Replaced Speed/Reference Sender, now fast idle problem
 

I recently replace one of the speed/reference senders due to a brittle and cracked connector. The car was running fine prior to changing it. Once changed, the idle runs at 2k and once warmed up. It idle correctly when first started, but slowly climbs during the warm-up process. The car is an '86 944 turbo. Any thoughts on what the problem may be? Any thoughts/comments would be appreciated.

Mike

Mike,

I would set the idle using the air bleed screw on the throttle with the motor warmed up. Then when it cooled I would seee if it cranked up & idled cold.


drew1

I thought of doing that too, but it simply strikes me odd that I would need to do that since the idle was perfect prior to swapping the sensor. It doesn't make since that I would need to reset the idle...especially so drastically. A little variation might seem acceptable, but 1,200-1,500 rmp (in my mind) points to something else. I just don't know what.

It can't hurt to try adjusting the idle as you mentioned, but again, just doesn't seem like I should need to.

Mike

I have no ideas.

Waiting to see what you find out.


drew1

I think i may have a problem with these sensors as well. where exactly are they located?
-Aston

Drew - I adjusted the screw a little and the timing backed down responsively, so I backed it down some more and left it. It was idling around 1,400 - 1,500. I noticed it fast idling again so I checked on it yesterday afternoon and the damn screw was gone. It will take a week to get one through the dealership. Aggrevation!!!

Aston - There are two cables at the back center of the engine compartment just in front of the firewall. Each connects through a metal support bracket and both attach to the top of the flywheel bellhousing. I don't think they have anything to do with the idle; however they are called the speed and reference sensor, so they possibly do. My beef is I only changed one of the sensors do to a broken/brittle plastic connector...now the thing won't idle right.

Mike

If the new brass valve does not come with threadlocker already on it, put some on it. Mine loosened and came out once. Fortunately, it landed on the engine and I was able to retrieve it. The medium stuff works well for me on that part.

Check your under engine tray. Maybe it is there.

Before you adjust any screws or wires or anything, make sure you have no exhaust leaks. Exhaust leaks can cause the to idle race and not go back to normal.

Mike,

Could you have damaged a vacuum line when changing the sensors?


drew1

To make it all even more confusing... :)

I don't think it is one of the sensors. On my turbo the idle was some times rising like hell as well. It went from 1100 to sometimes 2000rpm. It was crazy. I then re-aligned my throttle body (not your problem, as it idle fine before), and that took away some of the problem, but it sometimes just popped to 1100-1200rpm at idle. I now discovered that the throttle position switch is the evil. When i cleaned it up a bit the idle came back to a nice steady 900rpm. I think the TPS sends a signal to the DME or KLR wich then controls all kinds of things like boost, but as well many idle related stuff. When this switch has a bad connection it will result in strange boost problems and/or idle related issues. The TPS did it in my case...