MNR

I installed my VR almost a month ago. I noticed high idle and high crawl speed when cold, upwards of 13-14mph. It only does it when cold but now I noticed the idle fluctuating when coasting, mainly downhill . I really dont like the fact I am basically holding the car back with the brakes when its cold because its definatley noticeable. I want to get rid of this...is it [mail order] tune time?

On the positive side, the VR rocks

bikgc

I'd like to know as well

Svelte_C5

jellis

if you do get a tune, i would suggest a reputable local tuner to do the work rather than a hand held.

Rob04C5LM

You shouldn't need a tune at this point. If you're getting error codes indicating a lean condition, then you need it. My understanding is that the C5 has a lot of room before that happens.

On the other hand, if you're just looking for the excuse, the tune on top of your vararam certainly won't hurt

corvettepete

Was wondering about that too, though my CAI is a Callaway Honker.

MNR

No lean codes, no high idle codes - nothing. That really surprises me. Also, when I was coasting down the interchange ramp to another interstate, it started bucking a little bit. Nothing extreme, but you could feel it.

If I do get a tune I would either get a mail order from ECS or possibly a dyno tune, I'm not really decided yet.

MCVetteLs6

you know .. now that you mention it, i have realized my car as done this as well. i have never paid attention to the weather when this is happening tho, no codes here either..
but like rob04c5lm said.. guess this will just give me an excuse to go get one

jacks996

You don't need a tune with the vararam but you can squeeze a few more HP out if you get one

ChargedGN

Mine does the same with the Vararam, I drive mine everyday on the hi way and when letting off the gas and coasting down a hill it tends to buck lightly.

I assume more air getting in there and the computer may be over compensating with too much gas? or going a little lean?

When I add headers and a exaust I will get it tuned but for now it doesn't bother me that much.

MNR

That's what I am worried about. I don't want to be running on a lean engine...

Bash

What mods do you have?

rebelheart

You should not need a tune.Did you do the proper drive loop?

MNR

B&B Route 66 Catback as far as performance mods.

I did the "let idle for a few minutes" and then the "drive for 60 miles at above 45mph." Except, I have put about 4x that amount of miles on since the intake, with no change in the idle or whatever.

Robert 2000

You don't need a tune I ran my car for over a year with vararam and Corsa catback without a tune. However, I wont argue with picking up a little extra power with a tune.

Rob

SoDiezl350

I'm going to disagree with most of the people here and say I would highly recommend getting a tune, and not just a dyno tune but a street tune.

I had the same symptoms as you and after taking logs with a predator, I found the Vararam leaned out the AFR too much for my tastes. I'm not sure how much leaner the predator made it versus the stock tune but the LTFTs were at around 15%.

Adjusting the injector slope on the predator did bring it closer to nominal but without the ability make adjustments at specific RPMs, it really wasn't enough.

I ended up getting an email tune for the predator from 06MonteSS(he's on this forum as well) who seems to have a very large following on some of the other GM platforms and for $125 the car now runs fantastic. My AFR at WOT is right around 12.5 and my LTFTs are around 3%.

robert miller

I had one on for almost one year did the same check your plugs if you think running rich or lean. With all these so called yes I am a tuner get some info on the tuner befor taking your car. Can do more bad than good. For no more than you have done to the car look at the mail order from ECS just my 2 cents.... Robert

MNR

Exactly what I was thinking. Maybe next week

SoDiezl350

(This is going to be a long attempt at clarifying some of the issues which seem to come up when dealing with intakes, fuel ratios, and tuning. If anyone spots anything wrong feel free to chime in and correct me.)

While I think reading plugs can closely approximate AFR, the actual method required to get accurate readings requires a magnifying glass, a specific type of flashlight, and knowledge of where to look on the plug itself. In addition, the Vararam is only going to cause a lean condition at WOT(wide open throttle), and thus the plugs will be even less accurate in conveying the actual fuel ratio.

The reason the Vararam is only going to cause a lean condition at WOT is because at part throttle the computer is running in closed loop mode. Assuming the O2 sensors are functioning properly, the correct AFR will be generally maintained by the ECU adjusting injector pulse width to maintain a stoich ratio. When my LTFTs are registering at 15%, what it means is the ecu is adding 15% more fuel to hit its target AFR, which it reads from the O2 voltage.

At Wide open throttle, the ECU switches to open loop mode, in which it relies primarily on MAF readings for fuel delivery. Ironically, the ECU switches to open loop mode for fail safe purposes, due to the risk of a faulty O2 sensor giving inaccurate readings(they aren't very accurate to begin with). The MAF on the other hand is very accurate and remains so over a wide range of conditions(assuming internal parameters stay constant).

One common misconception I see spread around(not just here) very often is the idea that the reason a cold air intake will lean out the fuel ratio is because it "increases the ammount of air that enters the engine". This is wrong on several levels.

The first reason that this is wrong is because the ammount of air that enters the engine is primarly dependant on the engine itself. The stock intake is flowing a lot more air at WOT than the Vararam is at part throttle. And yet, the ECU has to adjust the fuel trim at part throttle because the Vararam is leaning out the system.

The second reason that this is wrong is that even at WOT, the flow rate with a Vararam installed is not enough to "peg" the MAF. Pegging the MAF basically means you have exceeded it's maximum flow rate. People are able to run superchargers on the stock MAF, so there is no chance that the Vararam is outflowing the MAF. More info on our MAF here: http://en.wikipedia.org/wiki/Mass_fl...wire.22_sensor

The real reason that the Vararam leans out the system is because the air molecules which the MAF is measuring no longer accurately correlate to the actual quantity of air molecules entering the engine. This is an important concept because it identifies the true purpose of the MAF. The MAF does not actually count every single molecule of air which passes across it. What it does do is measure how much the air that passes across it cools down it's sensing element(which has it's own theory of operation). Based on some thermodynamic theory and data logging, the ECU programmers then develop a model which correlates the temperature drop to the oxygen mass flow rate. This model is called the MAF transfer function, and this is what needs to be adjusted whenever a piece of hardware is installed which effects the MAFs readings.

A lot of people believe that the Vararam increases the turbulence within the intake tract and as a result changes the convective(cooling) properties of the air stream. There is probably some truth to this, as the Z06 guys are getting even more erratic behavior from their Vararams due to the fact that they lack a flow conditioner(MAF screen) immediately upstream of the sensing element. That being said, it's illogical to believe that the Vararam changes what was once laminar(straight) flow into turbulent flow.

To conclude the Vararam issue, the reality is that the intake requires significant changes to the MAF transfer function, and it is my belief that while the ECU compensates for the incorrect AFR during part throttle, at WOT, the car is running leaner than it should be. To dismiss the unit as inferior because of this is pretty narrow minded, but not as much as ignoring the situation entirely. A simple mail order tune (ECS is a great candidate as long as logging is performed) is all it takes to adjust for an otherwise great intake.

rebelheart

Some very good info there!