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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.
All else fails, then try a replacement MAF.
MAF got blasted with cleaner. Doesn’t look like the usual hitachi or bosch with the exposed hotwire so not sure how much good it does.
Weird how the car won’t start without the MAF but will run all day long and very driveable when unplugged at idle.
1. Coils
2. You sure you have good coils?
3. Look point 1.
4. Only then look elsewhere.
Only early cars can start with MAF disconnected, later ones do need MAF connected but I wouldn't worry much about that before replacing coils. Even if MAF is slowly failing(they do indeed) a P38 MAF works well and is fairly cheap. A lot of other things than coils can be diagnosed with an OBD scanner. Bit pointless to troubleshoot an x300 without one. Plug one in and check live data. Check if o2 sensors change to close loop and are ok, check temp sensor and MAF at idle and what TPS shows up. All these can be checked in 2 minutes with an OBD scanner that cost $10?
Other than that the only two other things causing idle issues could be an air leak(one of vacuum lines going into manifold disconnected, there are three?) and maybe failing fuel pressure(you can pinch return line temporarily to check that) but again, always go the coil route first, especially if they are of unknown origin.
Originally Posted by xalty
MAF got blasted with cleaner. Doesn’t look like the usual hitachi or bosch with the exposed hotwire so not sure how much good it does(...)
To proper clean MAF, you need to drill out 4 rivets, then pull the main element out and only then spray and clean it gently, then replace rivets with screws.
Last edited by katar83; 07-26-2020 at 05:56 AM.
Reason: added more info.
Alright just pillaged two junked X300s. One was looted pretty hard but I was able to pick up a door check strap and some bulbs. Red one has freshly arrived and still had a MAF and everything else you’d want except exhaust manifolds of course. Anybody need a 10/10 condition center vent?
Got home and plugged it in, noticed a small crack in the rubber MAF to intake coupler but shouldn’t be this significant. Starts up and does a similar crappy idle routine, dips and all. At idle STFTs sit at 25%, unplugging the MAF causes the air pump to immediately run and once it’s off stfts go into the dirt, pegged at -24/-25 stationary and peaks at 3% under load.
Need to compare the flow rates and fuel trims between both MAFs but again they could both be broken.
Originally Posted by katar83
Cause of idle issues on x300 are always:
1. Coils
2. You sure you have good coils?
3. Look point 1.
4. Only then look elsewhere.
Only early cars can start with MAF disconnected, later ones do need MAF connected but I wouldn't worry much about that before replacing coils. Even if MAF is slowly failing(they do indeed) a P38 MAF works well and is fairly cheap. A lot of other things than coils can be diagnosed with an OBD scanner. Bit pointless to troubleshoot an x300 without one. Plug one in and check live data. Check if o2 sensors change to close loop and are ok, check temp sensor and MAF at idle and what TPS shows up. All these can be checked in 2 minutes with an OBD scanner that cost $10?
Other than that the only two other things causing idle issues could be an air leak(one of vacuum lines going into manifold disconnected, there are three?) and maybe failing fuel pressure(you can pinch return line temporarily to check that) but again, always go the coil route first, especially if they are of unknown origin.
I’m using an ELM to monitor most of the data. I’ve just picked up an uncracked original Lucas/Diamond coil, gonna go one by one. Still, the fact it runs super extra smooth in failsafe mode points to a mixture problem rather than a coil.
I’m using an ELM to monitor most of the data. I’ve just picked up an uncracked original Lucas/Diamond coil, gonna go one by one. Still, the fact it runs super extra smooth in failsafe mode points to a mixture problem rather than a coil.
I've lost count how many times I went through the same logic when troubleshooting X300, only to be proven wrong majority of times, when replacing coils fixed everything idle related
I'm not saying that this is the case with yours but I would never trust an unknown coils in an x300 anymore. I've swapped way too many things on my x300 cars chasing idle issues, so now always have a QYL coil set ready to swap, before going any further. Sadly one coil might not be enough to troubleshoot it either.
By the way you wont be able to proper test MAF with an OBD as that's one thing that is not properly setup in a Jag OBD. Think it shows 0.02 at idle normally.
Alright did some testing. With either MAF plugged in STFTs are around 25% at idle or and immediately drop negative when the stumble happens. The higher the load/throttle the closer it gets to zero.
Unplugged idle STFTs are pegged around -25 and approach zero or slightly positive under load. So currently I have the choice between a mega rich or leaned out idle.
.
By the way you wont be able to proper test MAF with an OBD as that's one thing that is not properly setup in a Jag OBD. Think it shows 0.02 at idle normally.
The Mass Air Flow as a engineering rule of thump is considered to be 1.0 gram / sec for each liter of dis[lacement at 650 RPM
The higher idle of the X300 would make you bump up the 4.0 a bit
The ELM - 327 from reading of postings can be off by a factor of 10 and even 100 by a software error
So given this you can reexamine your MAF data and it may make sense
As you increase the speed of the engine ( not necessarily the load ) you increase the replenishing supply of vacuum to overcome a leak being a factor so STFT coming into range target of 0.0 is common on throttle up
The target of 0.0 is not always achieved so wavering + or - 3.0 common
As you increase the speed of the engine ( not necessarily the load ) you increase the replenishing supply of vacuum to overcome a leak being a factor so STFT coming into range target of 0.0 is common
The target of 0.0 is not always achieved so wavering + or - 3.0 common
Regardless this car is majorly overfuelled at low RPM with the MAF plugged in. O2 pegged at 1V and STFTs in the 20s. MAF out and the car’s -20s, lean but still nowhere lean enough to stall.
The O2 sensors on the X300 are different as they are platinum that generate a O2 concentration reactive resistance that a reference 5.0 volts goes through and returned to the ECU
This return is in the range of 3.5 volts
The ELM reader can not always discern this difference and as a default give you data based on the Zirconium technology as well as the confusion of the lambda number needing to be in the target value of 1.0
Fuel injector cleaner in the tank ? Techron
Cracked exhaust manifolds ?
The performance of the fuel injectors are very critical at the idle speed short pulsewidths
Exhaust manifolds are in great shape. Need surefire ways to force open loop, even with the temp sensor out the car appears to still be running closed. These O2s sure look like the platinum NTKs\Bosch 13021 used on everything, I remember splicing one in on a Range Rover.
I’ll try some techron this fill up and see what happens, if i’m lucky it could be a weak or clogged injector.
Bosch 13021 seems to be the wrong part # in my head but then it could be one that you install your own electrical connector or extra long wire length
Bosch 13089 comes to mind as a ready to install , connector ready, if you were to buy a new one
With the coolant temp sensor calibration chart showing high resistance equals a low coolant temp , removing the connector would mimic a cold coolant and open loop
bridging the sensor with a low value resistor should mimic a hot coolant as long as that resistor is not seen as " out of range " from what the ECU expects
A direct short across the connector puts the ECU at risk of damage
O2 sensor heaters ? as they are needed to get the sensor to operating temp before they will even operate correctly at idle exhaust gas temps
There is 1 fuse for all 4 sensors , # 14 / 10 amp Right engine fuse box
The 2 small ground studs on the rear firewall clean as these are the shields on the 4 return signal wires to the ECU
On mine I found alot of corrosion on the rear sensor connectors
Someone found the connector pairs crossed and this effects idle
On the ECU side of the O2 sensor connectors 3 wires are marked the same but the 4th wire is different
The Papa Indy 61 connector has a history of corroding and subject of a TSB , look for pin 12 of the black connector ( White / Green ) wire
From reading some people have sent off or self deep cleaned the injectors after removal , there is a basket filter inline in each injector
Bosch 13021 seems to be the wrong part # in my head but then it could be one that you install your own electrical connector or extra long wire length
Bosch 13089 comes to mind as a ready to install , connector ready, if you were to buy a new one
13021 is for an 80s Nissan Sentra, I'd splice it in since they're like 20 bucks.
PI61 was a little crispy with dried grease, cleaning both upstream connectors, it and PI1 were identical and look different from the white connector block I see in the photo? Was there a mid production change to take care of this?
Plot twist: EMS has been repaired at some point. Every ground and connector in this area is squeaky clean and dry as a bone. Could explain the random LHM light that came on the drive before all this. Back to the junkyard we go
There is a match between the original ECU " orientation or factory setting " and the original TPS mounting position as it relates to the throttle closed position sensor value
The hunt begins to get the 2 to match again with the ECU orientation fixed as the adjustment of it is special Jaguar equipment dependent
But before opening up a new can of worms the MAF responce needs to be resolved
Don't acquire another ECU but verify the candidates part #s
There is a match between the original ECU " orientation or factory setting " and the original TPS mounting position as it relates to the throttle closed position sensor value
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Apparently these guys have a legendary reputation of scamming and not actually rebuilding stuff, who knows.
I’d take the ECU out of the red car I took a TPS from if that would allow me to skip the syncing process. JLR dealers should still be able to run adaptations via IDS right?
07-25-2020, 09:49 AM
