Fatdog2

Attached files .Is this the one?Thanks.

GaryDoug

I am not the expert that Fred is, but again the only thing I see is that the IAC is bottomed out with the idle rpm about 70 above the target. I assume it's a manual transmission because of the low target (550). In general the IAC is doing the correction ok. You can see the down-slope while the engine warms up. But after the engine is warm, it can't close off anymore, stuck at 0. Might be a small vacuum leak.

The second file is fine. I don't know what happened to the first file, not good.

Injuneer

Manual trans is programmed higher..... 800 RPM fully warmed up. Auto is 550 in gear and 650 in neutral.

Try to take a look tomorrow.

Fatdog2

Please ignore the first log as this was a test that went bad I think.Finally got the program dialed in (I hope) on the 2nd test.By the way it's an auto.Many thanks again.

Injuneer

Finally downloaded the second file. I'll try and get to it later today. Just taking a VERY quick look at startup, nothing looks out of line.

Sorry for the delay.... retirement is more time consuming than working......

Fatdog2

I appreciate all you are doing.No rush.I'm just curious about what GaryDoug mentioned about a possible vacuum leak.These cars are old and I've replaced some hoses and vacuum leaks seem to be an issue with these cars anyway.Again,I appreciate you generous input to CamaroZ28.com.

Injuneer

It seemed to take a long time to warm up enough (140*F) to enter closed loop. Do you have the correct LT1 thermostat installed - either 180* or 160*?

Preliminary look at the extended idle at the end of the log, and in the idle cell (16) it's suddenly getting rich O2 readings, and the PCM starts to pull out a lot of fuel. The would seem to suggest something other than a vacuum leak is causing the IAC valve to bottom out at "0". I'll take a look at periods where the EVAP purge is active, to see if there are any signs of vacuum leaks there. But EVAP is not used at idle.

I'll keep reviewing.

Fatdog2

When I had the radiator flushed at a goodyear store they bloched the job when the new radiator hoses were installed and I was loosing coolant and they couldn't find the problem but I took your recommendation for another member and rented (for free) a pressure tester from Autozone and the hoses were squirting everywhere so I fixed that.Anyway I said to the mechanic 3 times that the new thermostat must be 180 degree one for the LT1 engine.I bet they jacked me on that as well.I'm going to replace it just for the piece of mind in the near future or sooner and see if that will make a difference.Again many thanks.

Fatdog2

This small vacuum leak has caused some concern here as I thought I figured out I had paid enough people do find out what was the issue and after I had done all the gas filter,plugs, wires,throttle body cleaned,wrenched all the screws and bolts,and after throwing parts here and there on the car and running techron with every fill-up that somehow someway a little rough idle would go away.Then,I watched some videos on utube and I (in my infinite wisdom)Decided,what the hay.I'll just throw one of these on just for kicks.It's a hobby car . So I bought a brake booster check valve ac delco of course,threw it on there(the hose has no leaks) and some of my rough idle has smoothed out a bit.When I put my new rear shocks on I'll do a little inspection of the evap system back there and see what I can find.Sorry for the long post.The video I like the best is this guy threw some stuff on the car only to find this issue.(U-tube----1985 chevy caprice brake booster check valve----and another great video---brake booster check valve replacement---
I think Shoebox brought this up before but I can't remember.Hope this helps. Myo2(Maybe it was Injuneer?)

Fatdog2

For the past year I've been chasing down a vacuum leak ever since GaryDoug mentioned this in a previous message.I've learned to operate a ohm meter,a fuel pressure tester,a vacuum tester,pulled the injectors out for cleaning and testing, I did replace the injectors because of all the bad stuff I've read and heard about the stock ones.Checked 90% of all wire connectors and vacuum tested every hose for leaks all the way back to the canister and back to the engine.Checked the wires (most)coming from the computer to the engine and some were melted together but checked out ok I think.
Well,to make this story longer,I've been reading this(Vacuum Leaks and the LT1)by Charles O'Toole 2004 over and over again for the past year. I followed the instructions about the throttle body top plate gasket and replaced that last year but to no avail.After re-reading about the throttle body gasket he mentioned sealing the gasket with some sealer.After a few beers and the engine starring at me (my work bench is 6 feet from the car) I removed the top plate and sealed the gasket on both sides with permatex form a gasket and let it dry a couple of days and 80% of my rough idle is gone.Thanks for reading.Hope this helps someone.

Fatdog2

Also,when I flush my coolant this summer,I'm replacing the coolant sensor in the water pump like Injuneer suggested.(New one sitting on my shelf for a year now).
I did replace some grommets including the one in the pass. side valve cover for the hose going to the throttle body, well the plastic elbow doesn't quite seem to fit tightly.Charles O'Toole mentioned that there is a ribbed plastic elbow that works better.Anybody heard of this before?This might seal better I think.Many thanks in advance.

Injuneer

There is not a lot of "vacuum" present in the line from the throttle body to the valve cover. If you look at the front of the throttle body, there is a hole in the "roof" of the TB, in the top wedge between the two throttle bores. That is the starting path for air to flow into the chamber on top of the TB (the part under the top cover you carefully sealed), then out the top (larger diameter) connection on the passenger side of the TB, into the line to the valve cover.

In effect, the air entering that line comes from in FRONT of the throttle blades. As such, there is very little "vacuum" (negative pressure) present. Air starts at ~30"Hg outside the air filter (at least at sea level). As it flows thru the air filter, there is a little pressure loss. Also a little loss from the friction of the air intake tubing, loss when the air changes direction, loss when it encounters a sudden expansion or contraction.

The total loss between the "outside" air and the air in front of the TB blades, assuming you have a clean air filter is probably only a couple "Hg. Almost all of the outside air pressure is still there.... very little in the way of negative pressure. The real "vacuum" is caused by the pressure lost as the air passes through the throttle blades. Closed blades, there can be a loss of ~18-20"Hg, leaving the air in the intake manifold at about 10"Hg. When the blades are fully open, there is very little pressure loss in the flowing air, meaning pressure in the manifold and the pressure in front of the throttle blades is roughly the same at ~28"Hg, or only ~2"Hg vacuum.

Point is, there is really not much in the way of a vacuum leak at the TB top plate, or in the elbow on the valve cover. Bigger problem at the TB top plate would be a small amount if dirty air entering the engine through the TB.

The line from the TB to the valve cover is designed to be "neutral".... because it has to be capable of flowing in either direction, depending on the state of the PCV system. The crankcase is operated under a slight vacuum. The vacuum source is the C-shaped rubber hose connected to the PCV valve on the driver side of the manifold. That vacuum pulls clean (filtered) air from in front of the TB blades, through the line to the valve cover, down thru the oil drainback holes in the cylinder head, sweeping through the crankcase to pick up piston ring blowby. That mixture flows up thru slots in the sheet metal pan under the intake manifold, thru a passage built into the manifold, out thru the PCV valve, where the vacuum from the C-shaped hose (93/94) on the PCV valve dumps it into the plenum of the intake manifold.

If there is excessive piston ring blowby in the crankcase, and pressure starts to build, the pressure is relieved by the blowby flowing "backwards" up thru the head and out of the valve cover to the throttle body, where it also gets pulled into the plenum.

Lot of BS.... but don't worry excessively about the top plate gasket or the grommet/elbow in the valve cover. If you can find a slightly larger or ribbed (barbed) elbow, fine. If not, neatly wrap some rubber electrical tape around the elbow to make it a tighter fit when you insert it.

Fatdog2

Thanks again Injuneer.Great explanation.While I had the intake elbow off I did spray some throttle body safe cleaner on the blades and tooth brushed them at the same time as the top plate.The blades didn't seem dirty but I cleaned up the throttle blades where they are attached(pivots) real good.Maybe?

gaedbo

Fatdog2 you may want to take the throttle body off and thoroughly clean it for peace of mind. It is fairly easy to do, and then you would have confidence you did all you could do to help with your problem. When I did mine I was amazed at how contaminated it was. I was really glad that I did it, the gasket kit is pretty cheap, around $13.

The other thing you may want to consider is not using the Air Foil. It can limit the amount of air flow from the throttle body to the passenger side valve cover(depending on which one you purchased). There is only a couple of H.P. I believe that the Air Foil is able to gain you.

Good Luck to you.

Fatdog2

I've been contemplating cleaning the TB off the car, I think you are right.
What method did you use to clean yours?
I watched a video that this guy used Chemdip carburetor and parts cleaner.
Not sure this is safe for the TB.Many thanks.