Temp loss of throttle when cold

[jmonica]

Hi. When I start my car in the morning, I drive about 30 secs and then the throttle goes dead neaa asking I depress the pedal and it doesn't react. It feels like the car is about to die but it doesn't.

After about ten seconds, it starts running normal and I continue on my way.

It's been doing this consistently for a few months. It does it once web. The engine is cold but today it did it once then about 20 seconds later did it a second time so I'm sure it's going to cause another AAA tow at some point.

No codes beyond the perpetual vent valve circuit code that I've had for a year. I think it's p0449.

I would think I'd have a code if it was something like the TPS or Cam sensor but I don't. Any thoughts?

Thank You

 

[Mooseman]

Do you still have an electro-viscous fan clutch? If so, try unplugging it to see if the problem goes away. Just monitor your temps while unplugged and you will get a code for it. Sometimes when it goes bad, it also affects the throttle circuit's 5V reference but usually throws a code for it.

What's the status of the SAIS? Is it still functional or deleted? Maybe the valve leaks when it tries to shut off. It only comes on when cold to help warm up the cat so it may be throwing off the O2 sensor.

Have you checked the ignition switch? Do the gauges in the cluster go dead? When it does this, have you tried shutting it off and restarting? For any electrical gremlins, I always give the ignition switch the stink eye.

I would be setting up an Elm327 adapter with the Torque app to monitor and record the APP (accelerator pedal) and throttle desired and actual positions to see if any drop out. I would also record PCM voltages, ignition switch voltages (or power moding), RPM, O2 sensors, MAF, MAP. If it's available, I would also add the SAIS valve status.

With issues like this, you're flying blind without the ability to monitor and record data.

 

[mrrsm]

Checking in the 2006 GMC Envoy Owner's Manual ...On Page 3-47 shows what the "Reduced Engine Power" Warning Light looks like. Any chance this showed up even temporarily around the same time that the APP issue occurred?



The conditions for REP to occur involve the PCM programming hedging its bets against ANY possible problems of having a "Runaway Engine" happening and causing any lurching or acceleration of the SUV then becoming "Out Of Control".

The GM 4.2L LL8 Motor regulates how much POWER it produces by controlling how much AIR is ingested... NOT how much FUEL is expressed into the cylinders by the EFIs.

As long as More Air comes in... the Engine with dump in enough Fuel to accommodate a Stoichiometric Balance of 14.7:1.

The PCM tries to Reconcile the "Driver's Intent" with the actual speed of the vehicle and whether or not the Brake Pedal is being depressed and thus they are also part of this Safety Calculus,

The components that provide inputs for this Safety Calculus are:

(1) The (Dirty or Stuck Butterfly Plate) Throttle Body.
(2) The APP "Gas Pedal" Module (Dual Signal issues).
(3) The (Dirty) MAF Sensor.
(4) The VSS Module (Actual Vehicle Motion)
(5) The Brake Pedal Sensor (Depressed or Released)
(6) A (Clogged) CAT

 

[jmonica]

Checking in the 2006 GMC Envoy Owner's Manual ...On Page 3-47 shows what the "Reduced Engine Power" Warning Light looks like. Any chance this showed up even temporarily around the same time that the APP issue occurred?

View attachment 117123

The conditions for REP to occur involve the PCM programming hedging its bets against ANY possible problems of having a "Runaway Engine" happening and causing any lurching or acceleration of the SUV then becoming "Out Of Control".

The GM 4.2L LL8 Motor regulates how much POWER it produces by controlling how much AIR is ingested... NOT how much FUEL is expressed into the cylinders by the EFIs.

As long as More Air comes in... the Engine with dump in enough Fuel to accommodate a Stoichiometric Balance of 14.7:1.

The PCM tries to Reconcile the "Driver's Intent" with the actual speed of the vehicle and whether or not the Brake Pedal is being depressed and thus they are also part of this Safety Calculus,

The components that provide inputs for this Safety Calculus are:

(1) The (Dirty or Stuck Butterfly Plate) Throttle Body.
(2) The APP "Gas Pedal" Module (Dual Signal issues).
(3) The (Dirty) MAF Sensor.
(4) The VSS Module (Actual Vehicle Motion)
(5) The Brake Pedal Sensor (Depressed or Released)
(6) A (Clogged) CAT

I do not see the Reduced Engine Power indicator appear when this happens. Thank You!

 

[jmonica]

Do you still have an electro-viscous fan clutch? If so, try unplugging it to see if the problem goes away. Just monitor your temps while unplugged and you will get a code for it. Sometimes when it goes bad, it also affects the throttle circuit's 5V reference but usually throws a code for it.

What's the status of the SAIS? Is it still functional or deleted? Maybe the valve leaks when it tries to shut off. It only comes on when cold to help warm up the cat so it may be throwing off the O2 sensor.

Have you checked the ignition switch? Do the gauges in the cluster go dead? When it does this, have you tried shutting it off and restarting? For any electrical gremlins, I always give the ignition switch the stink eye.

I would be setting up an Elm327 adapter with the Torque app to monitor and record the APP (accelerator pedal) and throttle desired and actual positions to see if any drop out. I would also record PCM voltages, ignition switch voltages (or power moding), RPM, O2 sensors, MAF, MAP. If it's available, I would also add the SAIS valve status.

With issues like this, you're flying blind without the ability to monitor and record data.

So yes I still have the EV fan. The secondary air injection system is whacked. I get the jet engine sound on startup. It runs for about 10 seconds and then it winds down. So I'm guessing it's related to that. You had told me a long time ago that this can be disabled with a tune, but I don't know if that will also solve the problem in this post or not.

So the electrical Gremlins problem is a real problem for me. The gauges don't go dead, but I have had other problems that I can't figure out that seem to be related to rust.

I had a problem with the braking system that eventually was sorted out when I went through and started checking and cleaning grounds.

Right now I am having an on going problem with my vent valve. I've tried to fix it but without much success. That's causing me not to be able to get the car inspected.

I feel like this vehicle is nearing the end of its viable service life. I don't have the time to try to fix this. Not because I am lazy, but because I don't have the knowledge to try to iron out all of these problems without spending an inordinate amount of time to go through each one. I don't have a good place to work on it. There's a place that rents bays but a problem like this could take me days or weeks to troubleshoot so its not worth it at $35 per hour to rent a bay. I only have about 6 inches on both sides when it's in my garage. I'm not whining. I'm very thankful I have a garage at all, but it really does make it difficult to work underneath. Swapping my transmission in my garage was a nightmare.
Unfortunately I do not have the money to buy a new vehicle, but what else is new.

So after reading your post and the other one, (Thank You both very much BTW), if I went outside and worked on it right now, I wouldn't even know where to start.

One would think the vent valve problem (p0449) wouldn't be a huge deal, but I've checked the basics. I also get an O2 sensor heater circuit code (p0135). I've replaced both cause I had an inefficient cat code, but that went away. Uggg...it's a flipping mess man. It's overwhelming. I feel like if I could fix what's causing the two codes I have, say if its a ground problem, it might sort out some of the other things. Anyway, thank You for trying to help this hopeless person.

 

[Mooseman]

We all know what it's like trying to keep an old vehicle going. Don't give up hope.

Sounds like the SAIS is actually working correctly. When I had mine, that's how it worked. I deleted it preemptively.

I would still try just unplugging the EV fan. If it clears, that's your culprit.

 

[mrrsm]

...and in an interesting "hybrid" discovery of this issue, "Crazy Ivan" The Man From PHAD (Pine Hollow Auto Diagnostics) gets schooled by Keith DeFazio from New Level Auto Repair during his visit to Keith's Shop up in Staten Island, NY during a brisk Winter Storm....and tackling this unique GMT360 Case Study.

The Key Tool (besides Keith's similar insight into what @Mooseman has recognized and pointed out above) involved hooking up an Oscilloscope to the Suspect Trailblazer and catching this Electro-Viscous Fan problem "In The Act" of Very Sketchy Behavior after Keith observed what was happening:

The Money Shot? The Speed Sensor inside of the EV Cooling Fan causes the 5 Volt Reference Signal inside the PCM to get "Wonky" and the APP and Throttle Body SHARE that same 5 Volt Reference Signal. Anything that threatens the PCM with "Losing Control" over Acceleration...will induce a "Reduced Engine Power" Response.

This can NOT be observed without the use of an Oscilloscope... noting that Ivan first Back-Probed the PCM for the TPS1 and the APP for Throttle Position Controls to observe those Signal Drop-Outs and *Glitches* and eventually, he focused ENTIRELY upon hooking up the Four Channel PICO-Scope to the EV-Fan Harness Connector to specifically Back Probe the "EV Fan Internal Speed Sensor":



...as well as the PCM "TPS1 Sensor Signal" Back Probe and BOTH 5 Volt Reference Signal Wires to nail down the Cause and Origin of this problem: