93 Volvo 850 engine revs high by itself

[z31jaime]

Glad to see I'm not the only one with this issue.

After searching and with the Help of ROBTHEMODD we found on Volvoforums a thread of people that had the same issue. IT turned out to be the water Temp. sensor. THE sensor tells the car its "cold" and the IACV starts to pump to warm the car and revs it to 4k rpm trying to heat the water....


Most of them said they noticed the TEMP guage in the car go dead when the Reving happens...so check that. What I did was when the car was reving @ 4k RPM I pulled the Plug for the IACV...and Bam the car dropped to normal idle. so I knew It had to do with that, and it wasnt a vac leak or anything like that. I wasn't throwing CEL because thats a normal function of the car, to warm the motor.

I pulled one for the junk yard and suddenly CEL came on for low coolent temp. and the reving went from 4k to only 2k. so I knew I was looking in the correct place. I decided to clean the contact of the sensor because it was in a junk yard and exposed and noticed that the female side of the plug (attached to cars harness) was not looking good. IT has the same rubber insulation as the Injector relay that gets brittle and causes loose contacts so I pushed the wires up and they right out of the plug so i knew it was bad. I connected each wire by itself to the sensor then slid the plastic part over it all and so far today I havent had the reving issue.

sorry its a long story but I figured the more detail the better. I tried a NEW ECU< MAF< AND IACV and it looks to have been just a plug. GOOD LUCK>

[jreidko]

Thanks for the thought z31jaime.

I have actually tried pulling the connection to the IACV and it didn't cause the revving to stop. But i hadn't tried looking at the temp gauge or the temp sensor itself. Looking for this gremlin has been such a pain since it only happens periodically. I've been compiling a list of things to try next time it does it and based on what you mentioned maybe i'll try pulling the connection to the temp sensor and see if that changes anything.

Cheers, hope to report back before it's below zero here in Chicago. - jreidko

[sariano]

Do you have any problems with your car not starting after this happens? Our 850 revs high off and on then will not start if we shut it down, wait time is 20 minutes (somewhat annoying).

[GoinFor300KMi]

jreidko - it looks to me like your Throttle Position Sensor has failed. I missed reattaching mine while putting things together after doing a PCV job. The TPS on my N/A engine is difficult to see - its underneath the throttle body and I didn't notice the plug lying loose. Anyway, when I started the engine I had accelerating idle just like you describe. My '96 has OBDII, it gave me P0120 and P0123 codes so I knew instantly what the problem was. I think the 93 is different, no OBD, but you have some kind of error codes. A new TPS costs 50 to 100 bucks and is easy to replace but it would be nice if you can verify that's what the problem is.

[jreidko]

Hey Sariano,

When my 850 does the revving it will start without a problem. You might check your main relay, it's mounted right above the radiator under the lip of the plastic cover that sits across the front of the engine compartment behind the hood latch.

I had a problem where my car would randomly die and then wouldn't start for 5/10/15 minutes and replacing the main relay and the fuel pump relay was what fixed it.

-jreidko

[jreidko]

Hey GoinFor300KMi, i'm not getting any engine codes, but i will take a look and verify that the TPS sensor is hooked up properly. On the 93' 850 it's OBD-I where you can pull codes by watching a blinking red LED in the engine compartment.

Cheers - Jreidko

[jreidko]

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]

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?

[kcodyjr]

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.

[polskamafia mjl]

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.