Sharp 'grab' when taking foot off accelerator.

[Jonchilds]

When I'm driving around at low speed in car parks, I find that the car is very prone to 'bunny hopping'. This usually starts when I'm in first of second and take my foot entirely off the accelerator, but leave the clutch out.

The same thing also happens when I'm accelerating quickly and take my foot off the pedal. It is not a firm 'grab' like you'd expect from engine braking, and the best way I can describe it is like there's freeplay in the drive train.

I've just had the front engine mount replaced, and the rear one seems to be in a decent condition (from a quick feel of the rubber). Is it likely to be the rear mount, or something a little more involved?

[TekPhobia]

Check your idle speed, and dashpot if you have one. It "cushions" the throttle closing.

-Tim

[Jonchilds]

Idle speed is perhaps a little low. Its not perfectly smooth at the lights, but it is very regular.

I wouldnt think its rate at which the throttle closes, as it will start to hop even from a very light throttle, with almost no pressure on the pedal.

[TekPhobia]

Perhaps the next step then is to check the TPS. Which motor do you have?

-Tim

[Jonchilds]

4A-F/M in a '92 AE92 Hatch.

[TekPhobia]

Ohh...then it's a throttle position SWITCH. Got a service manual for the car? There's a procedure for checking the TPS.

You'll experience the EXACT same thing with a bad/missing dashpot.

-Tim

[Jonchilds]

I've got the Haynes manual for the car, and all it says is "An failure in the TPS will set a code 41. It the TPS requires diagnosis or renewal, it should be done by a dealer or service depeartment".

There's no chance that its the rear engine mount, its been covered in oil/steering fluid for a while, and the front was replaced because it had collapsed?

The TPS sounds like it could be an expensive job to get done at the mechanics...

Edit: Looking more at TPS assembly, there's both a dashpot an Throttle Position Sensor. I'll try bringing the idle up a little before I take the car anywhere.

[djwolford]

You mean that you're driving in 1st at say, 5 mph or so, with your foot on the gas, then let off and it jerks a bit? Every manual trans car that I've ever driven does it, so I'd guess it to be normal.

[REN69]

same here.. I usually call it the "you're going too slow for that gear" jerk.

[TekPhobia]

Read his post again. It's not just 1st gear. It'll happene in 2nd or quick acceleration.

It'll happen if the idle is too high, dashpot is dead/missing among other things.

-Tim

[silver04rollas]

djwolford is right about this happening in manual transmission cars. It happens even more in close-ratio gearing such as in my XRS in 1st, 2nd, 3rd and 4th. Although, it happens only in a specific range for every gear, which depends on the optimum torque point for that particular gear and it will progressively happen at a higher rpm as you move up through the close-ratio gears as the ratios drop in the higher gears ( 1st is usually around 1:3.4, 2nd is around 1:1.8, 3 is around 1: 0.9 and so on).

[cobrajet25]

Mine does this when I am going about 5-10 mph in first or second (like in a parking lot), when I have my foot just BARELY on the gas, not when I let off. It is not just a light bouncing, either, ...the car is CHUGGING like mad. I am not bogging the engine, either. I know what that feels like, and this is something different. RPMs are about 1200-1800. Sounds similar to your problem. I have a '90 sedan (4A-FE). I thought maybe it was a weak spark? It only seems to do it when the car is in gear and moving (engine under very light load). The engine runs perfectly when out of gear and the accelerator is held open the same amount. Dashpot is fine. Maybe I should check my TPS? Regards, Aaron