Idle drop on initial start up
 

On initial start up the truck drops to about 500 RPM and then picks back up to idle. I have taken apart the throttle body and cleaned it and have fiddled with every adjustment possible on it. I know I have something adjusted wrong because the idle screw on top is all the way in and the tuck idles at 900-1000 RPM warm. I have fiddled the auxiliary air valve on the bottom of the TB. If I screw it too far out the truck does not to do the idle drop, but then it idles too high and the idle screw is still adjusted all the way in. I think that I might have a vacuum leak somewhere, but is there something I might be missing. The truck is a 94 22RE

The truck should idle at about 750 warm, not 900-1000, which iis more like the cold idle speed.
given that the truck idles low cold and speeds up when warm, I'd suspect the cold start switch or injector aren't operating properly and the idle-air valve under the throttle body is stuck 'open'.

I'm sorry, let me re phraze everything. On start up the truck fires, goes from 1500 quickly to 500, then to 700-800, then up to 1200-1300 cold idle. Once warm it idles at 900-1000, with the idle screw adjusted all the way in. I have messed with the auxiliary air valve screw in an attempt to remedy this problem. I guess while writing this I realized that maybe i have been trying to handicap a broken cold injector with a vacuum leak? But I originally started fiddling with the truck because it would drop to 500 RPM after throttle.

I didn't realize there was an adjustment on the aux. air valve for those years. Hmmm....

Kirk......does the cold start system continue to operate after start up until it reaches operating temp, or just on intial cold starts?

I just went out to the cold motor, started it and un-pluged the cold injector and it made no difference in idle speed

Okay.....with the idle bypass screw all the way in, start the truck from a dead cold start. Before it has a chance to warm up, turn the aux air valve adjustment all the way closed. The motor should just about die or even die altogether. Make sure the throttle plate is closed, too.

If it doesn't die, you have a vacuum leak somewhere.

I should be able to put a piece of tape over the hole right. Should I buy a cold injector, I have ebay up and I'm about to

Yes....a sturdy piece of tape will work.

Hold off on buying the injector. I don't think it's your problem. Unless you like buying unneccessarily....:D

Of course, then you'd have a spare. So, it's not a real loss.

BTW, you said there's an adjustment for the aux air valve. Where is that located on your throttle body?

on the auxiliary air valve if you take that plate off secured by 4 Philip screws there like a spanner nut with a valve underneath it that I have been taking the throttle body off and on to adjust. Im going to go put a piece of tape on that hole and unplug the injector and I will reply with the results

Okay. If it doesn't die, try spraying some ether around the vac lines and the TB and cold start injector.

so at first cold start it jumps to 1500, then down to 500, then up to 1200-1300, then warms up and settles at 900-1000... and unplugging the cold start injector doesn't affect it....

well... first thing I'd do is make sure that the bellows (the rubber fittings on the throttle body and air flow meter) don't have any cracks or other breeches- the clamps are tight, and nothing between the throttle and air filter is disconnected.

depending on the ambient temp, the cold start injector may not operate- basically, over 80F it won't do anything since the temp switch that controls it doesn't think 80 is cold. it is literally a 'cold' start system. the stock EFI can figure out most normal temps... if the coolant temp sensor (in the coolant passage on the manifold) and air temp sensor (located in the air-flow meter) don't give it extreme readings.

regardless, if you can't get a warm idle down to 750, there is something wrong, likely either a vacuum leak or a problem with the idle-air valve (auxillary air valve) under the throttle body.... possibly even the throttle plate is being held open (due to a binding cable or the 'dashpot') and it's even possible that the throttle position sensor is malfunctioning.

OK. Tape over the hole: truck would not idle. I adjusted the Idle air screw to keep the truck running. I unpluged the cold injector, nothing. adjusted the idle lower, unpluged it again. nothing. So the injector is bad right? Still, what would cause the low idle after start or after throttle? do I need to replace the injector then readjust everything? what on earth is causing my idle drop though after warm up off throttle?

so you bypassed the IAV / Aux Air Valve and had to adjust the idle screw on the throttle body out to keep it running?
sounds to me like you've almost found the problem.

under normal operating conditions, engine warm, etc....
the IAV / AAV is CLOSED, so given that you taped over its passage and things changed... implies to me that it is at least part of the problem

well how do I adjust it. It looks primarily mechanical like nothing could really go bad

you don't adjust the IAV/AAV, you replace it.

It's thermal wax, so over time it can stick open or shut. Or, poor coolant flow to the valve can give the same effect....like air bubbles or a blockage.

Yeah...that's the same thing 91Toyota ran into.

But what about that spanner nut I'm fiddling with, thats an adjustment. where do I go from here?