Car jolts when pressing or releasing the gas pedal.

jeffsws · Post by **jeffsws** » 20 Jun 2019, 08:22

Hey all,

My manual ’96 850 2.0 T5 (Italian model) will jolt every time I press or release the gas pedal. No matter the speed or gear. The link below shows this (Ignore the check engine light – I removed the idle air control valve connector to test.) In the video It might be a bit hard to notice when I gas but releasing the gas should be noticeable.

https://1drv.ms/v/s!AkNcPQgBxT-pgYAN7Thkd-aqPm-fPQ

I’ve tried the following to solve the problem:

Replaced (and later cleaned) the idle air control valve with a known working one.
Replaced (and later cleaned) the throttle position sensor with a known working one (throttle bay is also very clean)
Installed a new throttle cable and adjusted it accordingly.
Cleaned MAF sensor.
New air, cabin, oil filter (with oil change)
Checked with vacuum leaks spraying some carb cleaner but noticed no alteration when the car was idling.
Replaced injectors with some white ones I had spare.
Replaced 3 engine mounts – passenger, clutch and upper one.
Wires, distribution cap, rotor and plugs all changed last year.
PCV serviced last year
I replaced the coolant hoses and most of the vacuum coming out of the turbo.
Put back the original 4.3 ECU (currently using a 4.4 one)
New front struts and springs and sway bar end links.
New rear shocks and springs.

Everything is volvo original or OEM. Nothing has helped. In fact, I believe it has made zero difference.

I also have a manual ’97 850 2.5 NA and a manual ’98 v70 2.5 Turbo. These cars drive as smooth as butter in comparison.

Has anyone experienced such an issue? It’s driving me nuts.

Post by **Eddystone** » 20 Jun 2019, 11:34

Can't tell much from the video.

Check engine mounts and control arms first.

If it "jolts" to the side as in changing direction, consider the control arms.

Also consider engine mounts if it's fore and aft.

If the engine is actually surging and changing RPMs, it would be in engine management as you suspect.

jeffsws · Post by **jeffsws** » 20 Jun 2019, 11:51

Did you have sound on when watching the video? You can somewhat hear it when I release the pedal - but yeah, the video isn't the best. And no, the rpms don't change.

The three standard mounts have been changed but only the top one actually needed it; I only replaced the other two to see if he helped. I looked at the two big hydraulic mounts and they aren't leaking, but other than that I've no idea if they are bad or not.

I'll check the control arms but I'm almost certain the car does not jolt to the side.

WhatAmIDoing · Post by **WhatAmIDoing** » 20 Jun 2019, 22:10

With a single mass fly wheel, a small jolt is to be expected as you switch between the transmission turning the engine and the engine turning the transmission and vice versa (if that makes sense). The jolt occurs due to the transfer of energy and momentum (or a bunch of other physics terms I don't understand). Dual mass flywheels were designed to remove this shock and make riding in a manual trans vehicle more comfortable (aka boring). An excessively worn clutch, bad axle / driveshaft, bad motor mounts, and bad suspension will make the jolt MUCH more noticeable.