About 5 weeks ago, I acquired a beautiful 2005 Jaguar S Type VDP. It's had two owners, only one of which ever drove it; apparently driven lovingly by a little old lady. She drove it for 8 years, and then intended to give it to the teenage son of a friend. However, because of medical conditions, he was never able to drive it. It sat in their garage for a couple of years, before being ultimately moved into a farmer's field, where it sat for several years. Based on the oil change sticker, it hasn't been driven since the summer of 2013. When I got it, there were at least hundreds and probably thousands of pecans and walnuts chewed up and stuffed around in the engine compartment. 17 separate plugs were chewed off from their wire connectors.

I got it all cleaned up, pulled out the old wiring, and put in a new wiring harness, changed the rear brakes, replaced the Throttle Position Sensor, the Fuel Pressure Sensor, and the vacuum line from the Fuel Pressure Sensor to the Throttle Body.

I also replaced the Intake Manifold Gasket and took the Throttle body off and gave it a good and thorough cleaning. When I did, I noticed that the butterfly valve didn't close fully - not even close. This is apparently adjusted via a screw (the idle adjuster?) on the side of the throttle body, so I adjusted it such that the butterfly valve closes (or at least almost).

After some initial adjustments, the car now sounds fantastic (accompanied by the pleasant smell of roasted pecans). It idles at about 800 or so RPMs. On to the road test.

When I put it in drive, the car immediately pushes forward, like those horses want to run! Constant, considerable brake pressure is necessary to keep the car from running away on me. Without braking (and without gas), on the open road, the car will accelerate to about 40 mph. And to stop the car, brake pressure must be very firm.

What's going on?

I read on some of the threads that after changing the TPS and/or adjusting the idle, the car needs to re-learn things. Is a hard reset all I need to do to get her running properly?

As always, your considerable insight and wisdom is appreciated!

 

Hmm, I don't know what to tell you about that adjuster screw on the throttle body, but that doesn't sound right. Unless somebody has previously messed with it, I don't think any adjustment was required. Did you keep track of how much you turned the screw? Did you ever try running the engine before adjusting it? Have you tried turning it back? Doing 40MPH with your foot off the gas isn't right.

 

+1 it's due to the TPS mod. Sounds like it's beyond the ability of the PCM to correct for it.

 

So, the screw functions as a physical restraint that prevents the butterfly valve from closing. As a result, the valve's minimum resting position left the throttle body open about 1/4 inch. My understanding is that that's not supposed to be the case.

 

That may be wrong. Where on earth did you get that understanding?

For sure, you are NOT meant to alter the setting from the factory.

I suppose you could hope it's not too serious and also hope there's some other problem - maybe an air leak? - and go hunting for whatever else may be wrong.

 

Check the stickies for this forum. There is one for throttle body calibration

 

600rpm is idle


what throttle position % does obd say you have