96 850 Wagon

we will be driving along and the motor will suddenly rev up by its self. the car just starts to go like you mashed on the pedal,then back to normal. about 1.5-2 seconds . can be quite scary in traffic.very random. I found a vacum line unplugged and fixed another thinking that was it,no luck. this was with the cruise in the off mode. I put it in the on postion without setting it and it hasn't done it since or very mildly, I can't tell for sure because the gas pedal is a lot more sensitive than my VW van. the cruise stopped working on a regular basis a couple of years ago. could it be a short in the switch and the cc is telling the motor to rev even though it was in the off postion? anyone have this problem? how can I disconnect the cc,other than the fuse? is there a relay I can pull? thanks

 

You can disconnect the hose to the cruise motor which is under the battery tray.

 

I pulled the three wire connector that was under the battery tray. it went to the unit that was attached to the underside of the battery tray. is that what you were referring to?

 

That will do the same thing to see if it was the cruise causing it. There is also a black Vacuum like going to that pump that you could have disconnected to test as well.

 

well,it's not the cruise control. I pulled the wiring harness to the cc and still have the same revving problem. it went away for a few days and came back today after work,as bad as ever. any ideas what can cause this?

 

I would check and clean the idle motor.

 

I don't know much about her car.where is the idle motor located and how do I go about cleaning it,do you have a pic of the motor with it circled? a search on the net suggested the coolant sensor,that's what everyone on the VW forums for my van says to start with when your Vanagon is not running right. sometimes when the idle shot up I noticed the temp gauge would be low (like when you first start it in the a.m.) and then go back up to the normal operating range.

temp sensor from IPD:

http://www.ipdusa.com/version.asp?st...D=72&V_ID=2733

 

Temp sensor could cause it as well.

The idle motor is just infront of the throttle cable setup. There is 2 hoses going to it. It is a round cylinder looking thing.

 

what should I use to clean it?

 

Carb or Brake cleaner.

 

Since you metioned that this problem and the temp. gauge are related, I would check the connections/wiring to the coolant temperature sensor first. Any loose contact will make the computer think that the engine temperature is low and will rev the engine up.
Replacing the sensor will be the next step before cleaning the idle control motor.

 

The temp gauge isn't always affected,just sometimes it drops when the engine revs. so where is the coolant temp sensor located?

96 850 Wagon Turbo

 

This attachement might help.

 

thanks harry. I did find some info on replacing the t-stat,and the temp sensor is located under the t-stat housing. is it possible to replace the temp sensor without replacing the t-stat? or is it to hard to get at?

 

I took the electrical plug off the idle motor and cleaned that with cleaner,didn't help. I didn't see how it comes off to clean it further without messing up the hoses that go to it. it has those "crimped" on type clamps instead of regular hose clamps. the temp sensor looks o.k. no loose wires or anything. they can just wear out or go bad can't they?

 

It is possible to develop internal problem/weak points in sensor itself but many times the wires start to give up internally while the insulator part of it will still look good. Try playing with the sensor wiring while someone staring at the temperature gauge inside and also leave the car idling so that you can notice any change. (Safety first - make sure you stay safe from the moving parts).

 

if it was the temp sensor why would it cause the engine to rev to 3000 anyway? anything else that could cause this?

 

Because it would think the car might be cold and give to much fuel causing the idle to go high.

 

I just ordered the temp sensor and t-stat from IPD. I will install next Saturday and see if that does the trick!

 

I hope it fixes it.