Hey all,
I have a wonderful S70 with about 130,xxx. Over the past couple of years I've had sporadic idle RPM's and increasing acceleration problems from my car. The initial symptoms were that the car idle would jump around 1000 +/- 200 RPM's when coming to a stop. Once stopped it would settle down at normal 1000 rpms. Sometimes now as I come to a stop or even if I just let off the throttle and it has to idle down it'll dip really low to about 500 rpm's, hover there as I slow down, and then come up to 1000 rpm's when I stop.
When I floor the car or have the pedal around 3/4's throttle (trying to pass someone, for instance) the car will accelerate but with many hesitations. It won't linearly accelerate, it'll stumble up in increasing RPM's. Sometimes if I apply throttle slowly it'll accelerate more fluidly. This problem is sporadic though, so it doesn't always do it.
The hesitation problems also begin to occur more frequently if I've driven the car several hours on the highway. Sometimes cruise control will disengage and I can't use it until I turn the car off and back on again.

I find that all the problems happen less when the car is cold.

I suspect Air Mass Meter (AMM) issues. I've also read info about the TCM failing. I have no lights on in the car though. A few years ago when these problems began I cleaned the AMM and everything improved. That lasted about a year and the problems began again. Fuel economy seems to be where it should be.

I look forward to any help y'all can offer. Thank you.
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The AMM can only be cleaned once and be effective, save up for a new one.

If your car still has the white labled TCM, it may be disintegrating. Most of the yellow tagged TCMs last much longer.

I would suggest you also clean the throttle body, as you should be idling at about 850 rpm and not 1000rpm. And start checking for vacuum leaks at all of the elbows, replacing cracked and loose hoses. A poor vacuum will result in higher idle as well as fouled spark plugs.

The cruise control might be turning off because of a 'pending' code which gets cleared after restart.

Thanks for responding, Klaus.

Seems I overestimated the idle. It's idling right around 850 rpms when warm and just above 1000 when it's cold (for the first 30 seconds after turning the car on).

I do have the white labeled TCM so I'll start setting some money aside for that. As I understand it there's a light that'll come on the dash when that unit fails? Also, what does TCM stand for? Transmission/Transaxle/Throttle Control Module?

Is there an easy way for me to figure out whether the AMM is failing or the TCM?

You da man, Klaus!

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Throttle Control Module or Electronic Throttle Module, take your pick.

Yes, there will be an engine code when the throttle fails. The normal tell-tale is a fluctuating idle. And it is not cheap to fix:

http://www.xemodex.com/technologyimproved/product/electronic-throttle-module-etm-repair-return/

You could first try to clean the module. You know, get all of the carbon off the butterfly valve. Just make sure that you plug it in firmly when done.

The AMM or MAF may also create an error code.

A vacuum leak will not create an error code, but it will make your engine run rough and burn rich.

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My back feels better when I sit in a Volvo seat