Apologies if this seems like a newbie question. My car is an 01 XJR.
So the other day, I start my engine and upon start up, my RPM goes up to like 3500 RPM....then a few seconds later, comes back down to a normal 1100 or so. Also there are times when I am driving and although my foot is not on the accelerator, the engine revs up a little bit. It seems to rev on it's own. For the most part, it drives fine otherwise.
Any suggestions on what it could be? Could it be the secondary chain tensioners?
If the ECM looses its fuel trim information, primarily due to loss of battery power it will rev high, usually only to about 3k, for a couple seconds then drift down to normal RPM. Your second statement does, indeed sound like the throttle body, or rather the Throttle Position Sensor.
A quick clean of the throttle position sensor connector might help you, a 5 minute job. Had the same symptoms a year+ ago, cleaning both halves of the connectors' pins with Radio Shack contact cleaner/lubricant took care of the issue - corrosion on the pins due to dissimilar metals (there's a TSB about this).
I hate to admit this, but my car did this just last week, and after several starts with high revs, I got a CEL light yesterday. Taking the laptop home today (the one with the autoenginuity program on it) to discover what is amiss. I'll repost up when I have something to diagnose.
Thanks everyone for your suggestions. I will check out the the throttle body sensor and keep you posted. Sean B, I do not get the engine warning light. I do have the ASC/ABS not available light, but I don't think they are related.
My CEL cleared itself after a few days of the rough starting condition. My code reader observed the multiple misfires on bank 1 only. It also captured the data from the CEL appearing, and it showed my air intake was only 0.99 lb/min...which at normal idle, is around 4 lb/min. So, I removed my air pip and mass air flow sensor, cleaned the inside with the special MAFS product, and then did the connector harness and receiving pins with electronics cleaner...as they were dusty (and never been cleaned). Snugly reinstalled, and the line coming off the elbow of the pipe nearest the TB is very loose, perhaps that o-ring is getting tired. I removed, cleaned it, and snapped it back on. Starts have been much better following this cleaning a few days ago.
To be completely honest, I am very inexperienced when it comes to working on cars...so even something as simple as cleaning the connectors on the sensors takes a lot of time for me...since i need to research first exactly what it is you guys are talking about...then trying to locate it in my car. I know...pretty pathetic. I haven't had time to look into this yet. Hopefully I can get around to it this weekend.
The high rev at start up is the only issue for now...other than that...the car is running fine. I will keep you posted.
Mike, call me when you have an hour to work on this, i'll be happy describe to you what product to get, and walk you through the process over the phone. I'll PM you my cell number to keep handy. Tools needed - 10mm socket and a small ratchet or one of those screwdriver/socket drive tools, plus a phillips screwdriver.