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I just started my swap for the first time: Stock 2004 Avalanche (drive by wire) into 1978 Caprice. When I started the car it was idling around 800 or 900 rpm. The pedal is dead and has no response. In looking online, other dead pedals have a series of trouble codes. Mine was throwing no codes at first and then had P0106 code (map sensor). I looked up causes for this and one was "unexpected rpm."
I'm looking into ways to diagnose this, but I'm curious if this could be a tuning issue. I used a PCM from a 2003 Express van. I would think if there were troubles with the pedal components or wiring it would have an associated code.
I did tell the programmer to have it set to drive by wire. I forgot to mention earlier that the last couple of times I started the engine it began to increase revvs quickly so I had to cut it off. Is this how the engine could react if it wasn't changed to drive by wire?
If the engine revs out of control without throttle input you typically have a large vacuum leak.
If the idle is higher than anticipated you may have a small vacuum leak or the calibration was changed by the tuner.
Typically I find vacuum leaks by letting the engine run and listening or spraying some carb cleaner around. If I'm not able to run the engine what would be the best way to diagnose where the vacuum leak is?
That method is fine on an antique engine with a carburetor as it won't run away from you.
You need to make sure all the vacuum ports are plugged, somewhere along the line you missed one.
That was my first thought so last night I went and checked the power brake hose, but it was installed. I also checked the port I opened up for the HVAC reservoir, but it was good. I checked all the fittings that I'm aware of and they all seem to be good. The MAP sensor feels a bit loose. Is this normal? When I touch the part of the sensor on top of the back of the intake (LM7) I can wiggle the MAP sensor around a bit.
It's interesting that the first few times I started the engine it was holding idle where I could at least let it run but then on the 4th or 5th start it started getting faster and faster.
The pictures below show the places I've checked. #1 is the MAP sensor, which wiggles a little. I also have a small fuel leak that I need to fix as well and I mention in case it could be relevant.
See if you can get an 04 PCM. There is no "setting" a tuner can do to make it DBW, They need to rewrite the OS to one that is compatible for an 04. Probably don't have a pedal code, because it cannot even see the pedal to set the DTC. The PCM needs to be compatible with the OS to rewrite the PCM. If they are different part numbers, it may not be compatible and brick the PCM....
I haven't been able to speak with the tuner yet because of the Holidays. I'll get in touch with him and hopefully he'll be able to come over and hook up to the car. The PCM is from a 2003 express van, but the PCM is supposed to have a 2004 Tahoe tune (I think it's a Tahoe, but may be a Silverado). I have found out that the car will quickly rev to about 2000 rpm, but then it does idle back down to 1250 or so rpm and stays there. The exhaust manifolds were glowing red earlier so I cut it off, and it is also overheating a bit, though I filled the system correctly with antifreeze. I think I probably need to get the tuner here before I go any further.
when you say dead pedal is that because it doesn't respond when you started the motor?
did you pull the intake off and see if the throttle blade moves when you move the pedal (engine not running but key on)?
kind of sounds like a bad map sensor if that's what the p0106 indicates... that might make sense if the fuel mixture is that off to heat up the manifolds. you could test it out by putting a multimeter on the signal wire and pulling some vacuum on the sensor. should vary between 0-5v when pressure (vacuum) changes.
maybe could try unplugging the throttle body and starting the engine. the throttle blade should be closed when unplugged and i think the engine would at least idle. if rpm runs away the problem is elsewhere.
Also, does the throttle body move at all when you first turn the key on? It should only move a tiny amount, but you can hear them click as it does its self test. If it isn't doing anything and you do in fact have a 2004 Tahoe tune, then make sure you have power to the TAC module.
But the glowing red exhaust manifolds sounds like a bigger issue to me. How sure are you of your tuners abilities?
Ok, I have an update. People around here are dropping like a civil war reenactment with colds and flus. I got a sinus infection but I'm getting back again.
The issue was that when the tuner put the new OS over it wasn't changed from the van code to the truck code. I can't remember what the numbers were, but it was something like GMT800 or something similar. After I took it back to him it solved the high idle and overheating but I still had no idle. I found a comment on the forum that mentioned you must plug in all the pedal components before hooking up the battery. I unhooked the battery with all the pedal components hooked up and then hooked the battery back up and the pedal worked! So, that was a huge relief.
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New Install: No pedal / Code P0106 
