Volvo S70 '99 Cruise control surging / pulsating, headache!

[precopster]

I can assure you the dealer/or factory adds the cruise function to the DIM on P80s. I think the software is probably pre-loaded in the ECM which has to do all the speed and throttle angle calculations however the OFF/ON switch for the option is contained in the DIM.

On autos the speed is calculated from 2 speed sensors on the auto. It may pay to check the wiring to the ABS wheel sensors but I think in your case an outdated ECM version may be the issue. I drove a P80 2000 V70 Denso auto for 100,000kms over about 4 or 5 years and the cruise function was super accurate. It held really well on upgrades, especially so when I manually changed gear.

My P80's Canbus was upgraded early during my ownership so I can't say what it was like before upgrade.

[Pater]

I can assure you the dealer/or factory adds the cruise function to the DIM on P80s. I think the software is probably pre-loaded in the ECM which has to do all the speed and throttle angle calculations however the OFF/ON switch for the option is contained in the DIM.

On autos the speed is calculated from 2 speed sensors on the auto. It may pay to check the wiring to the ABS wheel sensors but I think in your case an outdated ECM version may be the issue. I drove a P80 2000 V70 Denso auto for 100,000kms over about 4 or 5 years and the cruise function was super accurate. It held really well on upgrades, especially so when I manually changed gear.

My P80's Canbus was upgraded early during my ownership so I can't say what it was like before upgrade.

Thanks for your help so far Precopster, very useful to get feedback from a fellow '99-'00 Denso (ex)driver.
What was the reason to upgrade the canbus (CDM) in your case? Maintenance?
Just to be clear, the ECM is not outdated, but the CDM (DIM/Instrument cluster/whatever name) is. The rest of the modules are all up-to-date.

It makes sense that the calculation should be performed by the ECM, as it is in control of the ETM. I agree that the ABS speed signal might be faulty which causes the ECM to overact with a nervous cruise control as a result.

I'll check the wirings and connectors of the ABS sensors. The two front reluctor rings have been replaced. Any idea how to check the ABS sensor output? I do know the output should be 7mA and 14mA (low/high signal). VIDA only lets me read the vehicle speed, not the raw output of the sensors. Is there a way to check this without an oscilloscope?

[Reinie]

I had the same issue with my 99 S70. The problem was a broken reluctor ring. I noticed you replaced them but might be worth checking again.

[precopster]

I upgraded the Canbus to help with transmission shifts. Also for the Oz and Brit markets we had neutral stop software in the TCM (which wasn't implemented until the P2 in the USA)

I recently had to change out a coil pack on my 2001 T5. Once I did this th e surging stopped. I had surging and acceleration if I pressed the cruise set button (+ or -) whilst accelerating.

[Pater]

I had the same issue with my 99 S70. The problem was a broken reluctor ring. I noticed you replaced them but might be worth checking again.

Great you solved your problem, well done. Did you had an unstable speedometer (speed signal) with this broken reluctor ring?

[Quozie]

Hi guys,
This has been an interesting read.
My S70 is doing the same,

• pulsates when not loaded.

• 50-60ks

• 80-100ks

• park w/ revs held 3000+

• cruise control doesn't need to be on for issue to reveal itself

Replaced coils, plugs & cleaned MAF sensor and throttle throat.

Only difference is, (other posts say after market) I have a black and a white tube entering the rear of air box. White one runs to front of the motor the black one, not attached anywhere, cam't for the life of me find where it goes.
I've read that it attaches to front of air box, can't see anywhere.
So my question is, does anyone have a photo/s of it's location & could thus be a possible cause?

Thank in advance.

[abscate]

The black and white hoses are the vacuum hoses for the air temperature door on the air cleaner. One end connects to the intake manifold, the other goes down under the air cleaner snout to the vacuum motor. It is not visible from up top, you have to use a mirror to see it.

[Quozie]

Sweet, thank you heaps, that's a little clearer, will check it out this afternoon