Haibeck PROM Idle

[gbmidyear66]

I have been trying to uderstand why I can't get my engine to idle below 800 RPM. I bought an AutoXray and I now understand why.

The desired Idle is indicating 750 RPM. I had always understood desired idle was 650 RPM. I have a Haibeck Prom (scanner ID is 2457) - there is no indication on Marc's site that he boosted the Idle speed.

What are others with the Haibeck PROM getting?

My TPS and IAC are good, so looks like I don't have a vacuum leak.

[Paul Workman]

With the factory chip and now with Marc's chip, my idle (as seen on the scanner too) has always been around 700 to 750 (closer to 750), depending on engine temp, air temp, etc. I don't recall reading that 650 is the "desired" idle speed, to be honest - I seem to recall somewhere that 700 "ish" is fine. To my ear, when near the tail pipes, @ 750 it seems to be very "happy" (smooth, not stumbling, plugs look good too). :thumbsup:

Is there a particular problem with the idle speed other than not being down around 650? I mean 1000 or 1200 would be another matter, but 750 seems about right (IMO) to keep the plugs clean in traffic (my carburetor days talking here:rolleyes:).

BTW, my tach appears to have about the same error as yours. I ran my rpm up and down and recorded the scanner reading and the tach readings and found my tach to read pretty close to 15% high - "...a common error related to the electrolytic "filter" capacitors in the tach circuit drying out." (I read that somewhere...makes sense to me).

FWIW,

P.

[tomtom72]

I just bought a PROM from Marc and it has not changed my idle speed that I notice. I was around 700 /750 and sometimes it would be around 650/ 700 using my scanner to read it, not the dash tach.

My scanner's software says that the "Desired" idle speed is supposed to be 650, I think. I hardly ever see that on the Tach, it sometimes looks like it's close when the scanner says the idle speed is like 700 to 750....I guess what I'm saying is that it seems that the scanner does a better job of reading the idle speed than the dash board tach does. Most of the time my dash board tach stays between the 500 and 1k mark, almost dead in the middle between those two marks and floats up & down.

Also, I would add that the scanner's readings when they do fluctuate, they do it at about one second intervals. I always figured it was okay as long as the motor ran smooth and the tach was close to agreeing with the scanner. I mean how accurate can our tachs be? I think it's okay what you are seeing for a tach indicated idle speed. What does the scanner say?

:cheers:
Tom

[Aurora40]

Do you see IAC counts higher than 0 at idle? I believe my desired idle is generally 650rpm. Maybe that's something Marc has changed recently, you might just ask him.

[secondchance]

I am running Marc's chip also. My idle varies between 650 to 750 depending on how she feels on a particular day.

[gbmidyear66]

Aurora, My IAC count at start in open loop mode is 24, and then drops down to about 10 when warm and in closed loop. I understand 10 is a good number.

OK - looks like now I need to change my sig. Opened up the ECM and found to my suprise - a DRM prom (not the Haibeck prom the previous owner claimed). I didn't pull it but it has a red checkered flag with a "1" in it.

It has skip shift, and fans come on early, But I am not thrilled about the idle speed. There is nothing on their site about the features of this PROM, anyone have the specs on this? Anyone have a current Haibeck prom hanging around they want to unload?

[Aurora40]

Yup, sounds like there is plenty of overhead for the IAC to bring the idle down. So that is good.

Maybe a previous owner raised the idle in anticipation of an aluminum flywheel?

[SharkPilot]

Maybe a previous owner raised the idle in anticipation of an aluminum flywheel?

Dumb question time...

Why does the idle speed need to be higher if running an aluminum flywheel?

Thanks, Jim.

[tomtom72]

I think a bump in idle speed quiets the rocks in a can noise that the trans will make with a non-DM flywheel set up....I stress "I think" that is the accepted thinking on the matter.
:cheers:

[Aurora40]

Yup, I believe the idle tends to be smoother if you raise it a hundred or two, which would help the SM noise.

[Kevin]

I think a bump in idle speed quiets the rocks in a can noise that the trans will make with a non-DM flywheel set up....I stress "I think" that is the accepted thinking on the matter.
:cheers:

this sounds right to me too

[Dandy97]

I think a bump in idle speed quiets the rocks in a can noise that the trans will make with a non-DM flywheel set up....I stress "I think" that is the accepted thinking on the matter.
:cheers:

I have an aluminum flywheel and a Haibeck chip with the idle bumped up to 900. Yes, it is for that very reason, it lowers the gear rattle caused by the lightweight flywheel.