Have difficulty moving throttle off-idle without stalling the engine. Unless done very slowly, the engine seems to starve of fuel and sputters out.

Another, perhaps related, problem - At highway speeds if I engage the cruise control at 60MPH (for example) it seems that when the control system applies
a small bit of throttle to maintain the set speed, nothing really happens and the car continues to slow - then the control system decides to apply "big" throttle to get back to the the set speed resulting in a very surging kind of ride.

I'm thinking either the idle set screw adjustment on the throttle body, or perhaps the air mass meter is slow to respond.

Any and all ideas appreciated!

Charlie

 

The cruise problem sounds like a vacuum leak to me. As for the other throttle issue, it is likely that you have a MAF problem. Disconnect it and see what happens (post back). There should be an idle control switch that change the engine speed control once you press the gas pedal.

 

I'm trying to get this problem fixed, so that I can give the car to my daughter and son-in-law, The problem still is that when coming off of idle the engine stalls out. The only way to keep this from happening is to finesse the move off of idle, ever so slowly. This, of course, doesn't work well in traffic.

I looked at the output signal from the MAF (~0.2 idle, rising to over 1.0 volts with throttle) While doing that experiment and moving the throttle by hand from under the hood, I could hear an audible gasp when the throttle plate was opened. That has me wondering if the idle control valve may be involved. When I remove that connection, things seem to improve slightly.
I cleaned the valve, it moves freely, and believe I hear it humming along when connected, but I'm not 100% on that.

I'm wondering about the "idle switch" that you mentioned in your last post. Where is such a thing located on the B6304?

 

I'm not sure. I just delivered my 960 to my daughter in college and took her S70 because it was missing and I need to take care of that for her. I dealt with this with a 740 GLE several years ago so I'm just guessing. But with the car OFF, you should hear the click when you move the throttle by hand. It came from a switch that was part of the throttle body. I belive it switched the car from "throttle cable" controlled to "idle-electronic controlled". There is a good chance that you have a major vacuum leak, like disconnected line or your Idle Control Valve is bad.

 

Unlike my 240s -- the TPS on the S90 (Bosch 0 280 122 001) is switchless and clickless - just a potentiometer. So it's hard for me to figure how the ECU establishes the "idle position" after a TPS replacement which I did early on in this project. I was hoping there was some sort of ECU sequence to reset (e.g. key on to ignition position, wait for 30 seconds, ....) but can find nothing in the service manual or here on the forums.

I can find no vacuum leaks and, at idle, the vacuum gauge shows a good strong and stable level.

What effect does the throttle stop adjustment (screw/nut) on the throttle body have on the transition from the off-idle condition? Is there an adjustment procedure for that?

 

I apologize but it's above my head. Look extra close for vacuum leaks, all elbows. You have a great dealership there, University Volvo. You may give the car to the kids and tell them to have University take a peak at it. You have no CEL codes?