Hi Guys,
Reggie,
If the calibrator is still set correctly (around +14 on the low and -16 on the high should be about right for your car) and the tech changed a few bad components as you had mentioned, here's what I'd look into.
First, make sure the tech reset the PCM by disconnecting the battery. If he changed the components and did not erase the old settings from the PCM, the car will still drive a little off until it relearns.
Second, once the battery has been disconnected and the memory erased, you'll have to teach the PCM the throttle range of the Throttle Position Switch. Do this by turning the key to on, and press the gas pedal to the floor, hold, release full and repeat once again. This will show the PCM the range the throttle travels in. Until you show the PCM where 100% throttle is, itwill think 100% is just the highest you've had it before. This is why some cars pickup more power on their second dyno pulls also. The driver did not show the PCM 100% throttle on the way to the dyno.
Third, I'd look into the fuel you have in the car. Poor quality fuel can cause surging at low throttle loads on Speed Density Fuel System cars (Viper).
Hope that helps.
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Rick Martino:
Reggie,
I think your problem stems from the current programming of Roe chip previously installed. That chip feeds inputs to the idle air control motor located next to the right throttle body. It has a 1" hose running to the air filter housing. At idle it regulates the amount of air coming into the intake manifold while the throttle plates are almost completely closed. These inputs affecting idle speed are engine coolant temperature, throttle position, crankshaft position, brake switch and air conditioning request signals. Poor programming of this chip may allow too much or too little air coming into the intake manifold, via this route, necessitating manual adjustment of this screw.
If the factory paint seal was broken on the adjustment screw then whoever installed the chip may have had to mess with it to smooth out the idle.
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Rick,
The idle RPM is preset into the factory PCM and our calibrator will not alter that RPM. The engine will always go back to what the PCM is set to regulate it at. There is also a runner cast into the intake manifold that connects the two intake plenums so that both sides are seeing the same volume of air / vacuum at idle. If one throttle body was open a bit more than the other, at idle, the idle air motor would still regulate the RPM to the preset, but it would probably open the air passage less to do so.
Our VEC1 alters the load calculation of the PCM and this occurs at "load". The greater the load, the more it can adjust the load calibration. Load calibration of the PCM controls how much injector duty cycle percentage and spark advance the engine is given. If we take this adjustment outside of the range the PCM expects to see, the PCM will set a trouble code and the engine will run poorly. Therefore, we have a voltage clamp on the system that keeps the user adjustments in check. No mechanical adjustments are necessary to properly set the calibrator.
The VEC1 corrects the times when the PCM is giving the engine too much fuel / too little spark advance or too little fuel / too much spark advance under loads. This applies to both stock and modified engines.
