Hi Guys, I'm looking for a little help here. I have been dealing with Mark, he made me a new PROM for my 1227747 TBI computer.

I'm running a 4.3 Chevy V6 in my 40 Ford pickup and using a Painless Performance wiring harness. I have had a problem with the idle speed on this engine ever since I got it running. I'm sort of a FI newbie so bear with me.

I decided that an idle speed of 725 RPM would be about right for my engine. It felt smooth at this speed. The original idle was about 630 or so and It loaded down to about 500 in drive. The PROM I got had the idle speed set to 725. I installed the PROM and didn't really notice much of a difference in the idle speed. I hooked up an Actron scanner to the ALDL and started the truck and let it warm up. Sure enough the idle was 725 and it stayed at 725 in gear. Leaving the scanner connected, I drove the truck around a while. I was quite pleased. Later when I disconnected the scanner, the idle was about 725 in park but dropped down to around 500 again in gear.

To make a long story short, Mark had defaulted the idle speed in the diagnostic mode to 725 as well so when the scanner was hooked up, the engine ran at 725. When the engine was not in diagnostic mode, it was not under the control of the computer in drive. The engine was showing IAC counts of 15 at 725 RPM. I checked the Park/neutral switch wiring and the B-10 input to the computer was ground in park and 13.3 volts in drive just as it should be. I verified that the P/N wire did go to the B-10 terminal on the connector and that the connector pins were not bent on the ECU.

My thinking is that the ECU has taken a dump. The only other thing I'm wondering about is the AC request line. Does that have control over the idle? The AC is not yet charged so it will not run.

I don't mind buying another ECU but It would be great to really solve the problem before throwing parts at it. Any input would be appreciated.