Candleman

Hey guys, I have a symptom and want to find the cause. When in gear at low RPM (1000-2000 or so) and maintaining a slow speed with very slight but constant pressure on the gas the car lurches as if I were rhythmically pumping the gas peddle. This is not apparent when accelerating or when cruising above 2000RPM or so, but that doesn't mean it's not still there. I'm going to check the spark plugs of course but I doubt that is the cause. Can you think of what might be causing this problem? F.P.R.? M.A.F. sensor? I'm not sure when this started, I don't remember feeling this when I test drove it or on the drive home from Miami, but I may not have noticed it because rarely am I trying to drive a steady 5 to 15 mph, and that's pretty much the only time it is noticeable. Has anyone here experienced this? What course of action should I take?

Thanks, Ryan

AO

Drive it faster!

Lizard928

there is nothing that you can do to fix this imo.

I have standalone management and cant fully dial it out. Imo it has to do with the injector sizing/control.

Avoid letting this happen though as it is not good on the bottom end. Just keep the rpms higher.

Mrmerlin

I would check the throttle cables including the the one that opens the throttle plate under the MAF so you will need to remove the aircleaner to do this, make sure the throttle is closing all the way listen for the click in the TPS whan you open the throttle on the side of the intake it should happen just as the throttle plate moves, check for a bit of slack in the foot to throttle junction as well the cable might be too tight

FBIII

Lean surge?

jon928se

My theory is that it is a combination being at a very light throttle opening ie sometimes throttle is open and some times it is shut causing the brains to keep switching between the idle map (using the ISV to control airflow) and the part throttle map.

Combined with around 1200rpm coasting in gear (approx can't remember) is where with the closed throttle siwtch engaged the brains switch from no fuel at all back to the idle map.

Changing relatively rapidly between these three scenarios as happens at crawling traffic speeds as you alternately accelerate a tiny bit then coast means the 'puters can't keep up hence the "surging"

Ispeed

The torque tube drive shaft is twisting and it is giving the car a brain fart as it tries to maintain an idle, no big deal at all. Just don't drive that slow.

Candleman

5-speeds don't have TT's do they?

soupcan

What gear are you in when this happens? All have Torque Tube, Autos have Torque Converters.

Ispeed

This only happens with the 5 speed. Seems to be a normal thing, the low speed lurch.

RyanPerrella

why do you poke along at 1000 rpm?

toofast928

Check the engine coolant sensor for being out of spec. After that MAF sensor is next on the list.

heinrich

common issue. answer is keeping revs higher. also common in 944 for very different reasons.

Charley B

Why is everyone avoiding the obvious here? This can only be a symptom of vacumous interuptis, caused by a cracked block.

heinrich

In the 944, the issue is a result of the differential between the (downward) point where the ECU can effectively regulate mixture as the throttle closes, and the (upward) point where the idle stabilizer starts taking effect. To mitigate, there is a throttle cam made by Weltmeister which accelerates the opening of the throttle (progressively).