Hopefully I'm in the right spot. I have a 94 z28 with a fresh built 383 stroker. I had it tuned by TPIS. The problem I'm having is while driving in any gear under 2000 RPM, it will be very sluggish and backfire through the intake. As soon as I put it in a lower gear and the RPMs go over 2000, it goes away. It idles perfect. It's like there is a deadspot in the throttle. It has a 58mm throttle body. The IAC counts are around 15 at idle. RPM at idle is 1000. TPS is at .59 at idle. While idling, if I give the throttle a quick tap, it will backfire also. Makes it hard coming off stop signs. I basically have to have the rpms over 2000 before letting off the clutch.

 

Have you ever pulled any codes? How old is your opti and have you ever checked the rotor screws?

 

There are no codes. The opti had the cap and rotor replaced by the engine builder about 4 months ago.

 

has the new 383 always had this problem...or is this new?

IAC at idle is low at 15....but don't think that is the issue on flat spot/backfire

idle 1000 rpm???...that's high.....you sure you don't have a vacuum lean?

The TPS is close enough

what is your fuel pressure?

 

I haven't been able to check fuel pressure yet. It has acted like this since installed. TPIS set the idle that high. They also drilled the holes bigger on the TPS sensor to get better idle. I did the cheap way to check for vacuum leaks and sprayed starter fluid on all vacuum lines but no change. It also has 30# injectors and 340lph pump.

 

Could be timing related, vacuum leak or both.

 

could be a combination of issues...maybe tune....maybe FP

Sounds like they drilled the TB slightly to big to get it to idle right. Fine line on that. each 1/64" makes quite a difference. Ideally IAC wants to be 30-35 (32) at idle at operating temp

1k rpm idle...you have a big *** cam?

From this side of the keyboard sounds more tune related. IDK anything about TPIS as a tuner

I would invest in a FP gauge. One that has a hose on it so you can tape it to the windshield to monitor, especially when you have your mid throttle issues, to see if fuel pressure is within spec to rule it in/out as a possible issue.