LTFT is weird......help!

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Gau8mechanic

New member
My '97 LSC likes to stall once in awhile. Happened twice going down a hill - both times decelerating to parking lot speeds. Happened twice backing up - both times backing into my driveway. Doesn't stumble or shudder. Just turns off. Restarts fine. The instructor I have in my auto tech school has an Autel Scantool. He hooked it up and we looked at my long and short term fuel trims. LTFT on passenger side is dead on zero. LTFT on driver side is 5.85%. We thought vacuum leak. Sprayed carb n choke cleaner around the back side of the intake and it immediately reacted and dropped to -12%ish. Started to stumble as the computer tried to readjust trims. We repeated this twice. Used a smoke machine too but smoke only came from the intake airbox. None from anywhere on the engine. We suspect the upper and lower plenum gaskets. Does anyone have some insight on this that could help me better assess this?
 
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Gau8mechanic

New member
102K. Is there a fix out there? I heard the seals are no longer available without buying the whole spacer with the IMRCs installed.
 
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Neil

New member
It sounds like you have way more resources to work with than most of us here. You are lucky!

I would put the straw in the can and try to isolate the exact area sprayed when LTFT's stabilize.

Others have dismantled their IMRC's and improvised seal repairs. I would get a used set and take my time rebuilding them if that turns out to be your trouble.

Good Luck,

Neil
 
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Gau8mechanic

New member
Just changed out the lower manifold gaskets and the IMRC to head gaskets. Cracked the throttle body mount gasket. Ordered a new one from Rockauto.com(Fel-Pro) since not one dang store here carries them in stock. What is the name of the oval shaped gaskets that go between the throttle body runner part of the intake and the intake itself? I cleaned them and reused them since I can't find out the name to order new ones.

The IMRC's were CAKED with crap! I spent nearly 2 hours cleaning them alone and they still have stuff on them. I think it's time for a BG44 or a Seafoam treatment to clean the whole upper portion of the engine. It's all back together though and runs like a raped ape! Idles smoother and takes less pedal to get her humping from the line. I'll check the LTFT when I get back to school in the morning.

As far as the seals, I'm assuming the seals are at the front of the IMRC? Neither end had any evidence of leaks. Just a caked up ring right where the butterfly closes against the IMRC body. Now that that is all scraped off and cleaned, I presume they can perform much more efficiently. We'll see.......
 
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