Isolating ETM from Throttle Pedal Issues

[boosted5cyl]

'99 Volvo S80, 215K miles, yellow badge'd ETM.

When I started the car up yesterday it refused to accelerate anything beyond 1800RPM and would misfire on cylinder 2 & 3 at idle. Eventually plugged in laptop and pulled a P0121, which seems to point at either the ETM or the pedal module? The throttle position value read in OBD was 0%, however I dont know for sure if thats reading pedal or plate, or if it stops sending a value

Right now the only reliable way I can get it to run it start the car, warm it up, pull fuses for ETM and Pedal, disconnect battery to reset ECU, hook it all back up together.

Now my second turbo is a bit leaky with oil so I may clean the ETM if its gunky. It was cleaned two years ago when I rebuilt the top end, but im not in much of a rush to replace the ETM without knowing for sure its the problem. Beyond a sweep test (I dont have VIDA/DiCE) is there anything else I can check to narrow the problem down?

[precopster]

P0121 is the front or rear potentiometer on the ETM.

A test you can perform is to cycle ignition to Pos II then listen for the ETM's cycle which is a humming noise for around 6 secs after ignition on then it switches off with a clicking noise if the engine isn't running.

The above test only confirms the ETM is getting power and the circuit board is responsive. Your ETM may be a candidate for a contactless DIY sensor swap if that's the only code you have.

You're getting 0% on throttle angle because you only have 6 seconds to test with engine off.

[boosted5cyl]

P0121 is the front or rear potentiometer on the ETM.

A test you can perform is to cycle ignition to Pos II then listen for the ETM's cycle which is a humming noise for around 6 secs after ignition on then it switches off with a clicking noise if the engine isn't running.

The above test only confirms the ETM is getting power and the circuit board is responsive. Your ETM may be a candidate for a contactless DIY sensor swap if that's the only code you have.

You're getting 0% on throttle angle because you only have 6 seconds to test with engine off.

Thanks Mike. The car starts and idles, just very roughly and will not rev very much if at all until I the little tapdance proceedure above. Then once that's done I can drive the car normally and it idles smoothly. There's a little lag in the throttle pickup point, but that may be perception too as I am looking for it.

0% throttle was with engine idling!!!

[precopster]

Looks as though it's going in to limp mode first chance it gets.

While it's driving normally do you still get 0% on throttle? Even if this is the case I wouldn't worry about this because the scanner you're running may not be reading the throttle properly. What type of scanner are you using?

[boosted5cyl]

I using an elm327 interface with whatever software launches first. Yes normally I will get a reading for throttle position without an issue with this setup.

[boosted5cyl]

So this problem only seems to happen when the car sits overnight and the car is way cold. It's been pretty cold up here lately. I have not gotten and ETS light at any point yet. Pulled the module today, date code of 03, not particularly dirty but a lot of condensation on the back of the plate.

Hoping to get a DICE over the weekend and do a sweep test.

I've read (although I can't remember where) that the need for "pairing" of the ETM to the car is misunderstood and in most cases matching the part number correctly should do the trick.
Can I just plug in a perspective ETM, do a sweep test and if it passes say I'm good?

[precopster]

There is only one other part number for naturally aspirated P2s. The rest share the same part number.

Matching programming is best done by buying one from the same model and aspiration of car regardless of part number.

[kcodyjr]

IMO, nevermind the telemetry, the relevant facts are already apparent.

It drives normally when the ECU has just been reset.

The throttle pedal itself does not have any adaptive behavior. It either works or doesn't. Thus, it works.

Thus, you might have an ETM issue, or an actual operating condition, that's triggering limp mode.

I'd expect that any actual out-of-range operating conditions that could cause misfires or limp mode would also throw specific codes, unless one or more sensors are malfunctioning, but I'd also expect that in itself to throw a specific code.

If someone has a quick checklist of sensors that can fail without the failure itself being noticed, those are worth checking first. Otherwise, if it were my wallet, I'd be ordering an ETM from Xemodex, or maybe doing that DIY sensor swap that precopster mentioned. I tend to like clean replacements, though.