Terrible Rough Idle, Good MPG = *BLOWN SC gasket*..pics pg 2 - Page 3 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 03-06-2007, 11:07 PM   #21
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on the fedex truck tomorrow..............

oh ya, 1500 posts
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Old 03-07-2007, 03:36 AM   #22
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Well I swapped coils from the GTP and the IAC...it still idles like crap.

We can rule out coils and IAC right now I think.

TPS voltage is solid at simulated idle (engine off) I think we can rule that out, its smooth up to 4.something very smooth, it matches the GTP'* TPS perfectly

So its not the TPS, IAC, Coils, plugs, wires.

I unplugged the MAF sensor..yep it idles worse, it barely runs, plugged it back in, slight improvement.

I then unplugged the vac line at the BCS, plugged both of them, no go, at the time I also unplugged the vac line at the LIM also plugged it. still idles poorly. I also did this with the other vac lines.

This one has got me stumped.

faulty maf sensor? I'll have one from sonoma_zr2 soon since I cannot swap the GTP'* onto my car since its a bit different.

I have a perfectly working 2000 GTP i can swap anything I want from within reason. Throw out any ideas.

I'm starting to throw guesses at CAM sensor, MAP Sensor, EGR, PCM, or MAF sensor. But have no idea and am not going to replace parts until I've confirmed what it is. This is driving me crazy. Jesus there are a lot of things that can cause this. I guess I will continue swapping out parts unless anyone has any other ideas.
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Old 03-07-2007, 07:37 AM   #23
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Remember how I mentioned tearing it down, doing the gaskets and possibly finding the issue then? How about a leaky manifold gasket. You could be burning a little amount of coolant and causing a poor idle.
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Old 03-07-2007, 09:02 PM   #24
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You might try to check for a gasket leak around the supercharger gasket to the intake. I had that issue with an older SSEi and it was a very troubling problem to find. Squirt a little carb cleaner around the base of the supercharger as it is running and see if the idle changes. If it does, you have a bad gasket and a rough idle. It WILL smooth as you accelerate and not evidence a problem at higher speeds. Another thing you could check would be your power brake booster. If it'* sucking air through the diaphram, you'll notice a bad idle as well.
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Old 03-07-2007, 11:56 PM   #25
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Quote:
Originally Posted by carguyblack
You might try to check for a gasket leak around the supercharger gasket to the intake. I had that issue with an older SSEi and it was a very troubling problem to find. Squirt a little carb cleaner around the base of the supercharger as it is running and see if the idle changes. If it does, you have a bad gasket and a rough idle. It WILL smooth as you accelerate and not evidence a problem at higher speeds. Another thing you could check would be your power brake booster. If it'* sucking air through the diaphram, you'll notice a bad idle as well.
Thats possible I suppose, I'll give it a squirt.
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Old 03-08-2007, 12:52 AM   #26
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Hans, you have DEX. You have a problem.

You should be tearing off the top end, replacing all the gaskets, and ditching the DEX.
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Old 03-08-2007, 01:08 AM   #27
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You should also check to make sure your EGR system is working properly.

Quote:
EGR is typically not employed at high loads because it would reduce peak power output, and it is not employed at idle (low-speed, zero load) because it would cause unstable combustion, resulting in rough idle.
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Old 03-08-2007, 02:24 AM   #28
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when I spray tb cleaner on the back of the SC the idle changes dramatically and the car wants to die.

I replqaced the vac lines on the top..still doing it when I spray, either there is a crack in that little cylinder thing on the top or the supercharger gasket is blown out.
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Old 03-08-2007, 06:21 AM   #29
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yep the supercharger gasket is blown out.

i spray near it and the engine dies. base of the SC near the back center.

WTF. good thing I'm ordering a SC gasket from INTENSE when I do the LIM gaskets.

The vacuum leak is big enough to stall the motor completely and to kill engine vacuum probably 80% since I get no HVAC. I noticed this today. I'm like f*** yeah its a vacuum problem

is 3:30 in the morning and I'm out for the night. I'll be sure to get pics.

the hiss is not too loud, but you can hear it if you put your ear on the SC.
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Old 03-08-2007, 07:32 AM   #30
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Where is the leak, you mention back of the SC....however that'* a little vague.

You had previously mentioned spraying before and not finding the issue. Cool beans that you went further and found the leak. BUT.. let'* make sure it'* your SC gasket and not another small part hanging off the SC or a vac line. For the SC to leak that badly..I'd wonder if it'* torqued down.
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