I can see where it would be easiest to not undo the fuel line. I wasn’t sure about the washers that were used, and there was a faint hint of fuel smell so I replaced all of the washers for the fuel rails, injectors and CSI just to be sure. (Then I went crazy with the CSI bolts, but my heart was in the right place.)

Any idea why the timing mark would be shifted to the right by a few inches when I hit it with the timing light? It worked fine before I changed the timing belt the second time, so I must have screwed something up. I have the timing at a generic middle of the road setting for now, but it should be set properly. It’s as if the whole range of timing has shifted. I can’t adjust the distributor enough to bring the mark into the scale in the timing cover, and the engine runs like crap when get toward either end of its adjustment range as you would expect.

 

Idle timing cannot be correctly set unless the TPS is accurately set, and idle RPM is in spec.
Improper TPS and/or high idle RPMs can make the timing appear out of whack.

 

I checked the TPS when I had it off the engine and then again after I put the throttle body back on the plenum. It takes a little while to get up to temp, but once the truck’s warm it idles smoothly at 800 rpm. Does the angle of the timing light matter? That’s the only thing I can think of that I might be doing wrong. The cable has to stretch from the spark plug wire on the passenger side over to the driver’s side, and I really don’t want to get it snagged in the belts, so I was shooting the crankshaft pulley at an angle. Or can I clip the timing light anywhere along the spark plug wire to cylinder one? I’ve tried to put it as close to the spark plug as I can.

 

Everything's all back together. The timing is set correctly (my earlier problem was because the timing gun had the advance set wrong). I'm down to one last issue, the engine idle. On a cold start, the truck will idle around 1500 while it warms up, but it will only drop to around 1200 when it's hot. If I stop the engine and restart it, then the idle drops down to around 850, so I can't use the idle adjust screw on the throttle body to solve the problem. When it's idling high, I can completely close it, but then the engine will stall when it's restarted.

I've tested the TPS, replaced the idle adjust screw and o-ring, replaced all the vacuum hoses (and a vacuum leak would happen all the time so it doesn't fit the symptoms), cleaned the throttle body, and checked the air intake for leaks. I thought it might be a problem with the AC or PS idle ups, so I've disconnected both of them and capped the vacuum lines. I've checked the cold start injector and it's functioning properly when the engine is cold, and I replaced the CSI gasket. The only thing I haven't directly touched is the idle adjust valve on the throttle body, and I suspect that this is the problem.

Has anyone seen a situation where the valve can intermittently get stuck like this? I don't see where restarting the engine would break it loose. My understanding is the valve is operated with heat sensitive wax like the engine thermostat is. When it's cold, it shrinks, opening the valve to allow air through. When the coolant heats up, the wax should expand and close the valve to block the air flow. If the valve were marginal, could the time it takes to restart the engine give it just enough time to properly close if it couldn't when the engine was running? I'd hate to pull the throttle body off if I don't need to.

Also, are there any parts available for the idle air valve (specifically the wax piece)? I checked with Toyota, but they don't seem to sell throttle body components other than maybe the dash pot (which is out of production). Without parts, what are my options for fixing things if the problem is with the idle air control valve?

 

I resolved the idle issue. It turns out the dash pot was sticking, so the engine would only come back to full idle it I left off the accelerator for a minute or two, giving it time to compress the dash pot. I removed the spring from the dash pot assembly and it idles correctly all the time. Thanks everyone for all the help.