Big flat spot at low RPM?

[Dan in NZ]

Tall gearing for highway economy doesn't help either...

If it takes 1-2 seconds to respond, and you haven't let out the clutch, I would suspect something is wrong....

[pundit]

Hi all! I let my Father in law drive my E34 today. He was complaining about a big "flat spot" on take off. To be honest the car has always been like that, ie, I have to "wind it up" a bit to get it to move, I thought it was just a bit of latency. I thought this was normal but he says it's not. Any ideas on what could cause this? It's an M20B20 engine.

Thanks,

Shaun

As others have mentioned, for a 2 litre motor in a car the weight of an E34?...you're right.... it's normal!

[Bill R.]

flat spot and a lack of power due to displacement... You can have a small motor without a flat spot and you'll feel it trying to go it just won't have the power, a flat spot is a definitely delay when you give it gas before you feel it do anything...I would first check for cracks in the rubber boot between the afm and the throttle body and any other vacum leaks, then check all the usual , plugs, cap and rotor, valve clearance, and then check temp sensors, and i would also check the CO settings at idle which will have a big effect on flatspots or hesitation... CO will require some with a exhaust gas analyzer to measure it for you...

Hi all! I let my Father in law drive my E34 today. He was complaining about a big "flat spot" on take off. To be honest the car has always been like that, ie, I have to "wind it up" a bit to get it to move, I thought it was just a bit of latency. I thought this was normal but he says it's not. Any ideas on what could cause this? It's an M20B20 engine.

Thanks,

Shaun

[E34-520iSE]

a flat spot is a definitely delay when you give it gas before you feel it do anything...I would first check for cracks in the rubber boot between the afm and the throttle body and any other vacum leaks, then check all the usual , plugs, cap and rotor, valve clearance, and then check temp sensors, and i would also check the CO settings at idle which will have a big effect on flatspots or hesitation... CO will require some with a exhaust gas analyzer to measure it for you...

Bill your description is excellent! I have, without doubt, got a delay when I put my foot on the throttle - it feels like nothing is going to happen (or the engine could die), then revs up. I guess the idle CO is adjusted at the AFM. If this was not set up, would that explain the rich mixture (smelly!) at idle? Any chance you could explain how the AFM flap works?

Thanks again,

Shaun

[Lennyz525i]

Another really simple thing to check and adjust would be the throttle cable. I had some slack in mine, it actually made a nice difference when I tightened it a bit.

[Interceptor]

Another really simple thing to check and adjust would be the throttle cable. I had some slack in mine, it actually made a nice difference when I tightened it a bit.

BMW recommends 1 mm slack for optimal results.

[Lennyz525i]

There was still some slack, I just made very minor adjustments. I suppose the cable linkage loosens a little over time.

[romus]

maybe your throttle "wire" is a little loose? If you step on the accel. pedal and engine responds with a delay i think that might be it. Check out the throttle cable/wire near the inlet manifold and twist to tighten it. Try to do this is a quiet place and put your ear close to listen for the throttle position sensor "click". Leave it at JUST under that click. Test it by pulling lightly on that wire and listening for the click sound. If you've twisted the cable over this position, your idle will run high.

I hope it's this simple thing.