DaytonaRS7
Full Access Member
the stumble at idle would make me think vacuum leak.
MAF sensor and O2 sensor bad?
- Thread starter Michael Gain
- Start date
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Michael Gain
Full Access Member
I would assume the same, but it is not consistent. I do not experience on my drive to work, but do on my way to lunch and drive home. Seems engine temp dependent (maybe vacuum leak present once expansion occurs), but when it does not bog on an incline, that points me towards the fuel tank (maybe). My DMTL pump runs for a minute or two after shut down on occasion. Not sure if that matters for this symptom, but I still need to finish troubleshooting that as well. I plan to take a good look at the evap bits while the tank is removed.
jlglr4
Full Access Member
Someone on landroverforums is having what appears to be the same problem. He’s tried to get on this forum, but can’t seem to get a response from the admin.
I’ve been trying to brainstorm with him and just noticed yesterday that this might be the same problem you’re having. 2015 LR4 with close to 100K as I recall. Intermittent surging rough idle and his STFT and o2 readings bounce around from rich to lean when he’s having the problem. o2 seems to read rich when he’s not having the surging idle.
I don’t have any new ideas yet, just thought I’d mention it.
https://landroverforums.com/forum/lr4-38/daily-intermittent-rhythmic-engine-shudder-104587/
I’ve been trying to brainstorm with him and just noticed yesterday that this might be the same problem you’re having. 2015 LR4 with close to 100K as I recall. Intermittent surging rough idle and his STFT and o2 readings bounce around from rich to lean when he’s having the problem. o2 seems to read rich when he’s not having the surging idle.
I don’t have any new ideas yet, just thought I’d mention it.
https://landroverforums.com/forum/lr4-38/daily-intermittent-rhythmic-engine-shudder-104587/
jlglr4
Full Access Member
Just another thought - could the fuel control be operating in open loop for some reason - maybe a bad coolant temp sensor? I would think you’d see a code, but maybe it’s cutting in and out enough that no code is popping up.
Michael Gain
Full Access Member
Coincidentally, i have been watching that thread lol. It's a weird frustrating issue. I thought I could correlate it to the rear a.c., but that was a fluke. I'll drop a note to him in the gas tank parts improves the condition.
I will also look at the coolant temp sensor. Even if just checking the voltage. The rear sensor is new with the rear crossover, but I did not replace the front sensor with the thermostat... unless it is built into the thermostat.
I am with Daytona at this point. I think it is a weird, conditions based vacuum leak... or the throttle body... or a million other things.
Do you have one of those propane **** torches? If it is a vacuum leak, you might find it by opening that up a little (not lit, obviously) and moving it around the engine compartment to see if there's an area where the idle smooths out or picks up.
Michael Gain
Full Access Member
Good suggestion. I have a smoke tester. But, it showed no leak the last time I tested the intake and vacuum system. Granted, I tested on a cold engine. I may try again on a warm engine to see if expansion is creaking a leak.
jlglr4
Full Access Member
To answer the question on the temp sensor, the one in the front is not part of the t-stat. It is sold as part of the lower radiator hose just below the t-stat, but I think it is replaceable separately. I’m not sure how the ECM uses the two signals together in the fuel control system, but I believe both play a role.
I’m also trying to think about the possible relationship to the DTML pump. As I understand the system, the DTML pump pressurizes the tank, which is connected to the purge cannister, which is in turn connected to the purge valve. When the purge valve opens, it vents the cannister to the air intake. So, if there were a leak in the evap system, it could create a vacuum leak in the engine only when the purge valve was open (or if the purge valve was faulty). I recall someone in these forums reporting that a garage discovered a leak in the DTML with a smoke tester. Can’t remember if it was causing a vacuum leak, and can’t find the post.
I’m also trying to think about the possible relationship to the DTML pump. As I understand the system, the DTML pump pressurizes the tank, which is connected to the purge cannister, which is in turn connected to the purge valve. When the purge valve opens, it vents the cannister to the air intake. So, if there were a leak in the evap system, it could create a vacuum leak in the engine only when the purge valve was open (or if the purge valve was faulty). I recall someone in these forums reporting that a garage discovered a leak in the DTML with a smoke tester. Can’t remember if it was causing a vacuum leak, and can’t find the post.
Michael Gain
Full Access Member
To be honest, I replaced the fuel purge valve in one of our LR4s, but I do not remember which one... It will throw a code if faulty though.
I may remove it and push smoke back through the fuel purge valve line; just to see what happens
jlglr4
Full Access Member
What if you just pull it off (and plug the connection to the throttle body) and see if it fixes the idle? I agree - you should be seeing a code, but ... who knows. The guy on the other forum just said he thinks he can hear a clicking from what I assume is the purge line. He’s also reporting pressure in his tank, which makes me think of your DMTL pump.
