My 94 runs good most of the time. Slightly rough idle though. The big problem is that when you run the A/C in town and the fan cycles, sometimes the engine misses. Idle is not affected. Pulls of fine if you stay below about 1/4 thottle. If you mash it any harder it misses real bad and pings. If you dont let it get to 227' or above with the A/C on it does not act up. Turn the engine off and start it later and its fine. Any ideas?

 

Is it pinging... ? High temperatures can cause the fuel to pre-ignite (aka detonation).

 

Red94: So basically as long as the temps are under 227 you have no problems (and you only see 227 with the AC on)? My first guess would be the coil - if you haven't upgraded this. Up to 95 the LT1's came with very poor coils. Any of the aftermarket unit's will be fine.
The other issue would be knock problems as was mentioned above. You might try running some 100+ octane in there and see if that helps. If so then you probably just have a good bit of carbon deposition in the heads/pistons. You could try using "GM Top Engine Cleaner" (available from the dealer) to clean this out.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:[/color]<HR><font face="Verdana, Arial" size="2">pre-ignite (aka detonation). [/color][/QUOTE]

Not to be picky but those are two different things . Pre-ignition is when your a/f charge lights off before the spark plug fires - this is normally cause by hot spots in the chamber (from carbon buildup, sharp points, etc.) and can be exacerbated by hot running conditions.
Detonation is an explosion as opposed to controlled burn of the charge. This can happen before the spark, after the spark, before TDC, after tdc, etc. Pre ignition can lead to detonation, but detonation can occur without it (pre-ignition).

 

First thing I'd do is get a lower temp switch.Then id check my injectors for leaks.
The o-rings may be worn.
The hotter it gets the more likely they are to leak.

 

Red94Lt1, my polo94Lt1 had the same type of stumble. most noted when the engine was hot and ac on. once i notice the car stumbling i go buy some octane boost, i like NOS brand raceing formula, $10 will do 17 gallons (a tank full). This always made it run better. (sometimes you get bad gas) over the last few months I have changed the fuel filter, pluggs, wires, coil, also added an adjustable fuel pressure regulator to boost fuel pressure. haven't noticed any stumbles since the wires and coil. I'm not sure which to suggest to you but my car sure feels good these days. last time i went to the track i had slower et and faster trap time, tires were spinning with power i had not noticed befor

 

I'm having a similar problem. You said you changed the ignition coil, did you just replace it with a new GM coil or an aftermarket one? If aftermarket which one did you get?
Thanks,

 

new coil was a MSD High Energy, if you want exact modle number email me and i get it for you. BTW coil change is a bit tricky - the coil is riveted to the coil module, you drill out the rivets and reuse the module.