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Having a minor stumbling issue, only in P. Previously had some issues in D but seemingly resolved by disconnecting the coolant temp sensor. No codes as of current.
When unplugged idle drops from usual 800ish to 600 and recovers quickly, occurs maybe once or twice a minute. No issues in drive except turning on AC drops idle by like 50rpm which is unusual but not sure if behaves like that normally.
Got trans connector out with no issue, didn’t even have to lift the car. Nice and clean even before I sprayed it down.
Took out throttle body, TPS, IACV etc. All a little dirty but nothing to write home about. Don’t think any are the culprit as the car idles at the correct RPM but has progressed to an obvious miss in P and in D.
The aft most coil connection has a history of not being fully engaged
run your finger on the back edge of the valve cover and feel for the gasket not being in place , there is a D shaped cutout that doesn't stay in place
The EVAP and EGR valve should be closed at idle and the EVAP can be tested with a 9 volt battery to feel it click , EGR can can bind and be cleaned
The coil tester is in the back room of O'Reilys auto parts stores , call first as all stores don't have them and you'll have to run the test yourself as they're not up to speed
Bring heavy gloves and the Jaguar X300 coil adapter # is not on the chart because it's special
Last edited by Parker 2; Jul 19, 2020 at 09:24 PM.
Plugged in the ELM, no codes read. TPS sweeps from 11% at idle to 80% WOT with no real issue. LTFT pegged at -4%, obviously running rich. Coolant temperature sensor reports accurately, right at 185F.
With ICV in the car idles at about 700 in P and 580ish under load. when ICV is removed in position 2 it’ll idle at 900 and 700 respectively. Seems like it’s also doing its job, but again it’s still rough.
- 4 % not bad as 0 % is target and varies as it settles down in engine range variances . = or - 3 % seams to be the norm from reading as nothing is perfect in the ECU calculations
Difference between LTFT and STFT ?
EGR error signal ( on the ELM - 327 ) as the X300 has a EGR position sensor vs. command but not a inlet air control valve position sensor
The EGR should be closed at Idle along with the EVAP valve
IAV position 2 ?
As the IAV stepper motor windings
Black ECU connector
Last edited by Parker 2; Jul 21, 2020 at 10:26 PM.
I had a mysterious dip in idle....every 32 seconds. With AC on it could go as far as stalling my engine when I was at a stop light, although most of the time, it was hardly noticeable.
Long story short? It was the intake manifold gasket. Hell of a time finding that leak!
If you’re planning on changing that, make sure you change the ******* hose while you’re in there.
The 11 % TPS at idle is normal , this probably because the IAV is slightly open and they take this into account with 0 % being both air paths closed completely
There is a mechanical idle stop adjustment that I'm not aware of and missed when I had my TB off for cleaning
The coolant rail under the intake manifold has a history of the coolant gasket ( item # 4 ) leaking so it's one of those things while you are there if you have to look at the intake manifold gasket
Mine was missing one of the vacuum hoses to the EVAP
Valve cover gasket bulging out from sealing on the back edge ? There is 2 D shaped protrusions in the seal to cover for a machine cut out in the back . This does not always seal even if the D shape is placed properly . Form a gasket in the corners of the D shape . Gasket age ?
Early cam number that had problems idling where they changed the cam to address it in a TSB ? Stamp on engine casting by the X ?
The number stamped on the cam is a casting number not related to the change in upgraded Cams
Alright another update. First time this issue came up I tried unplugging the MAF when car was off and car refused to start. This time I pulled the MAF while car was running. Much smoother, no more idle drop.
I know the on the 14CUX and probably the jag 15CU there’s multiple failsafe fuel maps. One that ignores oxygen sensors and also one that bypasses the MAF and fuels based on throttle opening. Not sure how do they do it on GEMS.
Looks like the next voyage is to find an AJ16 MAF in a yard, or worst case I’ll lift it off a GEMS Range Rover/Discovery.
The MAF on the center wire should read 1.2 volts DC at the correct idle speed, that will tell you it is alive
The normally aspirated and supercharged MAF part #s are different
On mine i found the TPS connector lock clip missing so the connector was sitting on there and not snug
The TPS on middle wire at the idle stop should read 0.60 + or - 0.02 volts DC . Key to the on position but engine not needed to be running . This measurement is critical and should be accurate . Do not adjust until you have a understanding of how tinkering with can go wrong
This TPS center wire ( Green / Yellow ) goes over the top of the fuel rail where you can nick some insulation
Put in 6 new lawnmower spark plugs. Old ones don’t look too terrible so obviously didn’t do anything.
I thought they were tractor spark plugs. Or did you mean a riding lawn mower?
My dear old sixes used to begin their intermittent stalling sequence at or around 20,000 miles on the plugs. New ones always seemed to cure it (or a new CKPS)! Very easy to rule out that possibility, well done.
Oh my goodness Parker, I thought I was looking at a Periodic Table of the Elements. It is really a Jaguar table of Very Important Connectors. More useful here.
I think the slightly rich running engine would point the finger in the direction of a faulty sensor. In all cases, my engine ran lean with vacuum leaks.
The do make an off the shelf MAF cleaner spray you can try at Advance Auto, or the like.
I would also try playing with the harness at the MAF. Sometimes they age and as you move the wires around at the plug, you can get a result.
Lastly, sometimes then pins into the harness don’t make a solid connection any more. A slight twist to the three pins will resolve that. Of course a shot of electrical contact cleaner will also help.
Idle checklist
