Wow, I've never seen that before. Seems like a good idea. I always thought it was odd that the manifold and throttle body didn't have a gasket between them, even a metal one!

I'd get it...

 

I ordered a gasket and it came in today. Will put it on tomorrow. I don't like the idea of no gasket. It's an OEM Jaguar part in the original packaging.

Still have not solved the fast idle problem though.

 

OK Guys, Everything else has checked out fine but the problem still persists so let me know what you think about this possibility...

I am beginning to wonder if the Air-Pump system could be causing this somehow? That thing has acted up before on this car ~ Every now and then the car will blow smoke out the tailpipes (car uses no oil) and then just suddenly stop again after 30 seconds or so. This only happens once in a great while. Usually shortly after I just get on the interstate and start to open it up after only driving in the city and sitting for a while. We're talking maybe once every 4-6k that it does it and then it goes away again for another 4-6k. An experienced Jaguar person once told me it was the air pump system and as long as the car ran all the rest of the time the occasional 30 seconds of burping some smoke was ok, that it was just the system opening the gate and some built up carbon was burning off.

I am wondering now if that system could have gone further down hill and be somehow causing this idle thing?


I know some people even remove the system, Kirby's book even tells how to get rid of it though the instructions seem to apply to earlier cars because they mention a pulley and the pump on my '96 seems to be electronic, which you would think would make it even easier to remove. Any thoughts? I live in a state without inspections so that part is not an issue. I know part of the reasoning for removing the system on older models was the clutter under the hood but mainly the belt-driven pump ate up engine power, I'm not sure if that is true with the new pumps which are electronic with their own drive motors internally but that doesn't mean they can't still be sapping power from the engine somehow? and of course there is still all the extra under-hood clutter getting rid of it would remove. Another question that comes to mind on '96 models with the OBDII system is would removing the pump cause codes?

 

SouthernGypsy, I replaced many parts and had no luck with my slow idle until I replaced the TPS. All was well instantly for about a year. Suddenly the engine started the fast idle as yours is doing. I replaced the EGR valve and all was well and has been for over 2 years. It idles at a perfect 600 rpm after warm and only 750 when starting cold. No PDU or any other diagnostic computer was needed. The part was about $57.00 on EBAY and fits General Motors OLds and Buick. MFG part #REPP509201.


I also bought a new TPS but have not installed it.
Luck, RagJag

 

well the OBDII scanner says the TPS is working properly as well as the ACV and EGR. In tests all of those show to be working properly and the throttle body is clean as a pin everywhere as are all of those, and no sign of a vacuum leak anywhere.

 

I wouldn't rely on the OBDII/ECU as an indicator that something is working 100%. OBD2 is awesome at telling you when something is wrong, it is terrible at telling you when something is working well.

I've had idle issues with no codes for a long time. Now I did once have a failing EGR and it did throw a code eventually, but it had to stall on the highway for me to get that code.

The TPS is a device that will rarely throw a code when failing because it doesn't fail all at one time. It develops "low points" that usually cause driveability problems for the car. If you have checked the voltage reading on the pins of the TPS at idle (should be 0.5v), then you are probably fine there. The TPS on this car has been known to wreak havoc without throwing any codes out. Still, I don't suspect the TPS is at fault.

I really believe you're only solution is to find a shop that has a WDS and can reset the idle for you. I've had this issue on two cars, and both times a high idle was instantaneously solved with a trip to a shop with the right computer. Its a simple $150 fix.

The only other suggestion I have for you is to see if a manual reset of the IACV will work.

1. Run engine until you reach normal operating temperature.
2. Switch ignition off.
3. Switch ignition on, wait 5 seconds, then disconnect the connector to the idle speed controller.
4. Switch ignition off.
5. Wait 15 seconds then reconnect idle speed controller.

6. Repeat two more times.
7. On last repeat, do not reconnect idle speed controller.

8. Start the engine.

Check the base idle speed, which should be at 550-600rpm. If the idle speed is not within these limits, then adjust the air bypass screw to bring the idle speed within these limits.

Switch ignition off and reconnect the idle speed controller. Start engine and check to ensure that the idle speed is between 650-800rpm.

 

When I say I'm using OBDII, I'm not referring to just checking to see if there are codes or not, in case that's what you thought I was referring to.
My reader actually lets me SEE the live readings (resistance, voltage, temp, pressure, etc. depending on the sensor) from the sensors as the car starts and warms up and/or I do different things like tun on AC, etc. or slowly open/close the throttle body by hand with the car off but ignition on. Now that doesn't mean they are in the correct range since I don't know (and haven't found) what the correct readings should be for each one, but I do know they are at least working as in responding and varying the data in response to different stimuli, so I know they're not just sitting there "dead" in other words.

But I did try your procedure and it made no difference, the car is still idling at 1300-1400 RPM (fully warmed up, in fact just got back from town in it) and turning the screw will not lower it; You can't turn it clock-wise at all (seems to already be in as far as it will go) and turning it counter clockwise makes it go up even faster, if that is an indication of anything.

 

SouthernGypsy. What is keeping you from replacing the EGR as I did. Little cost. I did and it fixed my fast idle. The Jaguar PDU is sometimes called PRETTY DAMNED USELESS by technicians that use it.
RagJag

 

Actually I picked up one this morning, took until today to come in, but have not had a chance to put it on yet, though I hardly call $187 "little cost", it's probably the single most expensive EGR valves I have ever bought in my life for anything. You must be richer than I am. I got it because it was the ONLY thing my local parts store actually had in stock at their warehouse, though now they will have me a temperature sensor (for computer, not the dash gauge) tomorrow morning. If I put it on and it doesn't work they will let me return it. I'm waiting on the car to cool down enough to change it now.

I ordered the temp gauge because I had my picked up my dad while I was driving around with my OBDII scanner plugged in, checking readings as I drove, and he was looking at it (he's a retired 45+ year master mechanic and has never seen a hand-held OBDII reader that does everything mine does) and he happened to ask if 171 was normal running temp for my car, something I hadn't noticed before but while the dash gauge shows the needle just on the low side of the N mark in the middle, the OBDII shows that the computer thinks the car is never getting above 186 degree... That's the highest we seen in both traffic and on the highway on a 73 degree day, it's more often in the 170's range. So that made me wonder if the temp sensor could be bad and causing the computer to think the car is still cold and keeping it at fast (cold) idle. If it could be that stupidly simple. Hey, sometimes the simplest things are the easiest to overlook.

 

Got it installed but a New EGR valve did not change anything.

 

You couldn't affect the idle using the method above? To me, that indicated a problem with the IACV. When I had idle issues, I was at least able to slow it down temporarily using the method I mentioned above. That cleared the IACV as a potential part failure candidate.

Make sure you follow the procedure, but if you can't get a good idle, I'd have to lean towards that.

The coolant temp sensor and sender are two different parts. The gauge could be off while still reading the temps correctly. If your scanner is showing the correct temp through the OBD port, I would not concern myself with what the gauges say. That's a different problem for a different day.

 

Oh, as far as the temp goes, if your thermostat is stuck open, which is common for old thermostats (happened to me) it could explain the fact that your car is not getting to the correct operating temp.

Change the thermostat. You will need to order a gasket as well. It will not cure your idle problem, but it will help your mpg.

 

Yes, I could affect the idle, I could make it faster... but that's worse. Seemed like I needed to turn it the other way to slow it but it was all the way in already, which it seemed odd to me that it was turned all the way in and has apparently been that way for a long while, if not the cars whole life, or is that normal?


Yes, the gauge says it's in normal operating range, the OBDII says its running what seems kinda cool. What is the normal range for these?

 

190F should read "N". (Within a degree or three)

I'm thinking you have a bad IACV or you need to get the idle reset by a shop.

I believe if you pull the temp sensor plug and short it, connecting the two contacts on the plug, it should default to a properly warmed up car. I don't see that resolving your problem though. It shouldn't drive your idle up like that.

So let me recap:

1. Vacuum leak
2. TPS needs to be 0.5v at idle
3. Idle Air Control Valve bad
4. Reset base idle using computer

Unfortunately, I think the order of probability is in reverse order. (#4 being most likely to resolve, then #3...)

 

Southern Gypsy, I am sorry the valve didn't fix your idle. To further explain what I did let me say that Auto Parts Warehouse has the same valve I have and it's part number is REPP509201. They sell it for $87.00 It also fits Oldsmobile cars. What part number is your valve? If it is the same as mine I can only think that your engine is getting quite a bit of extra air into it that is coming from some other source.


I am not rich at all, being a retired semi driver from UPS. I consider the price you paid to be quite a bit too high. Is your valve made by GM as in Delco Remy? They are priced higher but I haven't saw one near $187.00.
I will shut up now.
RagJag

 

Well I had to go to the parts store anyway for something for one of our work trucks so just picked up a new thermostat and the temp sending unit for the computer since they had both in stock and wasn't badly priced. Letting it cool again now with the hood up. Will swap them out and fix that as soon as I finish with this truck, should be cool enough by then. Though I'm like you, I'm dubious that the computer thinking it's not warm enough would cause this much fast idle (though it is actually about right for a cold idle speed).

 

At O'Reilly auto parts they gave me BDW part number EGR1095 and even with our ranches discount (which is a good one) it was $171.59 (sorry, I had something else on the ticket making it $187), the list was $281.34 normally but we have a commercial account for our ranch and get a pretty large discount on most parts. I can take it back if you have a cheaper GM part number that you know works well on these cars. This was the one they showed specifically for a '96 XJS 4.0L with an Automatic though.

 

Hum, my old thermostat was a Waxstat made in England, and rated at 188 degrees, not 192 degrees like the parts store gave me.

 

That's the original, so it's likely failed open.

I suspect 192F close enough

 

You'll need a gasket