Help: 850r with a mind of its own

swedishmeatball88 · Post by **swedishmeatball88** » 24 Sep 2012, 08:48

Hi.

I've had an 850r for about a year now. The car has given me no trouble, except a month after I initially got it, the car started to stall out on the way to work if the engine rpms droped to 1500 or below. I made it home by constantly revving the engine and after looking it up on this site, determined the MAF needed to be replaced and the the car was good as new. This morning, the car was fine, and after driving for 20 minutes, I was on an off-ramp, with my foot on the brake, and the car lurched forward, almost hitting the car ahead of me. The car was at 2000-2500 rpms and the oil temp gauge was at zero. Once the car started moving again, it calmed down and the oil gauge went back to normal. Then 15 minutes later, it did it again except this time the car sustained the higher revs for a while, actually until I stopped the car.

From looking online, it seems like this is either a MAF issue, which I 've dealt with before, so maybe there's some other issue with that I overlooked? or its a coolant thermostat issue?

Thanks.

Post by **JDS60R** » 24 Sep 2012, 09:08

Oil temp gauge ? Does your car have an aftermarket oil temp gauge?

I would start with the throttle body to make sure its clean and not sticking. Then pull the codes from the car.
If the car lurched on its own (without a sticking throttle plate)I would suspect the trans. What color is the fluid in the trans and when was it last replaced?

swedishmeatball88 · Post by **swedishmeatball88** » 24 Sep 2012, 09:23

yikes, i've clearly illustrated my lack of knowledge, haha. In the cluster with the turbo gauge and the gas gauge, the one to the left of the gas gauge, "oil pressure gauge"? That one dropped. I'm going to clean the throttle body when I get home.

Thanks for your help!

byeboy · Post by **byeboy** » 24 Sep 2012, 10:16

Does yours look like mine?

Post by **JDS60R** » 24 Sep 2012, 10:21

I think he means coolant temp gauge to the right of the fuel gauge.

I would look at the cooling system first as a Volvo will take all sorts of punishment - but not overheating.
Please
Check coolant level, test ECT sensor, inspect, test and/or replace thermostat and if all that fails - test the coolant for combustion gasses. Also - replace the pressure cap (often). I am always shocked at how soon those caps fail. I order them by the box now.

swedishmeatball88 · Post by **swedishmeatball88** » 24 Sep 2012, 12:40

That's the one, the coolant temp gauge. Also, I had the heat on this morning which was the first time It'd been on in months. There is no CEL on so could I have Autozone check for codes or would nothing come back?

Post by **JDS60R** » 24 Sep 2012, 13:42

I would check out the coolant issue before driving the car again.

swedishmeatball88 · Post by **swedishmeatball88** » 25 Sep 2012, 19:17

so I checked all the parts of the coolant system and it seemed fine, and the car was running fine. I cleaned the throttle body and it seemed like I fixed it. Then, driving home today, I got a CEL, though the car still drove fine. Went to autozone and the code is po133, so should I replace the o2 sensor, or is it something else. And if its the o2 sensor, what sensor should I get, Denso, Bosch, or some other company; I'd like to get an oem one.

Thanks.

Post by **JimBee** » 25 Sep 2012, 20:05

The rpm surge is what I'm focusing on. What malfunctions can trigger a double shot of fuel into the engine?

Could the MAF? It sends a signal to the ECU to increase fuel based on how much air is coming through to the intake manifold. But before the incoming air is increased to boost the MAF signal, the throttle position sensor has to send its signal to the ECU that more fuel will be needed to match the increased air that's on its way. Although if the MAF were faulting, it could send a false signal about air.
Is you new MAF a Bosch or brand X? I've posted about how to live test your MAF using a multi-meter. That's not hard to do and worth the effort.

The O2 sensor monitors the oxygen level downstream of combustion, feeding that data back to the ECU (I think as a check on air-fuel mix), but that would come after rpm increase—if working properly. Hmmm.

I would remove the TPS and bench test it with a multimeter. You can clip leads onto a ground pin and output pin (I've forgotten which are which, but you'll find them by trial and error—there are only 3 pins).

The TPS is a variable rheostat, probably takes 12 v. in on one of the pins, then I think varies between 1 and 5 v. out. But you'll just be testing it for smooth increase-decrease in resistance.
It's my understanding the TPS's don't go bad often, but testing it you'll see if when you slowly turn it from one extreme to the other if the rise or fall in resistance is smooth and consistent. If the resistance jumps around on your workbench you can assume it will under electrical load, giving faulty info about fuel demand to the ECU.

Post by **boosted5cyl** » 25 Sep 2012, 20:39

Interesting one. I wonder if you are looking at a possible intermittent electrical issue? An O2 sensor issue would not cause the car to lurch forward under any circumstances but an electrical issue might as the idle is controlled electrically via the IAC valve. Might be worth removing and cleaning the IAC valve, checking your electrical connections
At this particular point I would not bother replacing the O2 sensor. Its not likely to be the root cause of the issues you describe.
Could be as simple as a hanging throttle cable as well. So inspect cable and spring condition, movement of the system is smooth. If it happens again where the RPMs are pegged around 2000ish, put your foot under the gas pedal and lift it up a tad to see if it makes a difference.