1999 C70 Mis-fire type symptom at low RPM

[Kazthebassman]

1999 C70 turbo cabriolet automatic has a mis-fire type symptom, at low RPM(idle).

After warming up for a while, my engine developes what seems like a misfire. The engine stumbles, shakes and the idle drops about 200 RPMs.
It does not stall. If I bring the RPMs up to about 1500 RPMs, it seems to smooth out. It seems to run fine until you slow down. There is perceptible no power loss.
Stop and go traffic makes me cringe, hearing and feeling the stumble constantly. It does it in, or out of gear.
Occassionaly if throttle punched on highway, it may bog, as if over-boosted, but that is not consistant.
Spark plugs and coil packs have been replaced. I did the combustion gas test of the coolant and it was negative for combustion gases. Also it seems i loose my cruise control once it has started this 'misfiring'.
Any suggestions would be appreciated. MAF, MAP have been replaced prior with used ones. I was having over-boost issues prior.
Other recent prior repairs are New Radiator,nice used intercooler(from a 2004 I believe) Vaccum lines.
Oil is synth replaced every 3K. Good suction at oil fill cap.

[Kazthebassman]

Also, There are no CELs lit. I was in an hour and a half of stop and go 3 feet traffic, still no lights.

[Kazthebassman]

No one ? I'm digging through the engine, i see I have not replaced all the vacuum hoses. They all look good. I'm thinking maybe the cam position sensor ? I don't know. Any thoughts or testing procedures ?

[Multiskilled]

Sounds like early stages of etm failure. Take it off and clean it

[Kazthebassman]

Thanks Muliskilled. Yes, it does seem a bit like early ETM failure, but not quite like everyone else's description of symptoms for failing ETM . I'm thinking ETM or maybe an injector now.
The odd thing is it does it only when fully warmed up and only at idle.
I am the 3rd owner. This car has been owned in Philadelphia, NYC and now me in NJ. Lots of idling in traffic probably. Hopefully not the TPS as well. I may try an ETM cleaning next weekend.
I have an independent Volvo specialist nearby. Do you think it may be beneficial to have them read the vehicle with Vida/Vadis or what ever they use ?

Also, while the engine was doing this, I removed, then reinserted the coil pack connectors, on each cylinder. There was no perceptible change other than when I removed the connector from cylinder # 4 or #5. Very strange. If cylinders 1 through 3 aren't firing then how is it not stalling, while presumably, running on just cylinder 4 and 5?

[mayorpeoria]

I replaced an ETM several years ago on my '99 V70, after it was all back together, I found out it was a broken wire powering the ETM. It didn't have problems like you are describing here, but I thought I would throw this out. Wish you luck, you are skilled in the process of elimination by the steps you have explained, some would have 6 new parts replaced by now and still have the problem.

[Multiskilled]

I had the same symptoms as you , took off etm and cleaned it thoughly with carb cleaner and replaced gasket. It's totally transformed the car .
Allow yourself plenty of time though it's no picnic getting the etm off

[Kazthebassman]

Did any of you pull the fan/shroud assembly to access the ETM ? ..or did you get it out from the side? I know there's a good bit of information about it on this site and others. It looks as if it may be much easier with the fan out.

[abscate]

If you aren't getting running changes pulling coils get that squared away first. Search for the coil resistance thread which shows the pin outs and check for voltages at the coils. They fire by individual grounding to through the ECM on these cars

[Multiskilled]

When I done mine I left the fan in but took the manifold off as I done my pcv at the same time