96 850T uncommanded Revving MVSolved bad ECT

Post by **j-dawg** » 12 Apr 2015, 18:54

Check for vacuum leaks? I'm having a similar problem, though not as bad. Popped a P0171 the other day.

socalover · Post by **socalover** » 12 Apr 2015, 20:32

Funny you say that about vacuum lines. There are 3 that are rotting. Just found by my neighbor.

Post by **erikv11** » 13 Apr 2015, 00:14

If the cable and linkage and the throttle body are in good shape, and vacuum lines are not, that is a very good bet. It's not the MAF.

kaneelschep · Post by **kaneelschep** » 13 Apr 2015, 00:47

Vacuum just makes it idle nasty and can hold the gas a bit AFTER pushing it. Not suddenly rev it to 4000.
Maf does not do this. Simple to test. Just unhook the cables.
GasCable or linkage will only hold the gas. not push it. Unless its allready stuck. Then it will always push the gas.
Swap the temp sensor

https://www.matthewsvolvosite.com/forums ... 2&start=14

Post by **misha** » 13 Apr 2015, 08:07

socalover wrote:Well... It did it again this morning. Revved up to 3000 rpm while in park. So when my friend opens shop tomorrow he will be hearing from me. As far as the maf it hasn't been replaced since I've owned the car for 5 yrs and the code pointed to it. Ugh

I told you.Bad maf have specific symptoms and ALWAYS the same symptoms for every of these cars.
Check the codes...maybe there are some pending ones and replace those vacuum lines.They can make all kind of problems,but your problem acts like it's mechanical.Check that throttle cable for sticking.

Ask for your money back for a BAD and PAYED wrong diagnosis.

kaneelschep · Post by **kaneelschep** » 13 Apr 2015, 10:30

I really dont understand why you keep pointing to the throttle cable.
A throttle cable can get stuck shortly or permanently because of all kind of things.
Lack of lubricant or a kink or a piece of thread came loose, the mounting came loose, etc.
But in all cases this will only HOLD the gas for a certain amount of time AFTER you pushed it once. And it could hold it on 2000 or 5000rpm or whatever.
But it can never ever just suddenly rev the engine by itself.

A bad maf won't rev the car either. You can drive without a maf even. it will just use more fuel and/or run a bit rough.
Just try it to see. It costs nothing and you will know for sure.
Unhook the electrical plug and drive till your problem happens again.

Swap the temperature sensor and your problem will be gone.
It costs nothing compared to a new maf or checking and replacing all the vacuum lines.
I spent 30 euro on a new one from the dealer.

socalover · Post by **socalover** » 13 Apr 2015, 13:25

When I look up temp sensor it gives me options for different types (not brands). Which one am I looking for? Thank you.

Post by **erikv11** » 13 Apr 2015, 13:32

Generally good points but I disagree about the vacuum lines: replacing any (even all) bad vacuum lines is cheaper than a new ECT sensor and will save you a lot of trouble. It is basic maintenance, especially as old as these cars are. May or may not be the issue here, but should be looked at right away. Just use generic rubber vacuum lines from any auto parts store.

Post by **erikv11** » 13 Apr 2015, 13:37

Lots of info in here about the ECT, the one for your car is the same as the one for a 98, cheapo aftermarket ones are hit and miss:

https://www.matthewsvolvosite.com/forums ... =1&t=52203

I'm not convinced it is the ECT but that is a decent bet. I would check the resistance of the one you have in there (see the link) and check the ECT connections.

Post by **Ben850** » 13 Apr 2015, 15:26

socalover wrote:How about the Baro sensor?

No "Baro" Sensor till '98, with the new ECU.

They call it a MAF sensor at that point, although it is not even measuring the induction system. It is on the fender to open air.