Limp Mode after long idle (1 Viewer)

[trudd]

'09 LX, 164k miles, I've owned it for 2 years. Southern truck, no rust.

Just experienced the same thing for the 3rd time this year - the car enters into limp mode after idling for a decent amount of time... say, at least 30 minutes. We don't often let the car idle that long, but when baby falls asleep, there's not much you can do!

Observations:

• the one time this happened while I was in the car, I noticed the RPM needle bouncing from ~600-800rpms about a minute before triggering limp mode.
• the car starts right back up without hesitation
  • Today I noticed that the temp gauge was slightly higher than normal after restarting the car. It very quickly bounced back into the middle after restarting. This is new and the temp has not spiked
• No CEL or stored codes that I've found
• I have a known valley plate leak, but keep the coolant reservoir topped off

I'm also currently chasing what I think is a separate issue. I have a frustrating vibration at almost all speeds. I'd call it intermittent, but it happens during 80% of driving. I've done globes, AHC fluid, replaced u joints, balanced tires, checked bushings... Only adding this here as context, though I'm not sure it's related.

What should I be digging into that would cause the engine to go into limp mode while idling, but doesn't trigger CEL?

 

[TeCKis300]

'09 LX, 164k miles, I've owned it for 2 years. Southern truck, no rust.

Just experienced the same thing for the 3rd time this year - the car enters into limp mode after idling for a decent amount of time... say, at least 30 minutes. We don't often let the car idle that long, but when baby falls asleep, there's not much you can do!

Observations:

• the one time this happened while I was in the car, I noticed the RPM needle bouncing from ~600-800rpms about a minute before triggering limp mode.
• the car starts right back up without hesitation
  • Today I noticed that the temp gauge was slightly higher than normal after restarting the car. It very quickly bounced back into the middle after restarting. This is new and the temp has not spiked
• No CEL or stored codes that I've found
• I have a known valley plate leak, but keep the coolant reservoir topped off

I'm also currently chasing what I think is a separate issue. I have a frustrating vibration at almost all speeds. I'd call it intermittent, but it happens during 80% of driving. I've done globes, AHC fluid, replaced u joints, balanced tires, checked bushings... Only adding this here as context, though I'm not sure it's related.

What should I be digging into that would cause the engine to go into limp mode while idling, but doesn't trigger CEL?

Get an OBD-II reader and pull codes. If the reader is able to, check long term (LT) fuel trims.

If I had to guess, it sounds like the fuel pump. Could also be the ignition system, plugs or ignitor.

I had issues with my fuel pump on my '09 around that mileage

P0171: System too Lean (Fuel Trim)

Working through this and could use the hive minds support. P0171: System too Lean (Fuel Trim). Also P0300: Random/mulitple Cylinder misfire detected. Multiple specific cylinder misfires P030x. Symptoms: In diagnostics after getting home. LT fuel trim on both banks at idle are high. +15 and...

forum.ih8mud.com

 

[trudd]

I read through your thread. Great info.

Tried to pull codes. There are no current or historical codes associated with this.

I’m a fuel system noob - am I pulling in the right data on OBD Fusion? Any other useful data points to add to this dashboard?

I snapped these while parked. Engine was not quite up to operating temps. I will be road-tripping later and can snap again after a few hours of operation.

 

[bloc]

I’m no expert but those long terms seem excessive.

I’d monitor how those change after a long drive.

 

[trudd]

I’m no expert but those long terms seem excessive.

I’d monitor how those change after a long drive.

I’ll report back tonight.

I went ahead and cleaned the MAF for the first time ive owned it (28k miles). PCV was replaced when I bought it. No dealership maintenance history when it comes to fuel pump, plugs, coils, that I can recall.

 

[TheComedian]

This 600-800 idle (in my case more 500-700 if i dont pish the high idle button) comes normaly from the AC. Was the AC on when you had the car in idle?
Should be stable low if you turn it off. Thats a normal behavior.

 

[trudd]

This 600-800 idle (in my case more 500-700 if i dont pish the high idle button) comes normaly from the AC. Was the AC on when you had the car in idle?
Should be stable low if you turn it off. Thats a normal behavior.

AC was on in all these cases. Outside temp ranged from low 80s the first 2 occurrences, to 102° yesterday

 

[TheComedian]

AC was on in all these cases. Outside temp ranged from low 80s the first 2 occurrences, to 102° yesterday

The AC in that case doesn’t care that much about the temp it has to cool. Just taking a bit more power every now and then and the engine idles a bit up.
Try it again without. You’ll notice the difference in the idle

 

[TeCKis300]

I read through your thread. Great info.

Tried to pull codes. There are no current or historical codes associated with this.

I’m a fuel system noob - am I pulling in the right data on OBD Fusion? Any other useful data points to add to this dashboard?

I snapped these while parked. Engine was not quite up to operating temps. I will be road-tripping later and can snap again after a few hours of operation.

View attachment 3363381

View attachment 3363382

You're looking at the right things. Pull a data point when the car is hot. If it's when it's stumbling, even better. At idle and at speed, i.e. freeway.

Usually when there's ignition problems, there's more likely to be CELs. The fact that you're not finding any would make me suspect more that it's a fuel issue.

 

[trudd]

Here are two values from 240 miles of driving today. Long term fuel trims fluctuated like crazy when I would left off the gas at highway speeds. Both banks would hit 12.5% plus.

The first pic is the general average at most pedal positions of highway driving. The second pic is my in P and idling after 180 miles of driving (car had not been turned off).

 

[bloc]

This isn't an informed opinion as I've never watched LTFTs while driving, but based on my understanding of how they work it is interesting they fluctuate like crazy on coast. Still, it seems improbable the underlying ECU code is faulty somehow.

 

[trudd]

Yeah I struggled to truly understand the calculation of those Short- versus Long-term trims, knowing nothing about fuel trims to begin with.

I remember reading that the ECU won't throw a misfire code until multiple occurrences. Wonder what other issues are subject to the same logic - IE, no CEL code, but a significant enough event that the engine needs to protect itself.

My wife noticed it this latest time. We had a video monitor on the baby so he could catch some extra Z's. When my wife saw the monitor she said it was shaking a lot, as if somebody was rocking the car. Must've been a helluva limp mode.

 

[TeCKis300]

That looks like enough trim that I would definitely look into fuel pressure as the next step.

As you're finding, trims are not singular. They are a map of values against load and rpm (and potentially more). They really only have meaning on throttle. Coasting closes the throttle body and fuel injectors so trims aren't as relevant.

 

[trudd]

That looks like enough trim that I would definitely look into fuel pressure as the next step.

As you're finding, trims are not singular. They are a map of values against load and rpm (and potentially more). They really only have meaning on throttle. Coasting closes the throttle body and fuel injectors so trims aren't as relevant.

Gotcha. Guess it's time to learn how to do a pressure test!

 

[bloc]

Also of note.. it's only 50% odds but if a fuel pump is crapping out your fuel trims will always be positive.

 

[trudd]

Small development, maybe. I changed the spark plugs today (possibly the first time they've been changed in 169k miles). That project went well.

After starting back up for the first time, I let it idle for a bit and then noticed a clicking sound accompanied by the same RPM fluctuation that has preceded Limp Mode in the past. This was a matter of minutes after restarting. I cycled off the AC and the clicking sound went away. Cycled back on, and then found the AC clutch clicking on and off very quickly. RPM fluctuations are not captured in this video:



Because of this thread, I've long suspected I was slightly low on freon, since my rear AC runs warm while both front AC and cool box both work fine. I grabbed a gauge from a old DIY Freon Recharge kit and pulled this pressure at 104º ambient temperature. I have never recharged freon on this car and am kind of wary to do so.

Questions

• does anyone know low/hi AC pressures for the 200 series? I've only found it for the 100 series here and cannot find in my owners manual
• is it safe to assume there is correlation between the AC compressor cycling on/off and my rear AC blowing warm? If 200 series are the same as the 100 series numbers I posted above, my low side should be 42-55psi.
  • I don't want to DIY recharge my AC system until confirming 200 series low pressure numbers
• Any chance this is somehow related to my initial limp mode issue?

 

[bloc]

Small development, maybe. I changed the spark plugs today (possibly the first time they've been changed in 169k miles). That project went well.

After starting back up for the first time, I let it idle for a bit and then noticed a clicking sound accompanied by the same RPM fluctuation that has preceded Limp Mode in the past. This was a matter of minutes after restarting. I cycled off the AC and the clicking sound went away. Cycled back on, and then found the AC clutch clicking on and off very quickly. RPM fluctuations are not captured in this video:



Because of this thread, I've long suspected I was slightly low on freon, since my rear AC runs warm while both front AC and cool box both work fine. I grabbed a gauge from a old DIY Freon Recharge kit and pulled this pressure at 104º ambient temperature. I have never recharged freon on this car and am kind of wary to do so.

View attachment 3375115

Questions

• does anyone know low/hi AC pressures for the 200 series? I've only found it for the 100 series here and cannot find in my owners manual
• is it safe to assume there is correlation between the AC compressor cycling on/off and my rear AC blowing warm? If 200 series are the same as the 100 series numbers I posted above, my low side should be 42-55psi.
  • I don't want to DIY recharge my AC system until confirming 200 series low pressure numbers
• Any chance this is somehow related to my initial limp mode issue?

Call around and get quotes on AC shops evacuating and recharging the system. You can go by pressure but the best method for us is to go by refrigerant mass. I use that method when charging mine but you must drain the whole system and pull a vacuum first.

Otherwise on the pressures I’d need to consult the FSM but don’t have access to that right now.

I do think you are on the right path.. the compressor should not be cycling that often and your front and rear AC should be able to blow ice cold. I’m not sure how it would contribute to a limp mode but it is something wrong and everything is integrated these days. Might as well address it.