1996 XJS with 4.0

i obviously have a vacuum leak. My short short term fuel trims are in the double digits at idle...they go down to single digits, even zero when accelerating.

the idle is lumpy.

i hear a hissing sound coming from under the throttle body. Is there anything down there that can be causing that sound? I tried using a rubber hose to direct my hearing, and there's definitely a strange noise coming from under there. I can't see what it is without pulling it out.

are there any spindle gaskets, or some gasket internal to the throttle body that I might not have seen before?

i recently took the throttle body off and gave it a good clean down. The TPS, O2 sensors and MAF sensors all seem to be doing a good job.

 

There may well be one or two small diameter spigots under the TB. If you can get a finger under it and see if you can shut one off with your finger. Once you have found it, a silicone blanking cap, or a short length of fuel hose with a small bolt in the end, will do the job. If necessary, remove the TB and look.
Greg

 

There are vac pipes, plastic on mine, under there, and easily damaged when changing the oil filter.

Here are 2 parts drawings showing some detail.

 

Thanks, those are two different throttle bodies. I have the one up top. There is a hose for coolant under my throttle body, but no other connection. I'm thinking that's probably the hissing noise I'm hearing.

Unless theres something that can go wrong with the way the butterfly splindle is kept in place, I may have to (a) do the cigar test, (b) do the propane test or (c) take it in and have someone with a professional smoke machine find it....but where's the fun in that?

 

Also check the intake bellows at the throttlle body. They tend to split on the underside.

 

From a generic view point:


1. Throttle body to intake joint might leak. any opening 'behind" the butter flies is seen by an engine as a leak!!


2. The spindle shaft in the throttle body can "leak".


Carl

 

1. Propane test was utterly unsuccessful. Could not get engine to respond no matter where I put it.

2. Smoke test was way more successful:

a. IACV has smoke coming out of it. Literally coming out of it. I had to unplug the harness connection to see if it was really coming out of the unit, and it was. Around the metal tube. I believe it was coming from out of the gasket as well.

Question 1: Should the IACV be leaking air? I'm thinking no. I own a new gasket, and even checked on line for a new part. The new parts show a rubber o-ring. I'm not sure I've ever noticed an o-ring on these parts before. (I happen to have two salvage IACVs, neither has an o-ring)

Question 2: eBay has two IACV's for sale. One for $150+ and another for $20. Anyone have any experience with the $20 part?

b. The throttle body looked like it was leaking too, from underneath, but since it came from the direction of the IACV, I couldn't be sure. At this point, I'm going to assess the IACV (with your help).

 

I'm an idiot. The gasket I added to the throttle body didn't account for the "notch" in the throttle body. Basically had a gaping hole sucking air in.

Removed the gasket, and dressed it up with some Hylomar AF I had. Problem solved, engine is smooth again.

 

yeah, I got the ROADFAR brand for like 15 and it came clean, well constructed, and perfectly working. F paying 150...its a small part. Mines been working beautifully. That second bolt, one closest to cabin area, is A PAIN to get to, I was unable to remove it with the tools I have.