I recently purchased an 85 XJS that has had too many hands on it. The car will start sometimes and the engine will idle at 2000 rpm. Other times the car will start and barely maintain 300 rpm (im kinda guessing on the low RPM as the tach doesn't read when it does this)

I have replaced the plugs, wires, cap, rotor, The AAV and all the vacuum hoses on the right bank. The vacuum hoses were off several ports and routed incorrectly. The distributor cap was broken in 5 pieces.

I have 36 PSI fuel pressure.

I know the car sat for a couple of years before i bought it.

I'm not sure where to check next. I hope someone out there has experienced this problem.

Thanks in advance.

 

Have you checked the throttle butterfly stop positions? You can check them as is, but you’ll want to remove the rods from the capstan before setting the gap. If the butterfly valves are being held open the idle will be high.

 

Yes, I have made sure the butterflys are closed.

I have sprayed carb cleaner around looking for more intake leaks as well.

But like i said, sometimes it will idle, high other times it want idle at all or just barely.

 

Throttle position sensor? Check the voltage its outputting, there's a sticky for it.

 

Sorry, I'm new to the forum. Where do I find the sticky?

No I haven't checked the throttle position sensor.

 

Well, looks like its not actually stickied. Post 2 of this thread, its a word doc. https://www.jaguarforums.com/forum/x...or-tps-229086/

 

Thank you for your reply,

I will look into it tomorrow afternoon,
We might be onto something. after reading the other thread it occurs to me that when at very low idle it does surge. Now when the idle is at 2000 RPM it is smooth. No surging.

 

OK, I finally got a chance to look at the TPS. I want to verify i'm checking this correctly.

Should I be measuring across the red and yellow wires? As in one lead on the yellow and one on red?

If so my voltage is WAY to high I'm measuring 3.53 across the yellow and red wires.

 

The attached will help.

 

Yes, red and yellow. The TPS is adjustable so, if it isn't otherwise faulty, you can bring the closed throttle voltage down to the required .32-.36 volts, which I'm sure you'll do

But....

If the engine sometimes idles at 2000 RPM then you sometimes have too much air coming in....from somewhere.

Next time this happens block-off the AAV inlet (on the back side of the LH air filter housing) with your thumb and see if the engine speed drops

Meanwhile, when the idle is very low....300-400 rpm as you mention....use the adjustment on the side of the AAV to bring the engine speed up to 600-700 rpm. I like to do this with the throttle rods removed

Cheers
DD

 

Just to clarify, do you literally mean closed?

The throttle blades are supposed to be set to a .002" gap

Cheers
DD

 

Doug,

I forgot to mention I found the high idle problem, and its a little bit embarrassing I had the right side air cleaner off to replace all the vacuum lines. I hadn't reinstalled the air cleaner not realizing the 4 bolts that hold it air cleaner base to the intake were not blind holes.

Now it will only idle very low with some surging if you can get it to idle at all.

I will adjust the TPS and see if i can get the voltage down and I will also make sure the voltage increase is smooth.

Yes by closed i mean they are set at .002"

Thanks for the conformation.

I will post again after I get the TPS checked out.