dollars and he has to baby it home so it won't stall is ridiculous we can't figure out why it would do that and the tuner said something about pulling 10lbs of vacuum at park idle and in gear idle so he fixed that but it still stall going in reverse and on sudden stops. Kinda think something is up... And I seen cars with huge cams idle lower then his and drive better to so wth

 

Got a tune file and a log?