Idle problems

[tomtom72]

Originally Posted by ernbuild

Thanks Tom have a bit of time today and hope to check a few of these items out. However the high idle is right from start up ,not once it warms up. What ever is the problem has no effect on performance once moving along, but can be a Pain in the a#SE IN TRAFFIC.

Ahhhhh Ha!!!! Now I have a sympton that I can use as a starting point, thanks Ern!

Okay, go get a very rigid 3-ring loose leaf paper binder. Then remove the air duct from the air horn. Start the car. Take the binder and place it over the air horn, Hang On To It really tightly as the LT5 will suck it in if given 1/2 a chance....our motors like to move that much air. If the motors stalls out quickly then you do not have any vacuum leaks past the point of the binder. That's good. Then go look at the Dowel diagnostic down below for testing the 2* t-blades to see if they are seated correctly.

If the motor does not stall out but looses some rpm then you have an alternate air source. Good luck as they can be a right PIA to track down if it's a collection of small ones. Just need to make sure that the binder seals well against the air horn.

You can do this in addition to the above scientific diagnostic procedure...........with the air duct removed and the motor at idle use a soft wood dowel, 1/4" dia., to push against the 2* t-blades. If the idle goes down then that "Dag" that I spoke of has been compromised. You can maybe do the same with the 1* t-blade, but ya need a really small dowel as that blade is 19(?) mm. That is to say that the vacuum leak is really an air leak thru the 1* &/or 2* t-blades at the "Dag". Now if the trick with the 2* blades has no affect on idle speed, and the loose leaf binder said you got no air(vacuum) leaks; then you have to suspect the IAC or/and the primary T-blade. The 1* t-blade has an adjustment screw to check and I'm sure it must have a "Dag" ring also. Now confession time: the idle screw I have no idea where & what to do....and the only way I know to check the "Dag" s to dismount the T-body and look for it from the back side of the blades. You maybe be able to see it with the motor off and all the blades at WOT position. Oh, also check the TPS for correct voltage, 0.54 volts @ 0% throttle (throttle blades closed), motor running at idle.

I hope that this may give you & your mates a direction to start from. Also, with the loose leaf binder....hold on tightly and expect that after about 30 seconds or sooner it will start to fold up and get sucked down the air horn! This ain't like the old days of carbs when you could cup your hands over the air horn or use a shop rag to cut the air flow to check for a vac leak.....our LT5's will ingest that stuff. All this BS with dowels & binders is due to the fact that a scan will not show any of these t-blade issues in the scan results, the only thing a scan tells ya when ya have a vac leak is that the MAP voltage is wrong.


Tom