Hello all,

I am new to the world of TBI. I recently swapped a 92 TBI 350 out of a Chevy K2500 into my 85 K5 Blazer (Yes, I know it's not an F-Body ). Here is the problem, it wont idle at all. I can get it started by manipulating the throttle, it will run REAL rough and then smooth out. However if I let my foot off of the throttle, it dies. While setting the timing, I noticed that the throttle plates dont move at all when cranking it.

I take it from my searching of the board, that this is not normal. I read the instructions for the IAC, but they read like an Astrophysics for Geniuses book.

Can someone help me bench diagnose this?

Thank you for your time,

Joshua

 

have you scanned the codes. Mine was doing the same thing but maybe not to the extent of yours. It turned out my vaccum line to the MAP sensor had come unplugged. Have you checked your fuel pressure to see what that is at. Do you have a good spark. Whats your base timing at? Did you set the timing with the EST unplugged. Just a few things to check, hopefully youll find out what it is. Good luck

 

Fuel pressure was at 13psi, base timing is at 4 Deg BTC with the wire disconnected. All vacuum lines look good... Also, I have not scanned any codes, however the SES light hasnt tripped.

 

When you swapped motors, did you take the TBI unit off and clean it at all? Over time a lot of carbon builds up in the TBI unit and can gum up everything, especially the port for the IAC valve. I would try that first, take the TBI unit off and clean it with carb cleaner as good as you can, and clean out the IAC valve and inspect it.

Generally, if a TBI motor is having a hard time idling at a stop, it's usually a vacuum leak or the IAC valve is bad or gummed up (this is just what I have observed, this is not a fact). It may also be a good idea to check the TBI mounting gasket and make sure that it's torqued down properly to the manifold. I second the suggestion to check for vacuum leaks.

 

No, I didnt clean it as it was a running motor... I can do that today.

 

Did the entire setup come together? i.e. Are the computer and harness from the 350 setup as well? Does the SES light light up when you turn the ignition to the on position? If not, you may actually have a code, just not know about it.

Other than that, check what the others said, maybe even play with the base timing a little more if your fuel pressure, iac and vacuum checks out ok.

 

One other thing to check as well is the voltage going to the injectors as well as the fuel pump

 

No, it was all seperate... How do I check for the code?