2001 4.0 shudder when turning off engine hot

my 2001 xj 4.0 has this very annoying symptom, here's is a quick background of the car.

- manual transmission, 30K miles, engine in excellent mechanical condition.
- have intake with K&N filter, 62mm throttle body, flow daddy header, brola muffler and high flow cat, thermally insulated intake and 180 thermostat.


what happens is that in general when i shut off the engine ( even with stock components ) , the engine dies with a shudder. a sudden irregular shake that last for a 1 sec after the ignition is cut off.

The condition increases significantly when the car is hot, after lots of stop and go driving, with the e fan on, i shut the engine and there is a huge shake with a metallic clunking noise as if something rotating loose is slowing down. very annoying noise last for 1 to 2 sec.

I have no error codes or any worn engine mounts or sensors or irregular running conditions.

idle is very smooth but accompanied with occasional minor hiccups only felt when looking at the engine running.

the other observation is that idle air/fuel ratio is between 14.5 to 15 ( wideband afr gauge )

The only thing i notice is a HUGE reduction in power and increased harshness when i turn the AC on. Although the AC itself is working very well.

what i tried and all didn't work is:

- 2 times sea foam
- cleaning injectors
-changing injectors temporarily to 24lb/hr units
- new and properly gapped spark-plugs
- heat shielding the intake manifold
- checking for vacum leaks


I dont know if this is related to the common heat soak issue or is what called engine diesiling or over-run.

appreciate some thoughts on this

Your idle AFR is correct.

Is the engine rotating while it is making this sound? If not, I would look at items that can rotate after the engine stops.

Possible bad fan clutch?

I have a similar problem on my 99 minus the power loss. I found that it was the electric fan on mine. It looks smooth when it is turning, but when I removed and inspected it, I found that the center of it had melted and deformed a bit. The big key that led me to looking at it was that it took a couple seconds after turning off the engine before it stopped. If that is the problem you have, find an oem replacement even if used. I tried 2 replacements (one from NAPA and one from autozone) and they were both worse than the melted stock fan.

the puzzling thing is that it happens also when the e fan is off. it has something to do with heat, cuz if I turn the car off while temp is still in the 1st 1/3 of the gauage up to 180 F, the engine shuts of relatively normal, just a slight shake. but when its hot, it is really severe, can feel through the transmission lever and the whole car.

is it normal for the clutch fan to turn at nearly the same engine speed during cold starts?, pulling out of my drive way in the morning, the clutch fan always roars .

The clutch fan roar first thing in the morning is normal.