ive searched and searched and tried lots, but nothing has worked yet, so i wanted to tell my situation and see what kind of advice i got

i got a 94 z28, brand new rebuilt (1000 miles ish)back to stock specs pretty much with bolt ons. nothing too fancy.
what it does-it runs great when u get on it or anything over 2200 rpms. when it starts it idles at 1500 tho and slowly creeps down to about 1000 and then maybe after 30 mins itll stay idling at about 1000-i dunno if this is related but its not the main problem yet

under 2000 rpms under load the thing misses and stumbles and falls on its face. what is that?
wires r good, plugs new, i cleaned the maf today, i got a tune from pcm for less, there r no vaccuum leaks, i ran injector cleaner through it, theres no arcing anywhere.

could this be the coil or the ias?
any ideas and suggestions are extremely appreciated.

 

can this be moved to the lt1 specific tech

 

Ok.

Automatic or manual trans? That will determine what the idle speed is supposed to be. Does it run a stock tune?

 

I still have my stock tuned PCM and it does run a good bit smoother with the custom tune. It's a m6 and tuned for cai, 1.6 rr, longtubes, engine overbore, 160 tstat, and then air evap and egr delete as well as my tire siZe and gear ratio. I think that's all that's on the tune

thanks for moving this for me

 

Stock idle speed for a full warmed up engine with M6 is 800 RPM. The stock tach typically reads 100-200 RPM higher than actual engine RPM. Only way to get the true RPM is with a sanner, reading it directly from the PCM. Its normal for the PCM to elevate the idle at cold start, but 1,500 RPM is higher than any vaule in the RPM vs. coolant temp table.

Are you sure the blades are closing all the way? Do you have access to a scanner so you can observe the RPM and the idle air control (IAC) counts? Are you running a stock throttle body, or aftermarket? Have you checked for vauum leaks? Can't have high idle without excess air entering the engine.

 

Sounds like a vacuum leak. Take off the elbow at the throttle body. They are notorious for cracking right at the seam where the clamp goes. Check the iat sensor too. Make sure it is seated fully.

 

It's closed fully on the stock tb but it has a trockflow elbow and it's on there good. I have checked the iac yet so I guess that's next andtheres mo vaccum leaks. I replaced all the vaccuum hoses I could find

 

sry bout my typos earlier, the right o2 sensors throwing a code now, so obv i need to replace that this weekend, could that be the possible culprit?

 

A bad o2 sensor can cause all sorts of problems. Does the car run fine before it goes into closed loop? If it runs fine when you first start it up, and then 2-3 minutes later the symptoms start there is a chance that the o2's are to blame. How many miles are on the car? Are they the original o2's?

 

those first 2 to 3 mins the cars idling high but yeah i guess it does run fine, but i havent really tested to see about the miss within that short of starting the car. ill check tonight. ummm, 140k on the chassis, and the might be the original o2s but they might have been changed with the headers. im not 100% sure. also i only have the front ones, no rears

thanks for all the help so far i really apprecitate it

 

What is the EXACT numerical O2 sensor code? Not all codes mean the O2 sensor is faulty.

 

63. That's what the scanner said but I thought codes were 4 numbers. The wording it had said exctly. Right oxygen sensor error

 

Your 94 is OBD-I. Trouble codes are in the form DTC xx - a two digit number. Its the OBD-II trouble codes that are four digits, as in Pxxxx. Don't use the generic descriptions that come with a scanner. Use a list specifically for the LT1. Shoebox has it online:

http://shbox.com/1/Dtcs.htm

DTC 63 = Bank 2 (right) Heated Oxygen Sensor (HO2S) Circuit (open circuit)

An open circuit could be due to a faulty O2 sensor, or a faulty wire or harness connector. Swap your two O2 sensors side-to-side. If the problem stays on Bank 2 (passenger side) its faulty wiring. If the problem follows the O2 sensor to Bank 1 (driver's side = DTC 13) its a faulty sensor.