1996 850R revving on its own
 

Has anyone ever heard of this? My daughter has the car at college now. She has had the car die on her occassionally since 1 1/2 years ago. I have done several things to try and stop the dying over the last year and a half and for the most part in the last two weeks it has. Last year I changed the throttle position sensor, fuel filter, plugs, air filter, checked all vacuum hoses carefully and the most recent is two weeks ago I changed the fuel pump relay and adjusted the slack out of the throttle cable. However that is not my big problem now.

Now the car will be at Idle with no one in it and it will rev up in like 2 seconds to 4000 RPM run there for a few more seconds and then it might go down to about 2000 RPM then maybe back to normal. The most dangerous thing is it has done it while she has been driving it. It does it with the new or old fuel pump relay and I also put more slack back in the throttle cable. It is still acting up and seems to be after it gets hot and not while it is cold.

What is going on to cause this? What should I check? I feel it is unrelated to anything I have done in the past but not sure. I am a frequent reader of the forum and have never seen anything like this posted.

Please help.....

I could have sworn I was registered on here already, but here goes.

I have a similar problem, mine over revs at slow speed, fine at higher motorway speeds.

It could be a few things matey, poss vehicle speed sensor is defective or the throttle sensor too. easy to change but might be an idea to test them first if you can.

I failed to mention that throttle position sensor was changed to a new one last year. Specifically is there anything else to try or test? And if so how would I test for it.

this could be caused by either a bad temp. sensor or thermostat.not uncommon...seen alot of these posts on here

My 850 R is doing the same thing man. I'm about positive it's the temp. sensor as nonsense619 said cause every time mine does it the temp will go from normal running temp. back down to cold. Does it take it a few times to start sometimes?

I have never heard of something like this...

its because when the engine i cold the revs go up to warm it up quicker.. a bad ect will say its cold (when its not) and the revs go up.

I haven't noticed the temperature gauge fluxuating before. She told me about what it was doing at idle (about it revving up) and I went there to check it myself a few days ago. She also told me it was kind of hard to start like stumbling around like it wouldn't take off and idle correctly.
When I did look at it and start it for the 1st time, it did stumble at start. After idling and cutting the car off and then back on over the next several minutes it started back each time normal. After about 10-15 minutes of idling I was standing next to the car then I witnessed it myself. Almost at once the engine revved up to 4,000 PM and held there while I was turning the throttle where the cable attaches up and down to try and get it to slow down and this didn't help. Finally after about 10 seconds is dropped to about 2,000 RPM then a few more seconds back to normal idle. So it was completely warmed up when it did it.
I couldn't get it to rev up while driving it for 1 hour a few days ago but since then and as of today she says that it is either revving up while driving also now or is just shuts off. It is doing both of these things now. She is able to get it restarted each time that it quits however both of these conditions are serious safety issues.
Also the check engine light was not on the other day as of today is still not on.

Do you still think the temperature sensor is a good idea to still replace? Does anyone please have any other ideas on what the possiblities are?

Thanks in advance for your help.

I just replaced mine and it cleared up the normal idle - 4000rpm and it stopped it from running really rich but now the car will still idle kinda funny and even though the car's cold, the temp gauge will move up to running temperature like three seconds after it starts. Not sure what could cause this. That and the cooling fan still blows after i shut it off and i gotta unplug the battery to get it to stop.

She did confirm the temperature gauge was going all the way to cold when it revved up. So I will try the temperature sensor and thermostat and keep you posted.

Thanks

Got the car yesterday and it was revving before I could get to the gas station in two minutes. Check engine light was on before too. So after gassing it up I pulled the codes and it was PO117 (temperature sending curcuit low). Last night I replaced the temperature sending unit and thermostat and reset the codes. So far not it is not revving today and the CEL is not on. I will keep you posted.

Sounds like you found the problem.

Ok the revving on its own has stopped however she confirmed yesterday with the AC on about 80 degrees going about 5-10 MPH the car stalled(quit) two different times. It restarted without too much trouble but for some reason it continues to stall occasionally usually only with the AC on.

Can anyone help me?

Maybe fuel pump relay going bad?

yep..probably relay,just a coincidence it happens when the AC is on.

I replaced the fuel pump relay from Eeuroparts approx 1 week prior to me starting this post thinking that the dying was what was causing it. Any other thoughts.

Thanks

How about the fuel pump?

Tech,
The fuel pump hasn't ever been replaced and it seemingly is fine. How should I check it? Fuel Pressure? Other?

Thanks, Tech

You would have to connect a fuel pressure guage and drive the car with it on there till it messes up and see what the guage does.

OK thanks Tech. Is the fuel pressure is between 38 - 42 PSI?