I have an 85 Z28 305 TPI. Goodies include a BBK fuel pressure regulator set @46 PSI, Holley 52mm throttle body, Accel 19lb/hr injectors, world products 1.94 intake/1,50 exhaust 305 heads, edelbrock headers, and a summit TPI cam. When I start the engine after it has warmed up, the idle shoots up to around 1800-2000 rpms for about 30 seconds. The TPS is new and set correctly. The IAC And O2 sensor are also new. There are no vaccum leaks to my knowledge. The only part that has not been replaced is the egr valve. Could this be my problem? I am sure the upgrades have nothing to do with this because this occured when the engine was bone stock as well. Please help!

 

I'll bump your post, I think Vader mentioned awhile back about an upgraded PROM for the '85's for something similar to your problem.

I don't think your EGR is the cause.

 

Wondering if my MAF could be the problem. I have not replaced it in the 5 years I haved owned the car. I have 3 ECU'c and 3 MAF burnoff modules from othe 85 tpi cars, but my car idles like crap on all three.

 

One of the ECU's was removed from an 85 IROC. I am currently running this one in the car. I has a hypertech stage one chip and it ran the IROC wonderfully. My car runs just as crappy on this ECU as it does the other 2 that I have.

 

Lower your fuel pressure back to 39# and see if that doesn't take care of things. It's been a few years since I had a 305 in my car but it ran perfectly on the IROC chip. In fact it ran so close to the ADS Superchip that I gave the superchip away when I swapped to a 350, and kept the factory chip in case I ever went back to a 305. (BTW, the ADS '85 350 chips stink!) Both chips were way better than the stock 85 Z28 chip!!!!!

When you raised your fuel pressure above stock, you effectively changed your injector size. The '85 (870) computer is very slow and it takes a while to change things. By putting your fuel pressure back to stock, which was 39# for that year model, you should take care of your problem.

Be sure to pull the underhood fuse for about a minute to reset the computer back to original specs. I would also run the IROC chip for a while. If you are running a K&N filter, be sure to spray the MAF with some electrical contact cleaner about a week after you re-oil it......

 

I have tried lowering my fuel pressure before, and it didn't help at all. I lowered it to 40 psi, 35 psi, and even 30 psi. I have also tried replacing the fuel pressure diaphram, but this too did no good.