1995 L27 Silhouette - Surging idle at warm start-up - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 09-24-2007, 01:27 AM   #1
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Default 1995 L27 Silhouette - Surging idle at warm start-up

It'* done this since I bought it and I've had trouble figuring out why.

When I start it while the engine is warm (100* or so), the idle will fluctuate by about 1000 rpms but will not stall. If I give it a little gas it will smooth out.

I've reset the computer
Cleaned the TB
Cleaned the MAF
Cleaned the EGR passage
It has a new fuel pump, intake, EGR, coils, ICM, o2 sensor, plugs, wires, PCV valve, air filter and fuel filter.

No codes, stored or otherwise.

It runs pretty good otherwise. Other then what sounds like an exhaust leak (I'm thinking cracked rear exhaust manifold on that) and possibly a bad harmonic balancer (which I planned to replace next month).

Any ideas?
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Old 09-25-2007, 02:02 PM   #2
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Old 09-25-2007, 09:20 PM   #3
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When you cleaned the throttle body, did you clean up the idle air control valve and passage really well? Check for vacuum leaks, also.
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Old 09-25-2007, 10:05 PM   #4
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I'm having the same problem with my 4.0. I have to ask, have you had any issues with difficulties starting the car? Or does it fire up after 2 or 3 cranks, then surge?

MAF cleaned, IAC cleaned, TB cleaned, air filter fine, fuel pressures fine

**subscribes to thread** because I'm at wits end.
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Old 09-26-2007, 01:22 AM   #5
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Quote:
Originally Posted by Archon
When you cleaned the throttle body, did you clean up the idle air control valve and passage really well?
Yes, I had. Clean and shiny.

Quote:
Originally Posted by Archon
Check for vacuum leaks, also.
I suspect there are a couple, but I haven't had any luck finding it yet.
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Old 09-26-2007, 01:27 AM   #6
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Quote:
Originally Posted by Jim W
I'm having the same problem with my 4.0. I have to ask, have you had any issues with difficulties starting the car? Or does it fire up after 2 or 3 cranks, then surge?

MAF cleaned, IAC cleaned, TB cleaned, air filter fine, fuel pressures fine

**subscribes to thread** because I'm at wits end.
It turns over very quickly (2-3 cranks) and starts surging. No hesitation on starting.

Does yours start hard? My 3.4 DOHC Cutlass does and I know the injectors aren't leaking because it still does it even if I hold the pedal to the floor. I'm suspecting wiring problems there.

I just went through the cold surging with the DOHC. It had a chunk missing from the plenum gasket!
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Old 09-26-2007, 10:08 AM   #7
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A can of carb or TB cleaner is your friend at finding vac leaks. This sounds very much like vac leaks.
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Old 09-26-2007, 11:18 PM   #8
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Quote:
Originally Posted by BillBoost37
A can of carb or TB cleaner is your friend at finding vac leaks. This sounds very much like vac leaks.
I'm leaning towards that now as well Bill. Thanks!
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Old 09-26-2007, 11:43 PM   #9
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just L67 swap it....
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Old 09-27-2007, 12:15 AM   #10
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Yeah, I have the same problem periodically. I am gonna try and track it down with tb cleaner around the vac lines. We'll see.
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1995, 3800, 95, carb cleaner, oldsmobile, series 1, series i, silhouette, throttle body, vacuum leak

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