I have a 98Z that I just swapped a LS3 into and everything went fairly well for my first ls engine swap. It fired up on the second or third revolution of the engine and it runs awesome. Only problem is it wont idle below 1800 rpm. When it gets that low it acts like I turn the key off. I have a fuel gauge on the fuel rails and it has 60 lbs of pressure. I haven't had the computer reprogrammed yet. Kind of afraid to drive it like this. Do you think it is in the program or maybe something that I missed when I swapped it? Thanks for any suggestions!!!

 

Do you have any MILs? Also, are all the ports on the throttle body plugged? Sounds more like a vacuum leak or a bad TPS.

 

maxharvard, All the ports are plugged, I have a new TPS, new AIC, and I have tried spraying carb cleaner all around to find a vacuum leak. Don't think it is a leak. And I don't know what MIL's are. Thanks!!!

 

MIL - Malfunction indicator Lamp AKA - Check engine light.

Some things to keep in mind, new parts do not equal 'good'. So don't trust that because it's new that it works properly.

Secondly, pull off the air intake tube and see if your throttle body is completely closed with at idle. It wouldn't shock me if your throttle cable was too tight.

If that is closed at idle, make sure your connections are good to the IAC and TPS. Does your intake tube have the air temp sensor installed? Then if that's good, hook up a scanner to see if you have any codes showing.

 

I'd grab a scan tool and check your IAC's and TPS voltage. It's been awhile since I did it on my LS3, but if I recall correctly get your hot IAC's in the 45-70 range by opening the throttle body set screw, then reset your TB voltage. Also ensure your TPS is absolutely 0 and not fluctuating at idle.

 

I have checked and I have slack in my throttle cable. I have unplugged and replugged in both the IAC and the TPS several times to make sure they were making good contact. The air temp sensor is installed and I also checked it several times. I checked for trouble codes and I forget the number that the code showed but it had to do with the clutch and transmission. I have a turbo 350 so that can't have anything to do with it. I didn't feel like messing with it today but I will look at it again tomorrow. Thank you for your input sir!!!!

 

Thanks Jim, I will look at this in the morning..... and let you know.

 

Had it a bit wrong, here are more details I found in my notes:

1) Ensure your TPS voltage range is correct. It should be near .6V at idle and between 4.0 and 4.75 at WOT; higher than 4.75 can set a DTC. The typical fix here is to slot the TPS sensor bolt holes slightly so you can rotate the sensor clockwise or counterclockwise to get it in the correct range and then re-tighten the bolts.
2) Get the car up to full temp... >175degF but with fans & A/C off. Check IAC counts in the scanner. We need them to be between 40-75ish counts. If the counts are HIGHER than this, you need to slightly adjust the throttle body's blade screw in the direction that OPENS the blade. If the counts are lower, we need to CLOSE the throttle blade a bit. If you end up having to open the blade, you will need to reset the TPS. To do this, key-off, unplug TPS, turn key-on (run not start) for 10 secs, key off, plug round 3pin TPS connector back in. At idle when you start the car, verify 0% TPS in scanner (not 0-1 flickering or anything but all 0%). Once this is done, the car *should* idle pretty well on it's own when warm at least.

 

Actually.... it might. Who programmed it? Did you tell them this was your transmission choice?

 

I haven't had it programmed since I installed the ls3. I don't want to drive it till I can get it to idle. I might have to put it on my trailer if I can't get it to idle. It has been a little bit cool here so I haven't been in a hurry to figure it out, but I will post back when I figure out something and let you know what I find. Thanks!!!

 

Well that might be half your problem honestly.

Where did you get the motor? What was the original tune? I'm not sure I would run a motor that I didn't know what the tune was.

 

Uh, are you running a 58x motor with a 24x sensor and computer? You must have flashed it somehow, or it wouldnt start at all. An LS3 has a 58 tooth reluctor.