1990 stick won't idle

black V8

Registered User
Hi Folks, my 90 stick has sat for a couple of years with occasional starts and moves around the yard. The last few times I moved it it dies if you don't feather the peddle. Sounds like it has a miss too. Once up to 2000 or so rpms it smooths out. Also when revving it it initially pulls a vacume till the revs get up then it goes into boost. Is this indicative of a vacume leak? I haven't pulled any codes yet, no engine light on and I haven't road tested it yet other than down a long driveway where it behaves fine till I push in the clutch and it dies. Car is stock. I will pull out a very basic code reader I got with the car years ago and try and figure out how to use it. Thanks.
 
Just hooked up the code reader and got 67, 82, 67, 82, 10, 29.

67, neutral pressure switch circuit failure, circuit open.
82, air diverter solenoid circuit fault or supercharger bypass circuit fault.
10, ?
29, insufficient input from VSS, or insufficient input from programmable speedometer/odometer module.
 
67 is a 'Continuous' code; Clutch Switch circuit failed (3.8L SC only) - See: http://www.njtacc.com/tech/eec_codes.html for SC specific code listing.

Ignoring 29, for now, (10 is a null/place holder, not a code), 82 sounds like maybe the bypass is sticking/stuck open...problem is, I thought only the '89s had a 'bypass solenoid'. Does yours have any electrics associated with it? Looks like this, but I don't know where it sits:
attachment.php


If you do have one, I think it's ok to eliminate it. Factory put them on early SCs to defeat boost in reverse - that 'feature'/cirsuit wasn't used in later models. My '90 doesn't have it, as an example.

In any case, I'd take a look at the bypass to start...know where it is/what we're talking about? Back of the supercharger, there is a vacuum pot with linkage that opens/closes the bypass plate.

When the car is idling, it should be pulled opened all the way and when the car is off, it should be closed, on the stop, same as when under boost. Check it's position engine off, then start it up and watch the lever to see if it moves. Confirm the vacuum line is intact/in place. Maybe it's stuck open, or the vacuum pot is history/leaking.

Pulled this image from another thread....the arrow is pointing to the vacuum pot.

attachment.php


This image shows the plate, similar to a throttle body:
attachment.php
 
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Thanks for the resonse KMT, I'll look tomorrow to see if I can see a bypass solenoid. The vacume line on the pot on the sc was in place and intact but you've given me some things to check tomorrow in the daylight. Thanks very much.
 
Finally got a chance to look at this, the linkage from the sc bypass pot is sitting about an inch off the stop when the car is not running. Tried to push it against the stop but it won't budge in that direction, will move in the other direction though. Will have to take some things apart and see if the plate is jamming somehow.
 
Ok, so a little more background that I didn't think was necessary. Car sat for a couple of years because of a coolant leak at the lower rad hose and also thought it might be losing some from the water pump, I have other vehicles so was in no hurry to fix. Last few times I moved the car it would stall but otherwise ran smooth. Got my boss's nephew who is a mechanic to change the waterpump and hose for me in my yard which he did over a couple of evenings. The first evening he got it apart but didn't finish so he pointed out to me that he was stuffing shop towell in the tube where the intercooler hooks up so nothing would get in. Wellllll, yah you guessed it, he got things back together but on startup rough and smoking and to keep it running I really had to rev it. Ran codes as stated above, from that and KMTs advise started looking at the sc bypass. As I said earlier the bypass lever was sitting an inch off the stop. So today I wrestle with the rubber connector just before the bypass and pull a fibre shop towell out of the damn thing. Now at least the bypass closes properly but still running ragged. I'm assuming it may have sucked more effing shop towells in.
What sort of damage could I be looking at?
 
'running ragged' could mean any combination of things. Do your best, if you haven't already, to recover the entire shop towel to see if you can account for most/all of it. No telling what path the towel took if it was torn up. Could have gone straight into the intake manifold and engine, or taken a ride thru the supercharger.

I'd pull the belt off the supercharger and see how it spins by hand - easy enough to do, just swing the tensioner and drop the belt at the SC. If it complains, I'd be tempted to remove the supercharger top so I could inspect the rotors. If the towel made it past the supercharger, bits could be plugging the intercooler, so if that seems likely, you may want to yank it and look inside.

Not sure I'd run it again until I knew more about what's going on internally. Might need to pull the plugs and do a compression test to see if any valves are bent/stuck open. Not easy to do, but with the plugs out, you could use an inspection camera to check the valves, etc.

If you can account for the whole towel, tho, might just be it's not happy from sitting (plugs/wires) and/or you've got some whacking good vacuum leaks....if the intercooler tubes were loose, do you know what the process was to re-seal them on assembly? They can be a chore to get sealed again, and if they leak, the engine will run ragged, for sure...ask me how I know ;) Fingers crossed that's all that's wrong.

Remember, an alternative to firing the engine after dealing with vacuum leaks is to smoke test it.

Tough one...good luck.

Ken
 
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Thanks KMT, I'll pull the belt on the sc later today and give it a spin. He used rtv to reseal the tubes, I'll ask him today how many shop towells he stuffed in there but he's a gd stoner so who knows. Shoulda just did it myself. Dang!
 
Here is a pic of the route a towel in the lower IC tube could take...

bypass.jpg

Yellow is air flow path out of the intercooler. The red arrow is the bypass. When it is closed, air goes down into the intake manifold, then into the heads. The small black dot on the edge of the cutaway, left of the brass bypass plate is the intake temp sensor - might be it could catch the towel on the way by, so I'd want to remove it to inspect.
 
Well I finally got back to this. Looked at the intercooler couplings and realized top and bottom were only finger tight. Pulled it all apart, cleaned mating surfaces off, reapplied rtv and snugged up, let it sit overnight and snugged just a touch more and started it. Bingo, she's now running great. Well besides a broken spring, rattling end links and needing brakes but got an order in with Rockauto.
Thanks KMT for your guidance, much appreciated.
 
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