3.6 engine braking??

[mb911]

My car has always done this since I have owned it but when the throttle plate is closed the engine does what I call engine braking (while driving of course). the engine does not die it just goes into idle mode but there is no free wheeling like I would expect it is either on or off throttle nothing in between . when on cruise control it really shows up as it is not very smooth. What should I be looking for? throttle position sensor would be my guess but ut really does not use a TPS on 964 3.6. any thoughts?

[winders]

Free wheeling? Do you have a manual transmission? If you do, what do you expect the car to do if you close the throttle? You are going to get engine braking unless you push in the clutch pedal....

Scott

[mb911]

I knew I would get some sort of smart comment on this ok so lets say I am cruising at 55mph in 5th gear and the cruise is on I go over a hill and as I need less throttle input after the hill the car feels like I am putting the brakes on so it is abrupt not like a typical tranny draging the car down it is like the engine is almost shutting down. It is not shutting down but by comparrison my buddy's 3.2 free wheels a whole bunch more then my car.

by the way not new to porsches or manual tranny's

[stlrj]

No TPS? Maybe you need to double check. Free wheeling, that you speak of, is all about the TPS signaling the DME to actuate the IAC (idle air control valve) during decel at specific rpms.

[mb911]

its not really a TPS it is 2 micro switches one for WOT and one for idle circuit which works fine from what I can tell

[Lukesportsman]

Ben:

Your not new? LOL

I can appreciate absolutely no difference in my 3.6 or 3.2 in decel mode. Something is up! That is all I can contribute sadly but to confirm your doubts. Neither feel like an MFI, but my 3.6 doesn't drag anymore than my 3.2. IAC could be a culprit as I have aftermarket EFI on a car without any IAC and that is an issue with it too: sudden rpm drops. Have contemplated adding IAC to see if it softens that. Though, I'd think your idle surge with faulty IAC would have given this away already.

[mb911]

I just looked to make sure and yes there is NO TPS just the 2 micro switches

[Chuck.H]

In your example above, does the car actually slow down to below 55mph? Maybe your cruise control module isn't very smooth?

As a second test, if you do the same thing without cruise, just take your foot off the gas do you get the same feeling that the car is slowing down too fast?

And what if you do put it in neutral for this test, does it 'coast' nice then, or do you maybe have a brake dragging?

Chuck.H
'89 TurboLookTarga, 337k miles

[LJ851]

Check that the idle switch is operating, it will cause poor drivability on/of throttle if it is not engaging or engaging at the wrong time.

[wwest]

To much slack, backlash in CC pull/push cable...??

[ant7]

Brakes binding ???

A...

[Arne2]

If I'm understanding Ben's description correctly, my 3.2 does this to an extent as well. It is most noticeable in mine when on a mild downhill stretch. I've decided that the system must shut off the fuel on overrun, probably for emissions and fuel economy. If I give any throttle at all, it picks up with a bit of a lurch. Makes driving smoothly while coasting downhill a challenge.

[mb911]

Originally Posted by Arne2

If I'm understanding Ben's description correctly, my 3.2 does this to an extent as well. It is most noticeable in mine when on a mild downhill stretch. I've decided that the system must shut off the fuel on overrun, probably for emissions and fuel economy. If I give any throttle at all, it picks up with a bit of a lurch. Makes driving smoothly while coasting downhill a challenge.

Yes You got it that is what I am experiencing and it just does not seem normal for a car built in the 90's that someone would have spent that kind of money on new I would expect it to be at least on par with a ford escort of that vintage. Some have suggested that it based of the big displacement of the engine but it has to be a something simple. I going to clean the IAC and see if that helps a bit.

[ant7]

Originally Posted by Arne2

If I'm understanding Ben's description correctly, my 3.2 does this to an extent as well. It is most noticeable in mine when on a mild downhill stretch.

I think you have hit the nail on the head there, but i must say i dont find this to be a problem with my 3.2, infact i find it an asset, but then again, i live in wales uk, where most of the hills are big ones!
However, i do appreciate that it could be an annoyance in more flat terrain.

A...

[Arne2]

Originally Posted by mb911

Yes You got it that is what I am experiencing and it just does not seem normal for a car built in the 90's that someone would have spent that kind of money on new I would expect it to be at least on par with a ford escort of that vintage. Some have suggested that it based of the big displacement of the engine but it has to be a something simple. I going to clean the IAC and see if that helps a bit.

Keep us posted on your results, please, Ben. If this behavior could be reduced, I'd be happy.

I've seen/felt this type of thing in other cars, although seldom quite this dramatic. My E36 328i did it, for example. But in the BMW, the reumption of fuel happened so gently that it was barely noticeable. You could see the effect in the fuel econ. gauge more easily than you could feel it.

FWIW, I do have a Steve Wong chip in mine (91 octane for exhaust-mods). I did not get the factory chip with the car to revert to, I'd put the stock chip in as a test if I had one.

[Tippy]

Ever since I setup the overrun fuel shutoff in my MegaSquirt system, my car engine brakes pretty significantly during coast. I don't remember the Motronic system doing this.