Cannot cruise at 1200 rpm

[Patrick G]

This is very frustrating. I have been working on tuning my car for months and I still have one nagging problem. My car will not hold a steady cruise between 1000-1200 rpm. It will accelerate smoothly in that range and it will decel smoothly in that range, but at a steady cruise (like going through a school zone or parking lot), the car will buck and shake.

Here's what I've done to try to eliminate this problem.
MAF-less speed density tune.
Base running airflows correct at various temps.
IAC Effective area modified to allow Dynamic Air and Idle Air to match from 0-100 IAC counts.
Spark tables from idle and main tables match at lower rpm levels and loads.
Increased spark timing (32 degrees) for improved idle and low speed driveability.
Throttle cracker trimmed.

OK, here's what I think the problem is: When cruising at 1000-1200 rpm, there seems to be a conflict between the IAC motor and the PCM. I'm sure I'm getting some nasty reversion from my cam at this low rpm level, so that doesn't help either. But at a steady 4-7% TPS, the motor absolutely will not hold steady at this rpm.

Is there a way to limit the IAC from trying to correct above a certain rpm or vehicle speed? Setting the throttle follower and throttle cracker to 0 does not help.
FWIW, I am new an EFI Live newbie, but an HP Tuners veteran

[BowlingSS]

I get the same thing but around 1200 to 1600 with 0% TP. I have tried all the things you have except cracker. I increased the timing (35+) and it helped some but I still have the bucking.

Bill

[TAQuickness]

You ever find a solution to this Pat?

I'm not in a state to work on my tuning, but before the tear down I fattened up the AFR in that range and it made a positive difference. I don't recall what AFR I was running but it was in the 13.x range.

I believe the fundamental problem is the reversion that you are rapidly switching between a lean/rich condition. You can fatten up a bit before you end up in a stoich/pig rich condition, but you will still have the bucking due to the reversion.

The only real world solution I've found is to put it in first and drive 15mph thru school zone's. It scares the hell out of everybody (straight pipes ) but it's a smooth ride.

[Dirk Diggler]

Yeah i have the same issue around that rpm also but in 6th drives me nuts LOL

[TAQuickness]

Yeah i have the same issue around that rpm also but in 6th drives me nuts LOL

Want me to come fix that for you?


what gears are you running again?

[Dirk Diggler]

I am running 4.33's

[TAQuickness]

I am running 4.33's

damn... seems like with that much gear you should be able to ride thru the bucking.

[foff667]

sounds like its time to step up to that taller tire & 4.56's lol

[TAQuickness]

I spoke with Pat about this... Said he had to modify the setting for the IAC as it was conflicting with his cruising plans. I'll post my findings on this when I get the bird back online