TBI high idle

[gawain]

First I want to thank the people who made this forum and the many people who post here. Your discussions on engine swaps have helped me a lot on my current project. It's a '66 impala that now has a '93 chevy 350 (from a suburban). The engine runs, car drives, and I'm now in the fine tuning stages of this project.

The problem is the high idle I'm getting. I don't know what the RPM's are for sure, but I'm guessing it's about 1000-1200. I've checked for vacuum leaks and found no indication of such, and also have no trouble codes EXCEPT those relating to the missing tranny and A/C. (A/C is disconnected and the original powerglide tranny is installed) I've replaced several sensors and parts along the way, just to be sure, but I've hit the wall on this problem. Is it possible that the ECM is keeping the idle high because of no signal from the A/C or transmission? (or VSS?) If so, is it possible to fabricate a signal or work some kind of bypass to make the computer think the tranny and/or A/C are still there? Is there something else I might have missed?

Thanks!

 

[llih]

I am just guessing, but I would think that those missing components would cause problems with the ecm. Another good source of info is the tbi group at Yahoo. Some knowledgeable and helpful people there.

 

[ertiself]

first off what year is the TBI if its before 99 its OBD1 and no it cant the tranny gets its control like the 1227427 ecm usely its just 700r4 and is seprate how ever if you have the ecm that has the red and blue plugs on it this is electronic transmission control ecm still no it cant on the idle but the IAC valve in the TBI unit can cause this and there is also the problem that if you replaced the TPS sensor and did not get it on zero it will confuse the ECM that your pressing on the pedle as well and the MAP relates to the TPS and make sure unless your useing a kit and if so ill need more information if this is a conversion a 1 bar is for raceing a 2 bar map is for normal.

there is some things you can do use scan tool look at the TPS voltage it should be 0.5 at idle if it is not and is 1 volts or higher there is the problem zero the TPS so that is measure to 0.5 at idle and the ECM will re sync the map and the idle will come down.

 

[ertiself]

i forgot to mention after reading about the car you have its a conversion ok now this will be diffrent the timeing on this should be 6 BTDC you have to disconnect the EST wire that will take it out of the computer control set the timeing on 6 degrees BTDC then put it back in EST and check what i told you before on the IAC valve and also the TPS if this is all ok and the problem still exist then it could be in the VE tables of the program in the ecm all GM computers can learn in the BLM mode to trick that in action you have to make the computer change the pulse on and off time on the TBI and if this TBI has adjustable fuel pressure reg on it you can use scan tool watch the LT fuel TRIM and the ST fuel trim this you want the LT fuel trim to be 128 the ST fuel trim will change with load this will cause the computer to store the learned sets in its BLM (block learn memory) and it will apply the new sets to the VE table. but if you disconnect the battary it will have to learn it again. but it will do this automaticly once set.

 

[brew8]

vacuum leak, maybe the manifold