I have been struggling to find what I think must be a vacuum leak. I've had the car ('90 Sovereign w/ 39k miles) for 8 months and since acquiring it, it has always had a high idle. Hadn't paid attention to it, figuring it was something I'd address in good time after chasing down other small issues. Then, a couple of months ago, I started to gradually notice a variable high pitched whistle after the car was warmed up and idling. I've poked my head under the hood time and time again and can't tell where the hell the noise is coming from. If it's a bearing starting to fail, I've never heard one sound like that in my 45 yrs of tinkering with cars. Using a stethoscope has failed to find the source. All I can think of is a vacuum leak that's creating the whistle.

Last week I was once again searching for the errant noise and discovered that the EGR pipe going from one side of the engine to the other was loose. Eureka! Hoped I'd found a likely cause of the whistle. In trying to access the fitting end beneath the manifold, it seemed the only logical way was to first remove the throttle body. And besides, I figured it was a good time to clean the throttle body and MAF and check the clearance on the throttle body butterfly. It wasn't until I had removed and cleaned the throttle body that the light bulb went off; why wasn't there a gasket between it and the manifold. And while we're at it, where is the gasket that goes between the throttle body and the air horn? How does a gasket on a low mileage car with few signs of having been worked on just disappear?

At this point, I was hopeful that resolving two issues (gaskets and tightening the EGR pipe) as well as confirmation the throttle butterfly was correct, would eliminate the whistle (vacuum leak?) and the idle would magically drop to where it should be. But of course, no such luck. It was at this time that I noticed that the whistle wasn't as pronounced though still present once the car was warmed up. And then I realized that if the engine was at operating temperature but not running and I started the car, it idled at 750 rpm and did not whistle. As soon as I drove off, the whistle and high idle appeared when stopping for a traffic light or putting the car in neutral.

At this point I don't want to play with the idle speed adjustment as I think it is a symptom, not the cause, even though it has always been present and the whistle appeared later. Any thoughts out there? Do others agree that the symptoms are indicative of a vacuum leak? Or should I be looking for something else? What vacuum operated system in the car isn't activated until accelerating and then creates an open passage through a vacuum line that could be leaking and then deactivates after the engine is shut off? Or am I fixated on the possibility of a vacuum leak and should be looking elsewhere?

 

Quite the conundrum!

I will add that the manifold to throttle body union isn't usually gasketed but you can of course cut one and fit it if you think the joint is leaking un-metered air. I added one last time I had the TB off.

You can also check the tightness of the various vacuum hoses at their connection points as they get hardened over time and the push-fit can get rather sloppy.
Cutting an inch or so off each end will usually give a fresh, tighter connection.

The large rubber bellows at the TB is easily mis-aligned and trapped with a fold at the connection so it too can also be a source of a vacuum leak. Some vacuum hoses connect low down to the purge valve, worth a look down there too.

Good luck with your search!

Larry

 

No gaskets upon assembly? Yet they're shown on the parts diagram. Okay, I'm surprised but that would explain why there is no evidence they were ever installed. In any case, there are gaskets on either side of the throttle body now.

Hmmm.... Purge valve, you say? And then there is the other issue I've recently been dealing with. Fuel Fail 89 = purge valve. So I replaced the valve and one vacuum hose and cleaned the electrical connections but still getting the error message. I had planned to go back to that corner of the car and take a closer look at everything in there to see if anything else was amiss. Makes me think I might have a problem causing the Fuel Fail 89 that is related to the other issues.

 

The parts diagram is often haywire as it sometimes covers all model year variations. The TB gaskets were probably a delete, possibly used at first but then deemed unnecessary. My 94 didn't have one and also there were no gaskets on the water rail, also a delete but re-introduced on subsequent models. For a real treat, compare the rear suspension diagrams with actual assemblies used on late model cars!
FF89 does seem rather specific to the purge valve, did you follow the flowchart in the engine management.pdf to correct the code?

Larry

 

Hi Tony,

I think all of the 4.0L cars had no throttle body gaskets, just finely-machined mating surfaces that don't usually leak. I'd be more inclined to think your IACV is clogged up with carbon and not closing properly, or you have a leak in a crankcase breather hose, vacuum hose, or air intake plumbing.

A problem with the purge valve could mimic an air leak if it sticks open or doesn't modulate properly. I dealt with FF89 on our '93 and off the top of my head, I think the key was to clean the ground point on the left inner wheel well, but I may be wrong. It is also a good idea to clean the carbon out of the purge port, which is part of the same assembly that the EGR pipe connects to on the underside of the intake manifold. You have to disconnect the EGR pipe and remove the port assembly to clean it. Mine was completely clogged with carbon. I used drill bits and wire brushes to carve the carbon.

I'm not sure if the secondary air injection system can cause high idle, but it only operates briefly at startup.

Cheers,

Don

 

Thanks all for your replies.

I will revisit the procedure for clearing the FF89 code but as the battery was disconnected for several hours, I figured that would be sufficient.

With respect to the IACV, it was quite clean when I removed it and checked. A light dusting of soot which I sprayed with MAF cleaner. I have a procedure for setting idle speed from Jag Lovers which I have yet to implement. Is there a procedure for first confirming that it's working correctly? Can a voltage be applied to it while on the work bench? The EGR port appeared fairly clean when viewed with the TB removed; just a bit of carbon build up around the perimeter of the port inside the intake manifold. Given the nuisance of removing it (I'm not thrilled to remove the TB a 3rd time), is it likely that the intake end of the port won't be much dirtier than the outlet end inside the intake manifold?

Again, thanks to all who have replied to this and my other inquiries in past posts.

 

The IACV stepper motor has two coils that require two offset pulsed signals to operate, so I don't known of a safe way to test the motor on the bench. If you connect the motor to the vehicle's harness and attempt to run the motor without installing it in the valve body, you run the risk of the pintle threading all the way out of the motor.

 

If you haven't already done so, it might be an idea to remove the IACV housing (you will need to cut or buy a new gasket to reinstall it) and clean the carbon out. Lots of us have replaced the IACV chasing issues but I think a lot of times, replacement was unnecessary and rarely cured the issue.

You say you haven't followed the procedure for setting up the idle yet? I would think that would be job #1, no?

The battery disconnect will clear your code so no issue there.

keep at it,

Larry

 

Again, thank you all. Am waiting to perform the idle speed adjustment until after I've exhausted all possibilities of there being a vacuum leak as I believe a small leak will affect the idle. But if the "whistle" noted in my original posting isn't a vacuum leak and I can't isolate it to a component possibly suffering a bearing failure (and no, I've never heard a failed bearing sound like this), what the hell could it be??? It's frustrating because I can't seem to locate the source of the whistle. I'm beginning to wonder if it could be the transmission or ???.

 

mmm ..the old "what can it be" syndrome peculiar to 30 year old cars .....to prevent insanity, best cure? turn stereo up

Larry

 

One trick that might help locate the whistle is to use a 2,-foot section of rubber tubing as a stethoscope. I find this better than a mechanic's stethoscope for locating air leaks and whistles.

A smoke test might be the most definitive method for locating leaks. If you already own an air compressor, you can build a rudimentary smoke machine for around USD $20. See YouTube for various construction methods.