rough idle and slight decreased power after warm start - 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 04-05-2008, 02:50 PM   #1
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Default rough idle and slight decreased power after warm start

well the subject line pretty much sums it up. I read a post about something similar but it appeared to be a boost issue. here'* what it does:

the car has been taking just a little longer to start when cold (not necessarily COLD, but after it'* been off overnight)

once it'* been driven and engine brought up to normal temp, say if I shut it off to run into walmart, the car will not have a problem starting, however, once it starts, it'* spitting and sputtering below normal idle, and the volt meter is down close to 8-9.

THEN, I'll rev it up a few times and things will be back to normal for the idle, but once I get going it hesitates and has decreased power for at least a few minutes...but then it returns to normal.

The thing is, it only does this once in a while. Sometimes I'll start it and it'll be just fine. No codes either, so besides thinking it could be a fuel issue, I'm basically at a loss.
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Old 04-10-2008, 07:41 PM   #2
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Default I have a similar issue

I have a 1993 SSEI bonneville, it runs fine when you first start it up, then when it warms up it runs rough, I have new coils, new wires, new plugs, new supercharger, new amsoil and just got the transmission flushed and new filter and oil. Now when it runs for about a half hour, when you give it gas it stalls then surges back up to idle. When you barely give it gas it runs fine until you push down on it, it almost cuts off. What could be the problem. I ran on a scanner and came up with an odd code saying "quad error" or something on a SnapOn Scanner. Also when the needle gets almost around 1/2 - 1/4 tank it will stall on braking.
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Old 04-10-2008, 09:40 PM   #3
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Default

Had the same issues recently; crapping out on acceleration, shuddering with mild acceleration in OD, spitting and sputtering at idle in Park. Prime suspects are Plug wire, spark plug, or coil (or multiples there of).

The quick check to find the cylinder is:
  • -Start engine; allow to stabilize; unplug IAC motor (not to exceed 2 min.); use insulated pliers (AND a rubber glove is great too); pull one plug wire at a time while listening for miss to get worse or stay the same.
    -If the miss gets worse, that is NOT the cylinder
    -If it stays the same, that is the indicator of the bad cylinder
    -You can have more than one.
    -Mine was 2 bad coils. But they had been passing the resistance checks until the morning I went out and it started missing after I started it. That is when the coils completely went out.
    -If you have a volt-ohm meter, you can check across the output side of each coil. They should all be close to equal. Of course, if it reads open, the coil is shot.
Hope that helps
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Old 04-10-2008, 09:56 PM   #4
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Default Re: rough idle and slight decreased power after warm start

Quote:
Originally Posted by CJCroel
once it'* been driven and engine brought up to normal temp, say if I shut it off to run into walmart, the car will not have a problem starting, however, once it starts, it'* spitting and sputtering below normal idle, and the volt meter is down close to 8-9.

THEN, I'll rev it up a few times and things will be back to normal for the idle, but once I get going it hesitates and has decreased power for at least a few minutes...but then it returns to normal.

The thing is, it only does this once in a while. Sometimes I'll start it and it'll be just fine. No codes either, so besides thinking it could be a fuel issue, I'm basically at a loss.
I need to work on my reading skills. The fact that it is intermittent may be a bad connection, ground or battery cable issue. I don't like that part about the volts being so low. That alone can drive you control systems nuts. Make sure your battery connections are clean on BOTH ends. If yours is like mine, it has 2 positive cables. One goes to the starter; the other up to the relay/fuse center on the firewall. There are at least 4 ground points under the hood; 1 on each front fender plus 1 on each of the 2 large stud bolts that are used for mounting the ICM to the block. It is also common for the +12v cable to corrode INSIDE the sheath, usually nearest the battery. Have to slit and peel back the insulation to check this latter thing.

On my 93, the PCM grounds at one of those studs under the ICM. It was bad about working loose. The battery ground to the block is on the other stud.
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