Re: [DML] Idle gradually increased to 1700 RPM during warm up
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Re: [DML] Idle gradually increased to 1700 RPM during warm up

Hi everyone

I keep reading the replies and can't help but notice that everyone is 
talking about glowing cats while in the original post we can read about 
glowing exhaust headers. Cats are way down stream from headers, aren't they?
The is a major difference between glowing cat and header. If there's 
unburned fuel being dumped into the exhaust it will burn in the catalytic 
converter and will cause it to glow, BUT if mixture is leaned out 
significantly, combustion temperature will rise and that in turn will cause 
the exhaust header to glow. It will usually start to glow at the first bent 
out of the cylinder head. In this case the catalytic converter will not 

>From the description in the original post I would suspect a large vacuum 
leak on the side where the headers are glowing. That "woooof" sound might be 
a vacuum leak that was heard only when the engine was shut down. The stage I 
exhaust is louder than the OEM exhaust and the noise might cover any vacuum 
leak noise. A vacuum leak might also raise your idle. A rich condition will 
flood the engine and will not cause the RPM to increase.

Dennis, I would suggest that you start looking for a major vacuum leak on 
the intake manifold. Is your car an automatic? If it is, there is a large 
vacuum hose connected to the front of the intake manifold. This hose runs to 
the vacuum modulator on the transmission.
Take a small flashlight and look around the engine. Look for missing hoses 
that might have fallen off, broken hoses, broken vacuum lines, missing 
bolts. Take your time, look around the engine carefully and remember that 
there are hose barbs for vacuum lines on the front of the intake manifold. 
Check the vacuum lines running to the left side of engine bay where the 
charcoal canister is. Make sure to check that large vacuum line going to the 
vacuum reservoir in front of the charcoal canister. Also, remember about a 
large line going to the brake booster!

Let us know what you find!

Good luck

Tom Niemczewski
vin 6149 and 2418, 3633, 5030, 17086 (in Poland!)
Google earth: 52°25'17.30"N 21° 1'58.00"E

----- Original Message ----- 
From: "Mike Polzin" <mikepolzin@xxxxxxxxx>
> I would agree with most of the others assessment that the reason your 
> seeing the red hot cats is that the fuel isn't getting burned in the 
> cylinders, and as a result the gas is getting burnt up in the cats. A 
> quick side note, I don't recommend running your car like this because it 
> is a good way to ruin the cats on this very nicely upgraded exhaust system 
> you have.
> [CUT]
> ________________________________
> From: dmc_5180 <dmc_5180@xxxxxxxxx>
> This is a never before seen problem on my car during my 16 years of 
> ownership.  I went to start the car this afternoon , it had not not been 
> driven since the DMCMW open house weekend  3 weeks ago.   The car fired 
> right up as usual Idle was stable at 775  +/- 25 with a very subtle hunt 
> but virtually stable.  I walk away from the car after 20-30 seconds  I'm 
> letting it warm up.  I was  getting a few things from the trunk of my 
> other car to put in the D. While I had my head in the trunk of the other 
> car The RPM starts to gradually increase on the D. I did not think too 
> much about it Figuring that the Idle Micro switch might not be tripped. I 
> walk back over the D get in driver seat  to see the IDLE is at a steady 
> 1700 RPM .  I tap the Pedal a few times  NO change. OK, I Go back to 
> engine bay to make sure the Micro switch is depressed. It IS. Then I 
> happen to Look down at the Left EXHAUST HEADER. This Is a JET-HOT coated 
> system.  The header starts GLOWING and
> IS increasing rapidly.  I do a quick check of the Right Header which 
> appears to NOT be turning colors at this point. FYI I was in a rather dark 
> building at the time so it was fairly easy to see the heat GLOW.  Well 
> I've never had this happen before. and As the header starts turning very 
> RED rather quickly , I Shut it down immediately.  While the engine was 
> shutting, down I hear a woooof sound in the exhaust, almost like I flame 
> igniting.  The exhaust header quickly turns back to normal color. I wait 
> about a minute then start the engine again. Idle is steady at 1700.   The 
> scary part for me was the Left exhaust appearing to be much hotter than 
> the right.  Again I did not notice the Right side turning color as the 
> left did.  This is a STAGE I exhaust.  both sides are independent each 
> with a CAT.  I thought about the possibility of maybe a plugged CAT but 
> I'm not so sure about that.  Any thoughts of what may have caused my idle 
> to increase like that?
> Dennis


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