This is the follow up on my xjs V12. I have to thank everyone who has posted all the "how to's" I removed and cleaned the aav, installed the red tps kit to replace the non functioning one, replaced the vacuum can on the distributor, installed new fuel pump and regulator's, cleaned the spark plugs. They were completely black. The compression was 175 to 180 all around. Was surprised at that. And then the moment of truth, car started right up!! Oh yea! Set the timing and drove it for the first time, did very well until it completely warmed up, then it would surge on light throttle. Went back to checking the tps, and noticed if I just unplugged it, car runs and drives perfect, no surge. So I'm not sure what is causing the injectors to cycle on and off at part throttle. I've been driving it since last Wednesday, and it's just great, on lake shore drive here in Chicago is so bumpy, but in this car it's smooth as silk. I love this car. I could not have done this without this forum, so thanks to all of you, I have my dream car.

 

The "could be" list might get a little long.

Double check that both throttles have a base setting of .002", the bores are clean, and the linkages adjusted so that both sides open equally. I'm sure Grant has posted a good write-up on this; I'll try to find it.

Cheers
DD

 

Is the close voltage reading on the TPS in spec?
Does it surge at tickover?

 

I Forgot to mention that I removed and cleaned the throttle body's and installed all new vacuum lines and air filters. Also set throttle to proper specs. Most of the things I've read on surging is at idle, mine idles fine. Surge happens at part throttle only, moving towards mid to wide open it doesn't. Also tps is .033 at idle and 4.20 at full throttle, with no drop out. Also tried another one from Engle, and it still surges. But it drives perfectly unplugged? Not sure why, but I don't care. Thanks for the reply.

 

The TPS low end voltage tells the ECU the throttle is closed.
If you step suddenly on the gas the TPS voltage at the ECU rises rapidly and tells the ECU to add extra fuel.
At part throttle the TPS should give a fairly steady voltage and that should do nothing at the ECU.
So what is wrong ?
1. You replaced TPS, no change.
Also disconnecting TPS fixes problem.
2. TPS wiring or connector intermittent.
3. Fault in ECU ( very rare but possible ).

 

I forgot one thing about the TPS.
If it tells the ECU the throttle is closed above the fuel cut off engine RPM ( 1500 RPM ? ), then there is no fuel injection.
That saves fuel when cruising along and you close the throttle because you are on the over run.

 

The car should not run properly with the TPS unplugged, so something is very wrong.
I have had a few thoughts as surging is a symptom of the ECU thinking that the throttle is closed and the revs are swinging above and below about the 1400 rpm level, so it switches on and off the overrun fuel cutoff:
Check that the vac line from the balance pipe to the ECU is holding vac.
Also do continuity tests on ALL the loom wire from the TPS to the ECU.
Also check that the throttle spindle is actually turning the TPS when all installed.
Also check that the full throttle enrichment circuits (capstan switch and vac switch) are working as they should and no continuity problems.

 

If it's the same as my 1990,,, proper specs at the throttle/capstan is a voltage and the position of the throttle at idle aught to be (memory) between .32 and .36 v... There is a green, red and yellow wire set off of that TPS and the measurements come off of the (memory) yellow and red wires. Please, if someone could correct my errors here if need be...?

 

That is a good point. It is stated the car performs well with TPS not connected.
If the input circuit for the TPS in the ECU is not biased to ground ( which normally you do with this type of input ) then the input can float and tell the ECU the throttle is NOT closed.
Then you do not get the over run cutoff effect and presumably no surging.