Intermittent TBI Idle Issue

[Daveo91]

Among some other challenges I have with the tune for my vortec 383 TBI is an intermittent issue where it won’t register as an idle when speed is zero. Causes it to stay in closed loop even though I have the timer set at 12 seconds to go into open loop idle. Also causes a high idle of 750 or 800 even though commanded is 650. Also exacerbates my decel issues that is my other big tune problem.

Happened today on next start after a 30 mile drive. (Two hour delay after 30 mile drive and next start). I was lucky to have my laptop with me so I plugged it in and saw that idle status was not registering even though vehicle was not moving and PCM showed 0 mph vehicle speed. What would cause the idle status to not get set even though speed is zero? VSS? Loose connection somewhere? Ground? Note that shutting engine off and restarting resolves the issue - at least it has the few times this has happened in the past. I’d say it happens less than 1 in 10 times I start engine.

[In-Tech]

Is tps voltage above .6v? Is it moving around at idle?

[Daveo91]

Is tps voltage above .6v? Is it moving around at idle?

Thanks, good idea. Kicking myself since I only monitored for a new minutes before I shut it off and restarted and forgot to check that. And I didn't log while it was doing it. When it's running normally TPS voltage is pretty close to 0.5 and not jumping but maybe when this is going on it's behaving erratically. I'll just keep an eye on it.

Any other ideas?

[In-Tech]

What ecm? There are many things that affect closed loop idle and not just talking about o2 closed loop. There are other idle control strategies mainly "unforseen" especially in the 7747 if that is what you are working with especially if you have changed the desired/commanded idle speed in the cal.

I'm sure we'll all help if we can, just need a bit more info.

-Carl

[Daveo91]

What ecm? There are many things that affect closed loop idle and not just talking about o2 closed loop. There are other idle control strategies mainly "unforseen" especially in the 7747 if that is what you are working with especially if you have changed the desired/commanded idle speed in the cal.

I'm sure we'll all help if we can, just need a bit more info.

-Carl

Sorry, it's a '7060 PCM. And I think I'm pretty much stuck with that stock unit since it's an early (91-93) 4L80e. Here's my other active thread right now - and that thread has a link to my intro thread.

Yeah, I kind of gave up on closed loop idle - it would idle fine for a while and then it would start hunting. I have the timer set at 12 seconds to go into OL idle - rock steady once it's there. Works great, except when the PCM thinks the vehicle is still moving and won't go into idle status.

[In-Tech]

Thank you for the added information. Pardon, I might have read the details in another post but I think you said you are using a 454 tbi, can you reply with info on what year 454 injectors you are using and also your fuel pressure?

Thanks,
-Carl