98 V70 struggles to get out of idle when cold

[Goupil]

I'm having a weird issue with my 98 V70 B5254T, it's struggling to rev out of idle when cold (ECU in open loop mode). Once past idle it will rev fine, it's just the getting from idle to reving where it falls on its face and almost stalls (first few seconds of the video)



It happened after unplugging the battery for unrelated work (seat controls), does it every time the engine is cold.
When it gets warm enough to go into closed loop the issue disappears.

- Tried replacing the MAF, TPS and IAC with no change.
- Coolant temps, ambiant temp and vacuum are all reporting coherent values to the obd
- It's not the first time i've unplugged the battery and it has never done this, so i think it's more than a fuel trim needing to relearn.
- Car is tuned by VAST and runs on E85, but it used to run fine so can't see why the map would suddenly be wrong
- If it only happens in open loop, it cant be an issue with the O2 sensors right

I'm running out of ideas about what components could fail just enough to be an issue only when cold

[scot850]

You don't mention the coolant sensor (ECT). Have you checked that and it's connections at the connector behind the power steering pump?

Cold temp running issues are to me normally the ECT or air/vacuum leaks that can be more of an issue when cold.

Neil.

[Goupil]

the ECT value on the odb works, I guess that if i'm seeing it that means the ECU is getting the data as well ? Tested the sensor resistance and it was 3300ohms for ~20°C/68°F

Can't find my spare one so I might have to order a new one just to be sure

Gonna get the smoke machine out tomorrow, just in case a vacuum hose somehow gave up the day I do unrelated work on the car

[scot850]

I seldom find that happens. It is a case of, if it worked before I worked on the car, and not afterwards, then I did something in the process!

Neil.

[Goupil]

Found my spare ECT, makes no difference.

I'm reading conflicting information on the interwebs: the vacuum at idle should be 16-20, but is that in PSI or inHg ?

[jreed]

From the 16-20 values given for idle vacuum, I would say that the units are in inHg ("inches of mercury").