Ron_H

For the past 3 day weekend I spent the time retracing my steps and discovered 5 glaring faults either caused by me or present before I got into this project. All of them would seem to have some negative effect on smooth running and even running at all!
The first discovery was huge. One of the rubber hose joints between the plenum and intake runners had a large long tear in the rubber and was letting false air into the system. Things get old and fail. I had no access to new parts at the time and didn't want to take the bus to work this morning so I patched that hole as best I could. A new one is ordered along with some extra hose clamps because mine are not functioning to loosen or tighten.
The second was a big one too: two of the intake runners were only hand tight at the intake ports. That one is on me and I had to stand in the corner for fifteen minutes as punishment.
The next one is enough to anger me, because the injectors had been rebuilt not too many miles ago. One of the injectors was missing the ceramic or plastic spacer that goes on the injector before the rubber O ring and cap. So the O ring was free to move around. But that was only the beginning. I had not pressed the injectors into their ports and they were certainly letting air into those ports. I could lift the fuel rail up without any resistance whatsoever. More time for me standing in the corner + writing on the blackboard I will be more careful with the injector placement in the future. By this point I was beginning to wonder how this engine started and ran at all last week. Amazing. But now I knew why it hadn't idled at all either.
Next I found a couple of errant vacuum hoses, one of which was easily replaced in the correct location. One however is confusing me and perhaps someone who knows could identify the correct termination of that hose. It is the one that comes off of one of the two metal tubes protruding from the top of the throttle housing. I have attached a schematic of the vacuum hose system as a reference. The route in question is the one with the heavy dashed line from the throttle body housing to whatever is at the other end. My engine has a short length of hose from that port and is capped off! I know that is not right.
Any suggestions would be appreciated.
The next compromise with which I dealt was the WD 40 I had used to lubricate the hoses and rubber seals around the intake runners and the throttle body to intake "T" tube. I wiped them all down and reinstalled them relatively dry. I couldn't get all the slippery stuff off but I got most of it. Then I made certain they were all tight.
Next I was going to replace the throttle position sensor, but having tested it with a new one last week and found the readings to be exactly the same, (and because I was tired and lazy), I let that part remain in place. I think this may have been a mistake as became obvious after starting the engine yesterday afternoon. The engine did indeed run, and 90% better that last week, but still has an unsteady idle or no idle at all. The stability of the idle is intermittent. Then it occurred to me that the performance of the throttle position sensor could also be intermittent and happened to be on when tested but off at other times. That will be the next item to be replaced after I take it all apart again for the umpteenth time next weekend. The engine has a lumpy idle or dies at first requiring me to use my left foot for the brake while I keep the rpm above 1000 until I can slowly let the rpm drop to 800. Then it will almost keep idling most of the time. Or it will get extremely lumpy before it gets better and evens out. It is simply dangerous to stop in gear because the engine wants to lope and lurch forward if in gear and around idle. I suspect the throttle position sensor or could it be the computer itself?
I must do more homework to solve this persistent gremlin.

James Bailey

You had me worried there for a moment I thought it was a big terminal screw up....if it is just a do over that is just humbling and NOT catastrophic fail. Hang in there you will get it

GregBBRD

Sounds like you need to remove the entire intake down to the heads and start over, cleaning, inspecting, and replacing the pieces that are defective. You've been banging your head against the wall for over two weeks on this problem. About time to quit fishing and just drain the lake.

Ron_H

Yup! I can only spare time on the weekends IF I have no other pressing work in the office, so the next encounter will involve complete removal of the intake system and replacement of the throttle position sensor, plus inserting the one broken throttle body support in the valley that broke free from its epoxied position.
Then careful reassembly with new intake parts that have been ordered and I'll bet the idle will return to normal. Once past 1000 rpm, the engine is smooth and powerful but is not getting full throttle, so I'll get to that also.

I'm still curious to know what that vacuum line is meant to serve though, in case someone knows????

WyattsRide

The longer vacuum line that you have dotted goes from the valve that is connected to the A/C kickdown. The other end terminates at the Thermo Switch (TS). The TS is near the Idle Stabilizer Valve. From the TS, the shorter dotted vacuum line goes to one of the connections on the Throttle Body (TB). The other connection on the TB is for the vacuum line coming from the 7 way connector at the back of the engine. The vacuum line in the front of the TB goes to the EGR.

Ron_H

Thanks Rick. I'll go search for the thermo switch next weekend when I get into the replacement of the throttle position sensor.