'76 FI idle problem.

[Velokid1]

As you all know, Colin and I installed FI onto my bus last weekend. Fired right up, really need no adjustment at all, which was lucky since we ran out of time and he was going to have to leave come hell or short pants.

Ran great all week, then I changed the oil yesterday and when I started it back up had problems. Here's the sequence of events, spelled out plain-like cuz I'm an ACVW clutz and am sure I did something that affected the idle:

1) After Colin left, idle went up a bit. So I adjusted the idle from 1000 RPM to 900 RPM by turning the idle screw on the throttle valve body.

*When we checked the dwell last weekend, it was perfect, right at 45... when I checked the idle, dwell was at 38. I did NOT correct this.

2) Swapped my plugs for new ones. The old were in fine condition. A tad black but acceptable. Double-checked the gap on all, .028". Started engine again and checked spark by removing wires one at a time. All OK.

3. Changed oil. Spent 90 minutes gently chiseling with a blade and screwdriver to remove the petrified strainer-oil pan gasket. LOL Changed filter.

4. Started her up, immediately heard a vacuum leak. It was the coveted Y-connect that goes from the aux reg. to the plenum. Our jerry rigging made it crack open (or me fumbling around in there did). Fixed that vac leak. Started her up again and the idle was all over the place, up and down and sputtering. Not backfiring.

-When I would open the throttle quickly, it would bog.
-If I opened the throttle slowly and ran the RPMs up, it would throw black smoke and sputter, sorta backfire.

5. I checked all hoses, used the stethoscope trick. Thought maybe I heard a vac leak down around where the throttle body meets the plenum, that gasket there. Not sure I was hearing correctly though. Pulled the S-boot off and tightened the throttle body/plenum connection with a screwdriver... replaced air cleaner and S-boot.

6. Started her again, still idleing rough. Felt myself getting pissed, went inside for a sandwich.

7. Came back out, warmed her up and decided to drive her to see how bad she was really running... she sputtered first 50 yards, then ran fine. And idled fine. Hmmmmm.....

8. This morning it was about 45 degrees out and I let her warm up for about five minutes in the driveway. When I came back to her she was warm but the idle was just kinda going up and down by maybe 25-50 rpm. Just enough to be discernible. Drove to work and everything was fine. Once up to full operating temp, idle was steady.

Any thoughts?

[DurocShark]

You have a vacuum leak still. You also have a leaky injector (you said so in another post).

Cold roughness but smoother after warm can be the TSII.

[Velokid1]

I drove it to lunch today and it went fine for about a mile, then I actually had an episode where it started bucking/stalling/sputtering so I pulled onto a side road, went back to have a look. Decided to try to get it home and... it ran fine.

OK, maybe I need to double check the throttle body. (I tried spraying around it and other possible leak locations with carb spray, but it did nothing.)

Can the throttle body bushings wear out like on a carb, causing a vac leak?

Are the throttle body-plenum gaskets still available?

Does a leaky injector cause the sort of symptoms I'm experiencing? How does that work?

The Temp Sensor II is brand new, so I doubt it's that.

(Thanks, Duroc)

[steve74baywin]

Yep,, most often it ends up being a vacuum leak...
You did say the dwell changed, that could have made the timing change, which then could have gave you the increase in RPM's.
But it stills sounds like a vacuum leak......

[dingo]

make sure your A.A.R is closing fully when warm

[Randy in Maine]

Adjust those points to the sweet spot. 47º +/- 3º. What are you setting the timing at anyway?

Sample the resistance in the Temp Sensor II just so that we can rule that out. Hook it up when it is cold and leave it on as the engine warms up to see that it is indeed changing resistance.

Remove the vacuum connection to the brake booster/decel valve and put duct tape or a cork in there to remove that entire line from the vacuum system equation.

Remove the vacuum line going to the EEC valve on the aircleaner and put a golf T in there. If you have no charcoal canister for fuel vapors, leave the golf T in it.

I put a dusting of Hylomar (or wheel bearing grease) on the seal between the throttle body and the air plenum. Made me feel better.

Measure the resistance between the 2 terminals at the aux air regulator to see if you are at 30 ohms. 30 is good, 0 and infinity are bad.

Fire it up and commence spraying the Gum Out carb cleaner to see where that pesky vacuum leak is. Sometimes you have to give it more gas to get better suction to get the Gum Out in the system.

Get back to us.