Turn on the AM stereo and run the engine noticing a background hum varies with engine RPM

Compare to AM background noise with the engine not running and stereo being powered by pure battery DC electricity

Your data on the STFT swings back and forth like sharks teeth

The off scale of 24.2 has been observed by others

MAF X 100 ?

Are the readings at constant throttle ( idle or other ) ?

 

Ran some gumout regane last fill up, been running with ECTS unplugged. STFT is totally pegged at +24.22 at idle, no more shark dips.

Idle is pretty smooth for first 30ish minutes of operation and progressively gets slightly rougher, but again no dips.

MAF x 100 sounds about right. the Range Rover P38 guide says 20-25 kg/h is normal range at idle.

 

plugged ECTS back in when hot, accurate 188f reading car immediately started doing the usual stumbling routine. unplug it again and idles good enough

 

By unplugging the ECTS the resistance value is infinitely high or out of expected range so the ECU probably rejects the data / variable and reverts to a different , less then optimal set of data maps minus a ECTS data / variable

This would be different then a " excepted " value in which case would mimic a cold coolant temp tp go to open loop mode

In my opinion you would be better to resolve your idle in the closed loop mode using the O2 sensors and full engine regulation

Without knowing that you were reading a properly operating O2 sensor system in your example you can swap the front 2 O2 sensors to the rear

All 4 are the same length and connector no key

Eesier said then done

On the X300 4 o2 sensor setup the rear sensors regulate the engine and the front determains catalytic converter efficiency error CEL code

swap one pair at a time while the ECU learns of it's new perimeters and then swap the second pair less the chance the ECU would get lost by the change

Rear firewall small ground post clean , 2 , these are the shield wires to the sensitive O2 sensor return wires to the ECU

Rear O2 sensor connectors clean ?

crush washers on the O2 sensor mounting boss , 12 or 14 mm different then the spark plugs . The position of the sensor in the gas stream seams to make a difference

You can source some from a cheap copper 12 mm spark plug

Cap the vacuum hose fitting under the intake manifold around cylinder 2

cap the banjo fitting to the brake boost cylinder

 

Don’t you just love it when the car finally decides to throw a code. P13B0 and B30F4 also came out to visit.

 

AM radio test ?

Trust me , this is my first Jaguar so I'm an expert in the field

 

can’t pick up on static tone too well, sounds all the same to me

 

It would be more of a pulsing or swirling noise that varies with RPM

The source of the pulse if present would be from the alternator diode package or the separate noise suppressor that further smooths out the AC waves to be more flat pure DC electricity

Coils can induce a AC component into the electrical system including the power to the ELM reader

The engine block large ground helps this in theory

The CEL codes are not perfect but odd they would show up now which should relate to the confidence the codes are valid information

Also your data is not stable or on one side of expected or the other

The codes can be found on page X of the Jaguar 801s document

 

This looks very reminiscent of a problem I had, with excessive fuel trim at low RPM. The problem turned out to be a leak at the exhaust manifolds to downpipe connection. Counterintuitively, this was allowing oxygen to be sucked IN between exhaust gas pulses, confusing the O2 sensors into thinking the engine was running lean, and causing the ECU to enrich the mixture. Remaking the joint solved the problem.

 

I have the part # for the donut gasket ( 2 ) downstairs in the garage someone helped me out with

Easy to obtain from the local auto parts store

60 mm in size

Look for a clean unbent not damaged flair on the downpipe

The studs get in the way

 

Connection looks tight, gonna dump some seafoam in and see if that’ll show a leak.

First though it’s time to load up the parts cannon and get some coils, misfire code is enough suspicion at this point.

 

QYL on Amazon seem to work well for others. At the price point, for what you need, I'd say they were perfect.

 

That’s what I ordered.

They jacked up the price on the made in japan eurospares, complete no-go.

 

One thing to consider with your ELM - 327 reader and what information it gives you is the difference in a bluetooth data link and the wired USB port version reception

The data it receives refresh rate is slower with the bluetooth as the databus communication ( from what I have discerned from reading ) and this is critical with reading what your O2 sensor system is doing as it oscillates by design to force the ECU to recalculate the injector pulsewidths ( fuel trim ) as the ECU does not have a heartbeat monitor

This does not instill confidence in what the ELM - 327 does or does not tell you but is a variable of consideration in troubleshooting

 

Eurospares are junk. (Eurospare anything tends to be poor)

Diamond brand is the Made In Japan you are looking for.

QYL is reportedly a good substitute!

 

6 new QYLs in, mega rich idle and stumble problem persists, P0300 still stored. MAF out resolves idle, coolant temp sensor out smooths it out for a while.

 

With the MAF connector installed does the middle wire on the connector read 1.2 volts DC at the correct idle speed ?

This is a known value that happens to be in your area of interest .of idle

MAF part # ? , Lucas 20AM or something

 

Alright a little update. Spoke a little too soon when I changed coils with a hot engine, after the next cold start it started running smoother than ever and has been like that since.

Marriage falling apart? Replace all 6 coils

Dog won’t behave? Replace all 6 coils

Bleeding out from a gunshot wound? Replace all 6 coils

IRS going after you for tax evasion? Replace all 6 coils

 

Sorry about your dog

 

Not quite the end of the story. Running smooth but dips in P returned this drive a while after warmup.

Noticed my IAT readout is very high at 150F+, weird. Pulling it makes it report 361F with no change.