I'm in a bit of a jam here, was wondering if I missed anything obvious. 1985 XJ6 4.2L

Last night I changed all of the vacum hoses to the power booster on the brake. Suspecting a leak in the power booster I put some soapy water on the booster seams, took a hose and blew into it. Sure enough the bubbles showed a leak. I used a sealant to seal the leak. Everything was working fine at this point. I tell you this just go give you the whole picture.

I had to remove the air intake between the MAS sensor and the intake manifold to reach the vacuum port. While it was off, I noticed how gummy the linkage was, so I decided to clean it. I couldn't find carb cleaner on my shelf, but the brake cleaner said it didn't do harm to plastics and was designed to degrease/de-gunk. So I sprayed that on the linkage, and a bit on the trottle plate, the engine was off. Well the linkage got cleaner, but it was harder to move, so I lubed it. When I re-assembled the air duct and started it up, the idle was at 1900 RPM and would not come down. I rechecked the linkage and found that if I pushed on it, pushing it down into contact with the idle adjustment screw, all was OK. After verifying the springs were attached and apparently working, I figured a speck of gunk was holding the throttle plate from it's proper resting position. I removed the air hose again, opened the throttle and carefully cleaned around the edges. After re-assembly all seemed OK. In fact it was now idling at 700 RPM (good I thought to myself, it was always at 1,000 before today). I took it out for a test drive and ran into problems. It would stall when I stopped, was hard to start. I got it home and let it sit overnight. This morning the idle wanted to be down at 400 or 500 rpm when cold. I had to goose it to keep it going. When it stalled it was hard to start. After a few highway miles it I pulled into work. The idle speed is OK at 800 RPM, but power is lacking when you accelerate from idle.

Best case this will all work itself out, worst case I'm going to get stuck. Have you ever heard anything like this? Any thoughts, comments or suggestions are greatly appreciated.

Thanks,

John

Submitted by jam@ispwest.com on Thu, 12/16/2004 - 15:26

you're welcome, it happens to the best of us!! I had a feeling the answer was in retracing the steps...(as in forgot to tighten the clamps!!), but yes, that area is extremely sensitive to being air-tight. (no pun intended). There are known fixes for the flap inside the AFM, and for the electronic circuit if it ever goes bad, and they rarely go bad, remember, mine is 20 years old, still ticking, other than the Plug Contacts which get corroded with age causing intermittent symptoms, the AFM is rarely to blame, so I don't think you'll ever have to replace it.

Another related tip: adding a Ground Strap to the O2 Sensor will improve idling and response. This is a subject that is slowly developing, started by people in the know, because as you may know, "the company" added a ground strap to the Oxygen sensor late in the series, but never "recalled" the "others" to retrofit them. I liked the results of the mod so much that I dished out the money and developed a proper copper/braided strap with proper O-Ring connectors for the 1-wire Oxygen sensors. (please note: for 1-wire sensors only, up to 1986 I think, since the 1987 came with 2 or 3 wire sensors depending on their destination). if you are interested, let me know, I'll send some pics. I've sold them to non-believers who turned into born-again faithful about their XJ's which had lost the "spark".

Submitted by johnkenny@avaya.com on Thu, 12/16/2004 - 14:33

J.A.M.,

You were right on target. Before lunch I was reading about the Air Sensor in ALLDATA.com. Did you know that the fuel pump relay runs through this? Inside the air sensor is a flap that moves as more air comes through. If it is not at least moved by 8 degrees, the fuel pump relay is open. In fact the instructions mentioned that you should check the flap for ease of movement. If it sticks, the air fuel ratio will be off, causing the symptoms of low power at low RPM. Unfortuntately the fix is a total replacement of the $300 air sensor. I expected the worse, but hoped for the best and I went out at lunch. The car started nicely, I put it in reverse, it moved 10 feed and died. The car wouldn't start at all! Before I called a tow truck I looked under the bonnet. There was an air leak (I'm being kind to myself - the entire hose fell off) where the convoluted hose attaches to the Air sensor. It was my sloppiness from last night, guess I forgot to tighten the clamp. I reattached it, tightened it up according to your instructions and all is OK now. Its got to be perfectly tight like you said.

BTW, I love the idea of modding the side lights. I know what you mean, this will be much safer.

Thanks again,

John

Submitted by jam@ispwest.com on Thu, 12/16/2004 - 12:12

great instructions for adjusting the buttlerfly plate; I copied them for next summer. "Convoluted" hose, that's the word I was looking for, but I only thought of "bellows", they do look like the Cruise Control "Bellows". In my 13 years with the XJ-6, I have learned that the entire area from the
air intake "Trumpet" all the way back to the butterfly, is a very sensitive area and the slightest adjustment or disassembly becomes a quagmire of symptoms with the idling, I read about these problems every week.

By the way, I modified the static (On or Off) Sidelights in my XJ to blink with the normal Turn Signals, front and back, left and right. Cost? $5.00 in materials and a Saturday. Well worth the improvement in safety, since
the Turn signals in the Series 3 XJ are not visible from the sides of the car. www.jagbits.com has posted my mod in their Tech Library if you are interested in making your sidelights blink.

Happy Holidays!

Submitted by johnkenny@avaya.com on Thu, 12/16/2004 - 10:58

Thanks, That's a good start. I just looked this up re: adjusting the butterfly plate

Remove the elbow and convoluted hose to expose the throttle body.
Loosen the throttle butterfly locknut and stop screw to ensure that the throttle butterfly valve closes fully.
Insert 0.002 in (0.05 mm) feeler gauge between top of valve and housing to hold valve open Fig. 1. .
Set the stop screw to just touch the stop arm and tighten locknut with the feeler in position.
Press the stop arm against the screw and withdraw the feeler.
Seal the threads of the adjusting screws and locknuts using a spot of paint.
Refit the elbow and convoluted hose.
Check the throttle linkage adjustment, operation of the throttle switch and the kickdown switch adjustment.

I bet I get to the bottom of this. Thank you very much.

John

Submitted by jam@ispwest.com on Thu, 12/16/2004 - 10:34

I don't profess to be the almighty expert on this subject, but I ran into the same problem with my '84 after cleaning the intake system, only difference is that I used the proper cleaning product (Carb Intake Cleaner For Fuel Injection), and you say you used Brake Cleaner? yuk, doesn't sound good. Regardless, check and recheck the Vacuum Hoses, particularly under the right front fender (wing) where all the Charcoal Canister hoses are, even if you haven't worked there, and those that cross into the engine compartment from the charcoal canister. Check the Plug at the AFM, it gets "lazy" with corrosion on the contact pins. Check the plug connection at the Cold Start Injector, near the Throttle Intake, check those big 'bellows" hoses for tightness, if the air intake system is not perfectly tight and set, all sorts of strange symptoms pop-up.

If the car was running right before you worked on it, retrace all your steps.