850 T5 hard starting when warm

[nferi93]

Hi all,

I know that there are already topics with this issue, but I'm starting to go crazy as nothing seems to fix this.

Here's the situation: my 850 T5 has issues with starting, after engine reached operating temperature. It cranks, but it will fire up only after like 15-20 seconds of cranking (on hot engine). When I start it in the morning, it starts easily 90% of the times, but if leave it for 3-4 hours, and it has still difficulties. I got DTC's, but usually one at a time: 231 (only after highway driving) and 233. If I delete them, they return only after weeks. Once I got 121, but it hasn't returned since then. Otherwise it drives good, but when the engine is cold, the idle is fluctuating a little bit: drops to like 700 rpm, but soon it will return to normal. Instead when warmed up, and just when coming to a stop at a light, the idle will be around 1100 for a few seconds, then drop to normal.
I noticed, that it starts easier when i disconnect the TPS (no matter if I try with the old or the new one).

What I've done:
-replaced coolant temperature sensor with new OEM
-replaced air and fuel filter
-replaced throttle position sensor (new Bosch)
-replaced plugs, cap, rotor (both Bosch)
-tried with 2 replacement crank and cam position sensors, IAC valve
-tried unplugging EVAP valve on radiator, and blocking the ports
-checked for vacuum leaks 10 times, but found nothing
-I pulled the fuel rail to check if injectors are leaking, but all were dry
-Replaced fuel pressure regulator, fuel pump, fuel pump relay

It is a manual, so it doesn't have a kick down sensor, neither the one that prevents an automatic starting in drive.
I now suspect the MAF sensor, but when I tried to start with the MAF disconnected, it made no difference. I also measure it with a multimeter, but it seems good, according to volvo service manuals.

My questions are: What else could be causing this? Could it be the MAF even if it drives fine, and no matter that it wasn't better when disconnected? Or what could the disconnected TPS mean?

I really appreciate your help, as I'm trying to figure this out for a year now, and it is now really annoying.

Thank you and regards,
Feri

[shaker_chi]

Hello Feri,

Based on your description, I would be willing to be you have a vacuum leak. What method have you been using in your attempt to find them? The most common would be using carb cleaner. Don't forget to spray around the intake manifold and throttle body. The leak may be coming from somewhere besides a hose. As much work as you have done trying to solve the problem I would try to find an indy shop to do a smoke test. I paid $50 the last time I had one done. Have you looked at the cam position sensor? If yours is original, you may want to swap it out because it is going to go eventually. I've had 2 go bad on me both at around 175,000 miles. Try pulling the MAF sensor and giving it a good cleaning with MAF sensor cleaner. You can pick it up at your local autozone/Napa.

[nferi93]

Hello,

Thank you for the advice. I inspected the hoses visually, and on suspected locations I tried the carb cleaner method. Unfortunately I couldn't find any shop doing leak test here. By the way I checked some videos on youtube and I'll try to do a smoke test myself with a homemade "smoke machine", but it will not pressurize the hoses, so it may not reveal the leak.
I already replaced the cam position sensor, and cleaned the MAF, but it didn't solve the problem.

This weekend I took a look at CBV membrane, and found that it has two holes on it. But I guess its not a classic vacuum leak, as it is not unmeasured air so it should not affect the air-fuel ratio. I plan on replacing that, but I need to wait for the part to arrive.
But what do you think, could this cause the hard starting anyways?

Thanks,
Feri

[abscate]

I don't think a hole in the CBV will cause a hard start. There is no boost at start, so the CBV will be holding closed by the spring

[darrylrobert]

mine is doing the same thing only on hot 30c summer days after a drive, except no engine codes. mine has been since buying the car 4 years ago, did you solve this problem??