Another 95 Yukon question - bog off idle

Wouldn't hurt to take off the EGR and see if the pintle is seating properly. Although you can test the diaphragm to see if it moves freely while it's still on, it's always a good idea to look into the intake passageway to see if there is alot of carbon built up in there.

I've had them plugged so bad, both the intake and head was packed full. If it was that bad, you'd likely be pinging pretty good.

Check the throttle shaft to see if there is any up & down/side to side play. Even though they are a sealed bearing, they can still get sloppy.

Did you ever get a fuel pressure reading? If you have a rubber fuel line near the filter, might be easier to tap into that for the pressure gauge. I don't know why GM couldn't be bothered to install a Schrader valve up top?!?

I know the 94 and 95 GM's can be a pain to get scanned. Many have that goofy OBD 1.5. I've been running into that on a bunch of GM's of those years.

If you're also getting real bad mileage(ok....worse than usual) - check to see if the coolant temp. sensor is responsive. A bad or coated one will make it run real fat. Either doesn't get into closed loop or takes forever getting there.

 

I meant to take one out to open up the exhaust and drive it. If it seems better the convertor may be suspect. It would be odd to be RPM/throttle position related, but wouldn't hurt to eliminate the exhaust system.

 

The Schrader valve on most of the truck TBI units, if I recall correctly, were located in the fuel line coming up the backside of the engine.

 

Not throttle body. you have to tap the fuel filter spot. spider injection was the one with a valve. cats would cause it to dog under load. i still vote vacuum leak. Unless you have plugged every port and sprayed ether all over then determined its not leaking vacuum into the crank case. but That's just me

 

you might try clamping the return line and see if it helps any. TBIs are supposed to run on 13-15 psi, but they will run with much less, as little as 5 psi. Poorly, but they will run.

 

I would try removing the vacuum line to the egr valve, plug the line and see if it changed anything. An egr valve opening to quickly will cause this. It's going lean for a few seconds. Does it idle high or rough? Another common problem was the throttle body gasket cracking and causing this issue.

 

When you set the timing did you disconnect the tan w/black wire to put it in base timing mode? It's either under the cover on the pass. side firewall or inside the truck under the pass. side dash area.

 

plug all the vacuum ports including booster. and pull the oil fill cap off and see if there is vacuum in there. what rpm is it idling at? the linkage that hooks up to the throttle body hasnt been messed with has it? ive seen people screw them out to raise the idle maybe someone has messed with it? or the plastic cracked.

 

I've never seen an L03 or L05 come with that valve.

Wouldn't be too hard to drill and tap a fitting between the TB and fuel lines. Then add a gauge. They have kits that come already done.

 

You guys wiould know better than me. My memory is not what it used to be.

 

Glad you finally found the problem......and let us know.