Hello all;

I have high idle RPM (1250-1500) on my XK8 2002 that will not go down! I checked air leaks, changed the throttle body, and re-sealed the TB Gasket, no use.

I get errors related to O2 sensors (all 4 appear to be out) (P0031 P0037, P0051, P0057, P1646). also I get P0010 and P0020 related to VVT circuit malfunction (solenoid related malfunciton). I also get P0507 "Idle higher than expected"

Could any of these be responsible for High RPM? or should I keep chasing air-leak ghosts?

MJ

 

Eliminate the simplest possibility first.

Is the Throttle Cable properly adjusted or is it too tight and preventing the TB plate from closing?

Graham

 

Good call, but not related this time. Cable loose and disconnecting makes no difference. Also, when revved, rpm takes it's sweet time coming down again..

MJ

 

New TB so the return spring has to be OK and it can't possible need cleaning!

Did you disconnect the battery before removing the old TB and reconnect after the new one was fitted to reset the fuel trims to default?

Graham

 

Another good guess..

After fitting the re-manufactured TB (ASI), I took the battery off, shorted the car + and Earth cables for 10 min, then fitted the battery back. After that, according to ASI instructions, I held the switch to the on position for 60 sec before firing up.

I must have done all of this at least 5 times, no difference...

I take it you don't believe O2 sensors could be a cause, no?

 

p.s. I do appreciate your comments, thanks for the help

 

It wan't easy.. but I finally got the RPM down, and with a little bit of help from ASI who supplied the rebuilt TB, and a lot of help from Shots in the Dark Inc.

The ckeck list pre-resolution (didn't work but may be useful reading):
1- Reset sensors (disconnect + and – battery cables, short them for 5 min using jump leads, reconnect, place switch to the on position before ignition for at least 1 min, hit ignition)
2- Clean mass air sensor with non-residue electrical spray (I saw a good technical note on this at the "how to" thread)
3- Checked for cracks in air pipe, the ribbed part becomes brittle with time. I did have a small hole and I'll submit a separate thread on a useful product I found that helped with this.
4- The air pipe has a habit of slipping off at the mass air sensor pipe leaving a decent gap for an air leak
5- The air pipe is nice and snug onto the throttle body, I wedged cardboard between the gasket and air tube to push it into a tighter seal with the TB
6- MAS base air leaks could also happen
7- JITS says to also check part and full breather hose connections for leaks
8- It is possible though unlikely that the TB base gasket is leaking (the one between the TB and the elbow), I added a thin layer of gasket silicon to both sides of the TB gasket to ensure tight closure. the down side is that last I checked I could not remove the TB from the elbow! I topped trying and could not recommended this
9- Reset TB sensors again after all possible leaks eliminated
10- I saw another good technical note on the "how to" thread to ensure that all the wires connections are making good contacts.
No use


OK, now for what actually worked:


ASI says that when all else fails, adjust the position of the TB sensor by undoing the two bolts holding it in place just enough to nudge sensor; the holes in the sensor assembly that the bolts go through have a lot of space for adjustment.
I looked into the bolts and they looked like torx 20. But a closer look revealed something altogether more sinister, a pentagonal star!
I spent the next week looking for a bit that would fit into them darn bolts (I think called pentalobe or something just as silly), and finally found a full set for ~25 USD. I think I used the size 20.
Armed with tools, and while lovingly and repeatedly burning my knuckles on the TB and engine, I managed to undo the bolts a little. Nothing happened. I nudged a bit, nothing happened. I nudged a bit more, the sensor jumped about 2 mm all the way back (towards the rear of the car) and the engine stalled. Brown pants moment
I moved the sensor back to where I thought it was before (or maybe .5 mm towards the rear of the car) and tightened the screws again. The car started fine but the RPM stayed the same at ~1200-1500.
As I was contemplating giving up, I reset the sensors one last time by removing the battery like I mentioned before.
Started the engine
RPM 600-650 for the first time in a month.
Basically, yay
Been driving for a couple of weeks now, no problem.
And that, ladies and gentlemen, is the sweetest shot in the dark… Thank you SitD Inc.

 

Great post. Very thorough. Thank you