Last year I purchased a '86 GT with a '95 3800 SC Series I. It ran ok except overheating due to bad head gaskets.
This spring I took the engine/trans out of the car for the head gaskets replacement. In addition I took apart the supercharger to clean it inside, grease the rear needle bearing and replace the coupler. The engine swap appeared to be pretty old, at least 10 years, maybe even closer to 15 or 20.
It has the '3800 SUPERCHARGED' Fiero Pegasus decals and additional body work intakes. So there were some rotted vacuum lines that I had to replace, and determine the correct routing the original builder used.

This morning I started it up for the first time since putting it back together. It has a very high idle, so I can not run it for any length of time for fear of causing damage.
The throttle cable appears to be at it's closed position without any tension on it.
Not real familiar with superchargers, I am not sure if it is vacuum issue, a SC bypass valve issue, etc, or some other issue I am not thinking of.

To me the very high idle almost seems too high for a vacuum issue, but I am not certain about that either.

Thank you for the help on this.

[This message has been edited by hdryder (edited 10-12-2014).]

Go back over every vacuum line, every fitting and port.
Check that the blade on the TB is properly closed.
Check for an open port somewhere.

OK good, thank you. I will make those checks.

Does anyone know where I can locate a vacuum schematic for a '94-'95 3800 SC Series I?

Thanks again.

How many vacuum lines do you have on it?

LIM vacuum (the port that is under the snout of the SC) goes to the fuel pressure regulator and the BBV if you have it.

Vacuum between the SC and the TB - runs to the power brake booster, the BBV and the Evap Purge Solenoid if equipped.

Take out your IAC and stick your finger into the hole covering the hole completely. Start the car and see how it idles. If the idle is low or it won't idle at all - look at IAC problems. If the idle is still high and the throttle valve is closed then you have a vacuum problem.

btw, a small vacuum line won't make the engine run 2500 or over. Only a large vacuum leak will do that. A large vacuum leak won't can't come from a small vacuum port.

[This message has been edited by phonedawgz (edited 10-12-2014).]

Just throwing it out there, not sure if the series I is setup the same way, but check the injector o-rings for vacuum leaks. I had a vacuum leak that had been chasing for a long time and I finally found it there. Check EGR tube if your still running EGR, mine was cracked ever so slightly.Check the EGR valve to make sure its clean and not stuck open or something. Check to make sure your EVAP is setup correctly if, you are still running it. My vacuum leak was so bad at my injectors that blocking off my EVAP which was setup totally wrong and was a constant vacuum leak, would not even show up until I fixed the injectors. Good luck and keep us posted on what you find.

[This message has been edited by zmcdonal (edited 10-12-2014).]

quote Originally posted by phonedawgz: LIM vacuum (the port that is under the snout of the SC) goes to the fuel pressure regulator and the BBV if you have it.

I am trying to locate this port under the snout of the SC on the Series I.
I see this port on my Series II intake manifolds, but not my Series I manifolds.

Could it have another location on the Series I motor that I could look for?

I do have a Boost Bypass Valve, which I had to replace the little 45 degree preformed hose because it was rotted.

The car also has an automatic trans. which uses a vacuum line. It was pretty much plugged up with a rusted steel tubing in it when I first took it part. I replaced that hose at plastic check valve location.

When replacing a supercharger, a careful system of torqueing the mounting bolts in sequence is required for a leak free seal. Did you torque properly use a sealer and follow the torque sequence properly? I would shoot smoke into the intake and with a bright light look to see if any is escaping. You can easily make a smoke generator with some incense, a jar with a lid , a couple of fittings, some vacuum hose and a small air compressor.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Powerlog manifold, Northstar TB, LS1 MAF, 3" Flotech Afterburner Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by Dennis LaGrua: Did you torque properly use a sealer and follow the torque sequence properly?

I didn't use a sealer on the s/c base gasket, but I would be willing to give that a try if it would resolve the problem.

I have not found a torque sequence diagram, but I did start in the middle and did a X pattern towards both ends.

Just removed a Series 1 from mine a few weeks ago. From pistons up are fine if you want them. Gen 3 charger from 1995.

You are right about the series 1 not having the vacuum port under the snout, just series II and III.
Sometimes there is a port facing the front/firewall on the throttle body that can have a plug in it or have a vacuum port. Mine had a vacuum port.
There should be 2 vacuum trees one is right next to the bypass valve and one closer to the throttle body. The one near the bypass is manifold pressure. That's where you want the pressure regulator and trans modulator. There they also get boost pressure. The one closer to the throttle body is after throttle vacuum. This is where you want brake booster(big port)and accessories(evap, cruise, etc.)
The M62 chargers have a habit of getting leaks under the snout where it meets the lim.
Most vacuum leaks will cause the engine to lope/surge because the leaking air is not measured by the MAF.
If the engine is just screaming up in rpm, it would be better to expect sticking open throttle blade or stuck open Idle Air control. Those would be measured by the MAF. The finger test in the IAC works well, but have someone else start it up while you put your finger in the hole. (man that didn't sound right)

[This message has been edited by cmechmann (edited 10-29-2014).]

quote Originally posted by cmechmann: If the engine is just screaming up in rpm, it would be better to expect sticking open throttle blade or stuck open Idle Air control. Those would be measured by the MAF. The finger test in the IAC works well, but have someone else start it up while you put your finger in the hole. (man that didn't sound right)

Thank you for all the good vacuum port information. I have been going through that and it seems to be in order, but I will check again this weekend using your information.

I just pulled the throttle body off to check it further, and see if the throttle blade was hanging up. It looks ok, and I cleaned it before I put it back on last time, but I am going to clean it up again, including pulling out the IAC to check and clean.

Thank you all for the help on this one. I would like to get it running soon, so I can put it up for sale.

I have the IAC valve out of the TB, and it and the hole was pretty dirty. Cleaning both.

Is there a way to bench test an IAC valve while it is out of the TB?

Also, anything I can check on the Throttle Position Sensor (TPS) while the TB is off the car?

Thank you for the help.

You can do resistance test on the IAC. Last time I checked, should be 40-80 ohms terminals a/b and c/d. Should measure open a/c a/d b/c b/d.
There is a way to run the motor in and out, but without the right setup, it normally would shoot the pintle out and you would have to put it back together.
It's best to have a pulsed tester for that. And if voltage is held too long can burn the coils. Terminal A should be neg. B positive for one direction. Terminals C neg. D positive the other direction. Most GM PCMs will run the IAC all the way in and back out after a memory reset to find it;s range. when you first turn the key on after reset. If the IAC is not in the throttle, the pintle is run out beyond the stop and again you would have to put it back together.
The TPS is easier in the car. You don't really need to know what pins are what. With TPS disconnected, key on, voltmeter should measure near 5v at one pin in the harness, ground at another. The left over one would be your signal return back to the PCM. Reconnect the TPS connector. Use a paper clip to "backprobe"(making contact through the weather packing) the signal return. The the throttle closed should read near .5v, full throttle near 4.5.
That is not as important as making sure that the voltage doesn't drop out or spike while slowly moving the throttle from closed to open. If it does, that shows a bad spot in the sensor. Drop outs/spike normally show up just past the the closed position (5-15%). That's where the throttle spends most of it's time while driving.

OK, great. Thank you for that test information.

I just read in the Chilton's GM Electra/Park Avenue/Ninety-Eight 1990-93 Repair Manual that there were three different designs of the IAC conical valve.

Design 1: Single Taper
Design 2: Dual Taper
Design 3: Blunt Valve.

It looks like mine is the Dual Taper design. New replacement IACs at AutoZone are $57.99

I just remembered I have a spare Series I M62 blower with a Throttle Body on it, which I plan to take a look at. I hope it is a Dual Taper design also.

I removed the Throttle Body and cleaned the IAC valve. Now the engine is still racing at a very high speed at startup. I can't even run it long enough to determine the RPMs in fear of blowing up the engine.
It seems to be running much faster than any vacuum leak would cause.

With the throttle plate completely closed, how can and engine run at such a high speed?

For testing purposes, will the engine run if the Supercharger belt is removed?

Thank you any and all help.

1 - Perhaps the IAC pintle is too retracted and stuck. Extend it some, but make sure it does not bottom (overextend) in the throttle body bore and get jammed when re-instaling it.

2 - Perhaps you created a huge vacuum leak when removing the throttle body.

I'll go with 1 to start with.

Air IS getting into the engine. Throttle plate, IAC or other vacuum leak.

Try this - remove the IAC and unplug it electrically. Then stick your finger in the IAC hole. If you can by blocking off the vacuum side of the IAC hole reduce idle below the target idle speed then the problem is going to be with the IAC.

Next - With the same set up as before - finger in IAC hole with engine running - plug in the IAC and see if the pintle moves in and out to try to adjust the idle. The PCM should extend the pintle when the idle is too fast and retract the pintle when the idle is too slow. Note - if the pintle over-extends it will be released from the IAC and will launch across your garage floor and fall into the floor drain. Block the pintle from over-extending by blocking it with your hand. Note again - it is perfectly ok to block the pintle from over-extending. That is exactly what happens all the time when the PCM resets the pintle in the throttle bore. You won't burn out the IAC by doing this.

IF THE IAC ISN'T MOVING - Again with the engine running and with your finger in the hole to control the idle speed - check for voltage to each of the IAC wires per the video. When the idle speed is above or below target speed the PCM should be pulsing power to those two wires.

Note also IACs rarely go bad, so don't start with replacing it.

[This message has been edited by phonedawgz (edited 11-18-2014).]