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There is an LT1 at the shop that has a surging issue only when it is HOT (idling for a really long time) ... driving it around it runs flawlessly, until you sit at a light for a minute or two, and it starts to surge.
They checked for a vacumm leak, and there is none. Anyone have any other suggestions as to what it could be??

(btw, this thing is completely stock).

If you need any other info, just shout. Thanks.

 

Didn't know you were familiar with the LT1s!

Do you work in a shop or something? or is it just a buddy of yours?

I have no idea what the problem could be, but I'm a novice compared to some of the otehr guys in here lke Gangly or ChrisB

 

Have you tried cleaning out the injectors????
check the plugs, wires, etc.

 

I had a 97 TA for 2 years ... so I am decently familar with it .... not as much so as I am with the LS1's though. That is the reason I am here, I have no idea what the problem is.

Oh, and yes we did check all the plugs, wires, injectors, harnesses, etc etc. Still no clue what it is.

 

Ditto. Plus check the TPS (throttle position sensor) and O2 sensors, (but those would cause problems when cold also)

 

Yeah the car runs excellent until it gets up past the normal running temps ... meaning that it will idle fine for 10 minutes or so, or drive around perfectly normal until you sit at a light for a few minutes, or idle it for a few minutes past when it becomes hot ... then it starts to surge for no apparent reason.

I will have them check the TPS and O2 sensors monday ... any other suggestions until then?

 

The part about it running normal until hot throws me a little. Hmm... no carburetor on there? j/k LOL

Well, the Opti-crap is often the culprit when it comes to misses/erratic idle, but operating temp shouldn't play a role in that case.

What year car is it? '95 and up have vented opti's and are less susceptible to carbon tracking and moisture damage.

 

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It is a 93 i believe. No carb...

 

Check the optispark which would be your ignition its cam driven so check that and if you have a scanner to check for trouble it will also help.

 

scanned it friday, it throws no codes whatsoever

 

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Any other ideas guys???

 

i had a 96 camaro come in with a similar complaint, after driving 20 miles on the highway, the customer would get off the exit ramp, and the car would run hot at the trafficlight, then cool down a bit ashe drove, but once it got hot, it'd miss, run poorly, etc. i ended up putting a waterpump and opti-spark on it, and it was fixed. not to say this is the answer to your problem, but at least check the cooling system, and if you have a scanner, watch the spark.

 

It honestly sounds like a burnt plug wire, or a broken plug.

____________________
Rob
1994 Firehawk#319 (slightly modified)
11.83@120.61
MODLIST
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2002 Trailblazer
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"Garp bit Bonky"

 

When nothing else seems like it could be the problem, REPLACE THE OPTI

 

Normally I would agree ... but it runs flawlessly under normal conditions, which leads my away from a burnt wire or bad plug(s).

They haven't gotten a chance to put it in a bay since it has been very busy down there, but when we do and I get it scanned hopefully we will have some more info and maybe something will jump out at us.

 

When you say it's surging at idle, is it acting like the IAC valve is not adjusting the idle properly? From your description of the symptom, that could be a cause.

 

i highly doubt its the opti or 02's. My guess is simply carbon buildup in the motor. There is a foam that you can spray into the motor that will get most of the carbon build up out and that will do the trick most of the time. Many vehicles experience this issue and an LT1, being as old as they are now, start to experience it a lot. When my LT1 was torn down and rebuilt, there was TONS of carbon buildup inside the motor and on the valves. Our 2002 Yukon had the same problem(surging when it sat at idle for even a short amount of time once warm) and that took care of it immideately(sp?)and we havent had the problem since.

 

I will bet my life on this. ITs your EGR valve on the back of the intake. Im 100% sure. I had a terrible surge problem with my impala. You need the 96 F- body six-speed EGR Valve.

You problem has been solved.

 

On another board, there was a thread about hot engine surging at idle and low RPM. One of the suggestions was to replace the IAT sensor. It's about $8 at most part stores (BTW - the new part is in a brass housing, not OEM plastic, but it fits and works). This, the Seafoam (Carbon cleaning) treatment, and cleaning my Throttle Body (man that thing was filthy) cured the problem in my 94Z.

 

there is a little tiny part that controls the spark that mounts next to the coil. It actualy sits right against the head. Driver side. You need to move this off of the head and relocate it. When it starts getting hot it will malfuncion. good luck.