Volvo 850 1996 / Tranmission or PNP or what? Topic is solved

[erikv11]

You should not unplug the MAF while the car is idling, that could be bad for the ECU. From your description it sounds like the MAF is working: if the MAF was bed the car would run the same with it and without it.

Check inside the cap for condensation or oil. Oil and moisture can get into the cap if a rear cam seal is leaking. Also check the contacts on the inside of the cap for excessive wear and deposits, and check the metal contact surface on the rotor for the same thing.

IAC valve I do not know how to test. I do know they can often benefit from cleaning, they get dirty and get sticky. To clean the IAC valve you must remove it from the car, spray in some carburetor cleaner, shake it up to remove the gummy deposits, and then drain out the dirty carburetor cleaner. It is important to wear eye protection so it doesn't splash into your eyes. Let it dry before you reinstall it.

Spark plugs: check them for wear, check the gap is it not too wide? If you car is non-turbo the gap should be about 0.029 inches (sorry I do not know the mm equivalent). Are the ceramics around the electrodes discolored like black or sooty? Normal plugs should be a tan color there.

[abscate]

0.75 mm for those plug gaps, but you should be using the multi prong plugs on a NA motor, which you don’t gap.

A fresh cap , rotor , and plugs is a basic Stage zero start on a poor running Car, about 100EU in parts

The only explanation I can think of for your D stall problem is a sticky torque converter solenoid that isn’t releasing the TC in Drive fully. Overfilling the ATF could contribute to that so put that right

[BeerDeer]

0.75 mm for those plug gaps, but you should be using the multi prong plugs on a NA motor, which you don’t gap.

A fresh cap , rotor , and plugs is a basic Stage zero start on a poor running Car, about 100EU in parts

The only explanation I can think of for your D stall problem is a sticky torque converter solenoid that isn’t releasing the TC in Drive fully. Overfilling the ATF could contribute to that so put that right

The car isn't stalling now, it's just idling roughly. When I rev it, it doesn't do it.

[DennisCA]

Try cleaning the IAC first. Then you can look at the plugs, distributor cap and rotor. You can get Volvo OE plugs, rotor, distributor cap from Motonet.

Also look at your leads, they should have a date on them.

[BeerDeer]

You should not unplug the MAF while the car is idling, that could be bad for the ECU. From your description it sounds like the MAF is working: if the MAF was bed the car would run the same with it and without it.

Check inside the cap for condensation or oil. Oil and moisture can get into the cap if a rear cam seal is leaking. Also check the contacts on the inside of the cap for excessive wear and deposits, and check the metal contact surface on the rotor for the same thing.

IAC valve I do not know how to test. I do know they can often benefit from cleaning, they get dirty and get sticky. To clean the IAC valve you must remove it from the car, spray in some carburetor cleaner, shake it up to remove the gummy deposits, and then drain out the dirty carburetor cleaner. It is important to wear eye protection so it doesn't splash into your eyes. Let it dry before you reinstall it.

Spark plugs: check them for wear, check the gap is it not too wide? If you car is non-turbo the gap should be about 0.029 inches (sorry I do not know the mm equivalent). Are the ceramics around the electrodes discolored like black or sooty? Normal plugs should be a tan color there.

I just removed the MAF while the car was operational, and the engine immediately stopped with a hard shutoff. If I try to start it without the component, I have to rev the engine to keep it running; otherwise, it dies due to low RPM.

I’ve also noticed condensation inside the oil cap and dipstick, which I believe is caused by the clogged PCV system. I’m currently waiting for the replacement kit to arrive so I can address this issue.

In the meantime, I’ve picked up MAF cleaner to clean the MAF sensor and carb cleaner to clean the Idle Air Control Valve (IACV).

I’m planning to check the spark plugs as well. From what I can tell, the spark plugs, rotor, and cap are about 5 years old (maintenance book). The spark plugs are NGK.

I’m not sure how to check the gap on the spark plugs. Could someone explain what the gap means and how to measure it? I’ll do my best to inspect the plugs and replace them if necessary.

Thank you for your advice and guidance!

[BeerDeer]

0.75 mm for those plug gaps, but you should be using the multi prong plugs on a NA motor, which you don’t gap.

A fresh cap , rotor , and plugs is a basic Stage zero start on a poor running Car, about 100EU in parts

The only explanation I can think of for your D stall problem is a sticky torque converter solenoid that isn’t releasing the TC in Drive fully. Overfilling the ATF could contribute to that so put that right

I’ll be checking everything and updating you all shortly. Based on what I’ve read in the service book, the spark plugs, rotor, and cap appear to be about 5 years old.

Thank you for your patience and support—I’ll share more details soon!

[BeerDeer]

Try cleaning the IAC first. Then you can look at the plugs, distributor cap and rotor. You can get Volvo OE plugs, rotor, distributor cap from Motonet.

Also look at your leads, they should have a date on them.

Thank you for your help. I have an update! The transmission stalling issue seems to be resolved. The transmission fluid was overfilled, so we’ll need to drain some of it. My question is: Can I disconnect the tube connected to the radiator for the transmission fluid to drain it slightly? Or should I use the plug to drain it instead? I’ve also heard mixed opinions about performing a power flush cleaning on older transmissions. Some say it can cause more issues, so I’m hesitant to go that route. The overfilled fluid has been like this for about a year with no noticeable problems until now, but it’s likely best to fix it properly.

The car has been parked for the past few days. When I started it recently, it ran fine—no rough idling, no smoke, and it drove without any issues. However, after stopping and restarting the car, things changed suddenly: the idle became erratic, more exhaust smoke (with an "uncooked" smoke appearance) was noticeable, and the car started stalling while driving.

I’m wondering if this is related to the fuel pump or fuel pump relay—could an intermittent issue with fuel delivery be causing this? Or perhaps a faulty sensor (e.g., MAF, oxygen sensor, or crankshaft position sensor) that is not consistently failing? I tried using both iCarSoft and ANCEL AD310 code readers, but neither was able to connect or retrieve error codes. There are also no dashboard warning lights or error indicators showing. The lambda light disappeared after disconnecting the battery, and there’s no check engine light at the moment.

Additionally, I checked the oil level, which is okay, and the radiator oil shows no loss, so the head gasket seems fine. How can I read diagnostic codes for this issue if the readers aren’t connecting? Is there a better tool or method to use? Also, why would the car behave fine on the first start but develop these issues after restarting? This situation is puzzling, and I’d appreciate any advice or suggestions you may have. I’ll try starting the car again soon and will update you on any changes. Thank you so much for your help!

[DennisCA]

I have the VeePeak OBDCheck BLE+ Plus reader, it works with the "850 OBD-II" app and allows me to read and clear error codes.

I don't really know anything about automatic transmissions myself, I only ever buy manuals.

The lambda lamp is just a Check Engine Light, it lighting it up doesn't mean there's a problem with the O2 sensor.

I would still clean the IAC first, then check the ignition components.

[Clemens]

I'd drain all the ATF with the drain plug and refill with fresh ATF (ATF 320, I believe). That way you have the first drain and refill session done which is considered standard maintanance to most of us here.
I think you need to refill 3.7 Liters after the drain, and always measure with the engine running.

[Clemens]

Also: Don't do a power flush. Only drain and refill. It's the safe way.