fast.asleep

I finished my head/cam swap and am waiting for my mail order chip so to get the car running I left the stock chip in. The car idles at about 200 rpm and dies quickly but when I scanned it with my Autoxray it reported that the desired idle speed was 3187 rpm on the stock chip!!

(When it was stock the car idle at 700 rpm.)

What's going on?

DanielRicany

If I recall from one of my cars it displayed the same thing. The target idle on the scan tool is not accurate.

What probably needs to happen in order for you to idle correctly is that you need more fuel. If you can get it to idle long enough to get into closed loop, you may be able to see it idle properly.

bjankuski

Check it when it is running, it will not show 3187 when running.

Cliff Harris

Because of limitations in the ECM microcontroller (8-bit processor), the smallest RPM increment that it can handle is 25 RPM. If the number you're seeing is not a multiple of 25 RPM then it is bogus.

LT1_383

I think for desired idle RPM the multiplier is sometimes 12.5. I think with LT1 not running it might report 3187. 255*12.5=3187.5. 255 is the highest number for 1 byte. After it starts, I think it goes down to a more reasonable number.

Cliff Harris

You are correct. My mistake. I was going by memory, which isn't the most accurate way...

fast.asleep

Yup. When it's running the desired idle reading drops to 1000rpm. It's a mute point now anyway since I have an appt with the dyno tuner tomorrow morning

Thanks for everyone's help