Random(?) high idle

[UhOh]

Driving the wife's car the other night and at a stop light I looked at the tach to see it at about 1,050 rpm. Car was warmed up, well above the 140 degree range. Dash gauge showed the normal 190. Ultragauge showed nearly the same. Shortly afterwards the idle speed showed up normal (903 rpm). No codes popping up on the Ultragauge.

Never seen this before. I suspect that it's the CTS: doubt that it can still be the original black one (2000 car, now with 204k miles). I'll be ordering a replacement to put in, but... Anyone have any other guesses?

I need to knock the timing back down a bit (it's peaking at and just above top-line) and adjust the IQ (I can sense a little slow-down shudder- I think it's time to hammer mod this thing).

 

[wonneber]

The CTS on mine is 2 part. 1 sensor for the gauge, 1 for the ECM.
Does your CTS have 2 or 4 wires?
Don't know if U-gauge can show both.
There's a fuel temp sensor inside the injector pump.
Not sure if that would cause it.
The quantity injector might be having a problem also?

 

[UhOh]

Yes, it's the standard 2-circuit CTS. That's why I said that the Ultragauge (which is reading from the ECU) showed a normal operating temp: though, I don't know whether there could have been a transient signal from the CTS that resulted in the ECU adjusting to the higher idle (and the Ultragauge smoothed out that transient dip).

The car runs very well. This kind of was one of those WTH moments.

For now I'm just kind of marking this as a point of interest. I'll note if there are additional instances: will also report back on what I find on timing and IQ.

 

[oilhammer]

Different car than yours, but I had a BRM Jetta in here not long ago that would randomly fast idle for the owner. No DTCs stored, and it did not act up for me. However, I noticed the engine barely cranked when I went to start it. The BRMs start so easily that it is often tough to even notice a slow crank, but I for sure noticed it.

Checked the battery, and it was not even close to passing the tests. Replaced it, and of course as I always do I made sure the main connections were clean and secure, but told them I never did find anything with the mysterious random fast idle, despite him saying it happened at least once a day.

He called back a few days later, and said not only has the car started quicker, but the idle nonsense had disappeared.

So, as always, low voltage can and often does cause all sorts of odd behavior. ECUs do not like it, and do not cope well with it. If nothing else obvious stands out, I would check and clean any and all main power and ground points on the battery cables, as well as make sure the battery itself is in good order.

 

[UhOh]

Brian, that makes perfect sense! I'll take a closer look at the battery: I've had this brand new load tester that I haven't yet used (my time has really been short of late). With all the cars I have to keep track of I'd kind of confused this one with the daughter's: I'd recently looked at everything, electrical's charging output etc. and found to be good.

Batteries are a minimum of three years old now: I have no records of when the POs had repalced.

 

[oilhammer]

Well it never hurts to check those things. Remembered another time when I had a customer's car, 2000 Jetta 2.0L, with an ABS light on, had a hard DTC for the fluid pump. Repair was a new ABS assembly. It was random, but usually had the ABS light on. One time when I had to replace a worn out clutch on the car and obviously had the battery disconnected and ground cable off, I cleaned it all up just because it looked kinda crappy. Guess what? ABS worked fine and has worked fine ever since... and that was easily 10 years ago!