96 850T uncommanded Revving MVSolved bad ECT

Post by **misha** » 13 Apr 2015, 16:07

Ben850 wrote:...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.

No...they call it MAP sensor(manifold absolute pressure).Even it isn't really a MAP sensor people like to call it like that.Real part name is Barometric sensor.Map have totaly different function and it was used where MAF isn't.

socalover · Post by **socalover** » 13 Apr 2015, 18:09

Lots of good info here. Thank you all. As far as the MAF, I now know that wasn't the issue. He will be refunding me some money on that one.

So as of now the three vacuum hoses that were bad have been replaced. I just got home and started the car and it went through it's normal warm up process by idling up to about 1200 rpm and then goes down to about 900 rpm. After a few minutes when the temp needle was to it's normal spot it did go up some to about 1000 to 1100 rpm. I still think this is too high but as you all can tell I'm no expert, just trying to learn. This is all in park. I shifted into reverse and it dropped. I'm not sure 100% if that will fix the issue as it's intermittent.

I'm looking at starting with the least amount of $$$ first. So what's next? ECT Sensor or throttle body? I'm guessing not the IAC since I've been told that would make the car stall?

Post by **erikv11** » 13 Apr 2015, 18:38

Next for me would be, in order:

1 Clean the IAC (free, probably needed anyway, good bet with the description from your most recent post. It is one of the first things I do every time I get another Volvo).
2 Clean the throttle body (also free, also likely dirty anyway).
3 Check the ECT resistance and connector (also free but a little more hassle and if the ECT is in fact fine, then it is better to just leave it alone).

Also keep eyeballing the vacuum lines in case you come across another one in bad shape.

Post by **misha** » 13 Apr 2015, 18:57

...and after you finish all of that erikv11 advised you to,reset ecu by removing battery cable for 15-30 minutes.It will clear the codes and reset fuel trims.

socalover · Post by **socalover** » 13 Apr 2015, 19:16

Hmmm..... I have no codes at the moment. My trustworthy (cough, cough) mechanic cleared them when he changed the MAF.

socalover · Post by **socalover** » 13 Apr 2015, 19:45

Okay I'm going to get the three things done.

Just wanted to share the vacuum lines that were replaced.

socalover · Post by **socalover** » 13 Apr 2015, 19:51

Also when he sprayed cleaner here it made the idle climb.

Post by **Ben850** » 14 Apr 2015, 05:58

misha wrote:
Ben850 wrote:...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.
No...they call it MAP sensor(manifold absolute pressure).Even it isn't really a MAP sensor people like to call it like that.Real part name is Barometric sensor.Map have totaly different function and it was used where MAF isn't.

Sorry, I meant MAP, I could go back and edit it but I've been called out. That is exactly what I was saying , Misha.

After I had altered the throttle plate on my N/A I did not spread the retaining screws holding the plate. About a month later they had loosened, allowing the plate to move around. It would sometimes stick at a high idle, and I would have to burp the throttle to get it into place.

I had figured it out, and that is settled.

Post by **cn90** » 14 Apr 2015, 07:00

As others already said it...

1. Check and replace all suspect vacuum hoses.

2. The throttle cable: around 1998 to early 2000 is the transition year for switching from classic throttle to TBW (throttle by wire) for many car mfg's.
For Volvo S70, 1998 was the last year that used classic throttle cable. Mine went bad at 130K. So check and double-check your cable. If in doubt, replace it, it is cheap at dealer. This cable could be life-and-death issue!!! What if the cable is stuck at 4000 rpm and you can't stop the car!!!

Anyway, just an advice on safety issue...

PS:
- Bad ECT sensor ---> usually Aux Fan (in front of radiator) runs all the time
- Bad MAF ---> stumbling rpm etc.
- None of these, as far as I know, will cause sudden rev of the rpm.
The only item I know that can cause sudden rev is the stuck cable in the classic throttle body design.

Post by **misha** » 14 Apr 2015, 08:30

socalover wrote:Also when he sprayed cleaner here it made the idle climb.

Where "here"?
Btw,you found a problem or at least one of them.