Got everything hooked back up, turned the engine on, and... it starts, but then immediately goes to a low, rough idle. Different from before I patched the cracked charge air pipe. If I try to put it in drive or reverse, it stalls a few seconds after I put my foot on the gas. At most I've managed to move 5 feet forward or backward in the driveway. If I disconnect the MAF sensor, idle is slightly smoother, but it stalls even quicker when I put my foot on the gas. When idling, I can put my foot on the accelerator and raise the engine's RPMs to around 3000. Double checked all air, vacuum, and electrical connections. Everything is tight.
OBDII Live Data:
- TP is reported as a constant 20%
- MAF is reported as 0.6-0.7 lb/s during smooth idle, 0.4-0.5 during rough idle, and goes up to 0.8-0.9 when pressing the accelerator
- SHRTFT is reported as 0 during idle and 30 when pressing accelerator
- LONGTFT is reported as 0
OBDII Stored Codes:
- P0121 (set immediately on startup)
Questions:
1. Is it possible the MAF sensor is bad? The readings I'm getting from it seem correct, and disconnecting it doesn't really improve things, so I'm inclined to think not.
2. Is it time to fix or replace the throttle? I'm inclined to think yes, based on the following:
a. It would seem that the throttle plate *is* rotating to allow in varying amounts of air, based on the fact that the MAF sensor reading changes as I press and release the accelerator (as far as I know, there's nothing else in the intake system that would change when I press the accelerator...).
b. The throttle position reading is reported as a constant 20%, even though it would seem the throttle is moving based on my observation in a. above.
Throttle fix/replace options:
1. (free) sensor film from precopster
2. $125.00 sensor rebuild kit: https://modulemaster.com/rebuilds/shop/ ... build-kit/
3. $344.99 XeMODeX R&R: https://www.fcpeuro.com/products/volvo- ... o-36050563
4. $392.79 Genuine Volvo rebuilt throttle: https://www.fcpeuro.com/products/volvo- ... 80-8644347
#1 is tempting but I'm concerned this may not be the only problem with my throttle. Also, I'm not confident that I possess the precision and patience required to replace just the film and not screw anything else up.
#2 may work but again I'm concerned there may be other issues with the throttle.
#3 seems to be a good option due to the level of testing and completeness of the rebuild, plus the fact that it's your original throttle so there are no software issues. On the downside you have to wait for shipping in two directions.
#4 would be nice if I could guarantee it would work with my existing software, but I don't have any way to check my software version before I purchase. Also, this still uses a contact-sensor design, so it would be susceptible to the same issues as the existing throttle, although it would probably take quite a long time for it to reach that point again.
In any case, I'm not super thrilled about having to remove/replace the throttle again. It's a pain in the butt to get at, especially out in the driveway in snowy below-freezing temperatures.
If I could give advice to someone with one of these throttles, it would be to proactively replace it or have it rebuilt *before* you have issues with it, so that you can do it on a schedule of your own choosing. Had I known it would get to this point, I would have done it this summer when I had the intake manifold out to replace the PCV system. The throttle was out of the car literally for *days* not doing anything... it could have been off enjoying some R&R at XeMODeX.
