I swapped a 355 with afr heads ,first tpi and comp cam 265xfi and I can't get it to idle. The fuel pressure is set at 45 and I have played with the timing and still backfires thru throttle body and then dies. It seems to be running good till it idles down. Any ides? Also while I was playing with the timing the computer threw a **** load of codes.

what size injectors are you using and what has been done for memcal reprograming ?

24lb injectors and purchased a pcm for less chip from a member off this site and installed that but made no difference.

What are your iac counts and do you know what sice injectors the PCM for less I assume piggyback is set for ?

iac was 150-160 I changed the iac with another one I had laying around but again it made no difference. Pcm for less chip is a piggy back and it was programmed for 24lb injectors.

The iac count at 150-160 was at cold start or after the engine was warmed up or over 150F ?

I tried running it with and without the pcm for less chip but still made no difference with the popping and idle.

both it 150-160 cold and warm

it started blowing black smoke and threw a bunch of codes while I was turning the dizzy so I gave up for today.

It sounds like a vacuum leak or maybe the ecm is not controlling the iac. The suddenly running rich could be the ecm going into lhm.
Some ECM'S may have differant wire colors. Check your wiring diagram. Letters A B C D will be on IAC. A B will show but have to remove plastic clip holding wire pins in to see C D.

Blue wire white stripe to A on IAC connector.
Blue wire black stripe to B on IAC connector.
Green wire white stripe to C on IAC connector.
Green wire black stripe to D on IAC connector.

Use a jumper wire to cross A and B on ALDL diagnostic port!

Then use an OHM meter and check between A and B? Should be greater than 20 OHMS. Check OHMS between C and D should be greater than 20 OHMS? If not replace IAC.

Diagnostic procedure says to use test light and all termianls should light... but I do not have one other than 12 volt. They are refering to a test light that will light for any voltage. So I used a DMM (Digatal Multi Meter).

Testing wires from harness to IAC connector.
A should be about .5 volts.
B should be about 12 volts or batterey voltage
C should be about 12 volts or batterey voltage.
D should be about .5 volts.

If not check wires are connected to proper pin at ECM. Then check wire for break by connecting ohm meter to each end of wire for continuity. If all wires are OK and all wires are connected to proper pins on ECM? Replace ECM.

this test was provided bye user EagleMark

what should the iac read when cold?

Blowing black smoke = WAY WAY WAY WAY WAY too much fuel.

Start there: back off the fuel pressure and see if it gets better.

Change out the spark plugs before the test. They're almost certainly toast.

If the minimum idle speed is set correctly, no vacuum leaks , correct timing the iac will be commanded in off ect reading and will be between 15-30 counts.

would the iac cause the popping ?

No.

Start here.

Don't outsmart yourself over something THAT simple. Start with the eeeeeeeeezy and the obvious.

Change the spark plugs out. Being fouled, a symptom of too much fuel, is probably the cause of the popping.

See my signature for a logical technique that may help keep you out of the weeds.

thanks for the info