Idle adjustment on 4.3 TBI

**1great40** · 06-17-2013

Hi again guys. I'm doing pretty good with my 4.3 40 Ford pickup thanks to a lot of help (and patience) from you guys. My idle is still sending resonant vibrations through the truck but if I crack the throttle just a bit and raise the engine speed, it's pretty good in the cab as far as vibration and resonance.

My understanding is that the idle speed is hard coded into the PROM so there's no point in trying to set the speed with the minimum air adjustment. Is there any electronic way to make the idle adjutable?

Thanks again

**EagleMark** · 06-17-2013

Min air won't do a thing for idle RPM. It's all in the chip.

**1great40** · 06-23-2013

I feel like a kid on Christmas morning, you know, when you get something you have been wanting for a long time? No, not that, get your minds out of the gutter, I already did that this year.

I found the source of my idle vibration problem!!! As I had mentioned, there was a chirp sound when the truck was placed in gear, every time it shifted and sometimes over bumps. Once in gear, the truck would vibrate...the hood, the fog lights, the steering column, everything. I have been poking around under the truck looking for the chirp, hoping that the chirp and the vibration would be one in the same.

The big problem is that chirps come in all shapes and sizes and it takes a skilled chirp sleuth (which I am not) to out the offending problem. I checked everything I could see and then finally started on things I couldn't see and had to assume were OK.

There is a spot where the passenger side exhaust pipe connects to the manifold that's directly over the right frame rail. You can't see a darn thing in there but I used a ty-rap as a feeler gauge and saw that I had maybe .040-.050" between the pipe and the rail. I had also developed an exhaust leak at that connection. I hauled up on the stud nuts and since, even with a mirror, I couldn't actually see the clearance, I decided to make more room by shimming the rear transmission mount 3/8 of an inch.

I started the truck and put it in gear and voila! It idles pretty much the same in gear as it does in park! No more vibration

I'm still going to try isolating by exhaust system with some new style rubber exhaust hangers to further isolate stuff from the body and frame but so far, so good. The truck is becoming more of a pleasure to drive every day. I still have a rattle in the glove box door to fix, a squeak that I think is associated with the hood latch and somewhat of a clunk on severe bumps that I have to chase down but this was the biggest bullseye I have hit yet!