93 Volvo 850 engine revs high by itself

jreidko · Post by **jreidko** » 02 Feb 2012, 09:29

Hello, it's been one and a half years, but i thought i would make a final entry here for anyone else looking at this thread.

Unfortunate news: I never did find a fix for this issue, since the problem started it's been a 100% checking/observing, so no new parts or modifications were done relating to this behavior.

Good news: The dang problem stopped, haven't had it happen in over a year.

Sorry there wasn't something definitive here for folks. Car had been running great for about a year, but now has started to give me some trouble again, i'm off to the other forums!

oldebondo · Post by **oldebondo** » 29 Sep 2016, 08:32

Hello Folks, I thought I'd try to revive this thread as I am having a similar problem on my '97 Volvo 850 T-5, 215,000 miles. Here are some facts:

- Starting is fine
- After driving 25 minutes at highway speed and coming to a stop, idle will "hunt" intermittently from normal to ~1200 RPM. I have been putting the AT in Neutral at these stops.
- I have cleaned the IAC twice and checked for cracked hoses.
- I have sprayed WD-40 on several vacuum hoses while idling to see if I could find a leak (especially the one on the passenger side under the Intake Manifold.
- I have checked the DC voltage on the Throttle Position Sensor and found .55 at idle to 4.5 at WOT which appears correct.
- I have cleaned the Mass Flow Sensor with MFS Cleaner.

I can't seem to find the culprit. Any suggestions?

Post by **kcodyjr** » 29 Sep 2016, 11:05

Will WD-40 do it? I use carb cleaner or starting fluid for that. Also, try it after the 25 minute highway drive when everything's hot.

MAF cleaner, according to some, is in the same category as "blinker fluid". I for one have never gotten a result from it.

Post by **polskamafia mjl** » 29 Sep 2016, 17:33

If you just have a hunting idle that isn't quite the same as OP's problem. I would recommend unplugging the MAF and see if the problem continues. As mentioned, cleaning the MAF will do little to nothing.

oldebondo · Post by **oldebondo** » 03 Oct 2016, 08:01

I unplugged the MAF sensor and the engine RPM increased slightly. Plugged it back in and the RPM dropped back to the original RPM. So what does this mean?

Post by **kcodyjr** » 03 Oct 2016, 08:11

As yours is a 93 and they're a very different animal, wait for someone to confirm.

If you unplugged the MAF and it didn't stall immediately, it sounds like it wasn't really using the MAF. I'd suspect bad MAF.

oldebondo · Post by **oldebondo** » 03 Oct 2016, 08:48

oldebondo wrote:Hello Folks, I thought I'd try to revive this thread as I am having a similar problem on my '97 Volvo 850 T-5, 215,000 miles. Here are some facts:

- Starting is fine
- After driving 25 minutes at highway speed and coming to a stop, idle will "hunt" intermittently from normal to ~1200 RPM. I have been putting the AT in Neutral at these stops.
- I have cleaned the IAC twice and checked for cracked hoses.
- I have sprayed WD-40 on several vacuum hoses while idling to see if I could find a leak (especially the one on the passenger side under the Intake Manifold.
- I have checked the DC voltage on the Throttle Position Sensor and found .55 at idle to 4.5 at WOT which appears correct.
- I have cleaned the Mass Flow Sensor with MFS Cleaner.
I can't seem to find the culprit. Any suggestions?

Thank you kcodyjr for your prompt reply! Actually I hijacked this thread and submitted my problem which I thought was similar. Mine is a 97 850 T-5 wagon with 215,000 miles.

Post by **abscate** » 03 Oct 2016, 18:06

Don't plug and unplug electronics while they are hot. Turn car off, remove key, unplug, then restart.

When you unplug the MAF the car runs on a preset injection scheme based on rpm. It will run pretty well on this. I drove from Boston to NY this way recently when I blew a turbo hose

93 Volvo 850 engine revs high by itself

Re: 93 Volvo 850 engine revs high by itself