Idle problems

[tomtom72]

No problem Ern! I'm a building super, so I'm not a mechanic either!

Okay, stupid Q: do you have the Helm Factory Service Manual set for your 90?? If not go here to see about getting a set.

http://www.helminc.com/helm/homepage...3K60N8W4KU4NV4


Tom

[ernbuild]

Dont have the Helm, but do have a set of factory manuals. Will they have the required info ?..

[tomtom72]

Originally Posted by ernbuild

Dont have the Helm, but do have a set of factory manuals. Will they have the required info ?..

I would think that the FSM set that you have will have a section for "Emission's & Driveability". That is where the diagnostic flow charts and aids to diagnostics are in the Helm set. I would guess that most of the other manuals like Motors & Chilton's...etc are mostly laid out the same way, I would suspect??


Tom

[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.

[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

[ernbuild]

Thanks Tom will try that today. Missus way/layed me yesterday and ended up sanding the deck and sealing it. Will let you know how I go. Ern.

[ernbuild]

Well tried a couple of things. First up could not get the engine to stall by blocking the throttles off as you suggested. In fact it made very little difference to the revs. Tried a few things to cut off air flow, including a rubber sheet a quarter inch thick. However was able to lower the idle by the adjusting screw right at the back of the mechanism that the cables attach to. Damned awkward, 8 mm nut on threaded rod with an allen key on the end to turn the screw. Managed to get it down to 900 to 1000rpm, but its still surging about 200 rpm. Its a lot better than it was but still has a vac leak by the sound of it. What do you reckon?? cheers Ern.

Originally Posted by ernbuild

Well tried a couple of things. First up could not get the engine to stall by blocking the throttles off as you suggested. In fact it made very little difference to the revs. Tried a few things to cut off air flow, including a rubber sheet a quarter inch thick. However was able to lower the idle by the adjusting screw right at the back of the mechanism that the cables attach to. Damned awkward, 8 mm nut on threaded rod with an allen key on the end to turn the screw. Managed to get it down to 900 to 1000rpm, but its still surging about 200 rpm. Its a lot better than it was but still has a vac leak by the sound of it. What do you reckon?? cheers Ern.

You are masking the issue when you adjust the set screw. That set screw was set by Rochester and MM never touched them when they assembled the motors.

By completely closing off the air intake, you eliminated any possibility that the TB was the issue. My guess is you have some leaks in around the fuel injectors at the injector housing.

[tomtom72]

Jeffvette = The West Coast LT5 Tuner, Sensei Master....

So it's "what he said, man!". No BS.

Did you have the injectors out? Seems like the prime suspect would be the large O-rings that are inside the I/H injector ports. In any event the air isn't coming from the T-body.


grasshopper

[ernbuild]

Yes Guys the injectors were out, however all new O rings when it went back together. By the way the engine was apart 18 months ago, and was running ok till a few weeks ago. Have monster headers fitted, and relocated the O2 sensors further away from the engine. Also no cats, and burns a little oil at start up. Will check O2 sensors as well, as read also if they have a build up of gunk can cause surging. Will keep you advised. Thanks again for all the info guys, cheers Ern.