bad idle/missing

[butlar]

car revs fine, but only when revved fast. I have a new set of fic 750 injectors, new plugs and wires(gapped plugs .028), great compression and timing is on, also no boost leaks. The only thing i havnt changed it is the fuel filter. My mods list is up to date just to let everyone know. The car when revved slow or held at a certain rpm stuters every second or soand engine shakes pretty severly, this is in neutral. Car is in my garage on my lift, so I havnt driven it yet, because i dont think it is driveable the way it is. Any help would be appreciated.

 

[pedrick1]

well if you are saying that the car revs fine when applying gas but bad at idle and you say the engine shakes pretty violently that sounds like a tps (throttle position sensor) problem. My engine used to shake pretty bad at idle but would rev nice and smooth, i replaced the tps and problem was gone.... http://vfaq.com/index-main.html there is a vfaq in there under INTAKE on how to test the tps to see if the voltage is within spec

 

[butlar]

it only seems to rev fine if i give it a quick shot of gas. If i gradually give it gas or hold it at a steady rpm it shakes and shutters and misses, i have another tps , maby i will try that one.

 

[pedrick1]

yea try the other tps and make sure when you take the one you have on there right now off that you mark it so when you slap the other one on you wont need to adjust anything

 

[Talesin]

No idea if your EPROM replacement is set up to compensate for the difference in global deadtime on the larger injectors, or if it just alters the fuel maps. Usually that tends to be the biggest problem people run into, with cheap chips.

 

[butlar]

It is a keydriver stage 3 chip from dsmchips.com , with injector compensation, so i would hope it is set up correct.

 

[butlar]

update: have not had much time to get at car, but i noticed that logger shows 8% throttle on TPS even at idle, not giving car any gas, so I would assume the TPS at least needs and adjustment and/or replacement.

 

[pedrick1]

yea, easy fix

 

[Talesin]

TPS reads that due to the ISC. It's actually at 8%. An SAFC will show zero percent because it's showing a list of 'seen' percentages, instead of the ACTUAL throttle position, and calculating the throttle position off of that.
Your TPS is likely fine, and working correctly. Mine usually idles at ~11% throttle.

PS- This might be obvious, but you're going to get lumpy/funky idle with 272 cams. Only other recommendation is to make sure your AFPR is set to 36psi with NO vacuum (should drop to ~27psi once you hook the line up again) and that your MAF-T is zeroed. Might also want to take a look at your GM MAS. People do have problems with those things if they're incorrectly installed, or just have bad luck.