Continued Acceleration

[abgarza195]

I looked in the forum for a similar problem to the one I have but have not found one so I am posting it.

I have a 2005 GMC Sierra Crew Cab Z71 and just noticed this problem on Saturday 9/18

Sorry for the long post.

 

When accelerating from a complete stop and going over 1300 RPM I will let go of the gas pedel and the truck will continue to accelerate slowly and continue to shift from 1 - 2 gear around 1800 RPM and keep on accelerating. I will refer to this as continued acceleration as CA mode for the rest of the article.

If I do the same but keep the RPM below 1200 when releasing the gas pedal then the truck will coast along and the RPMs will drop back down to normal.

My RPM at idle is about 600.

 

When I am in this CA mode I can shift into neutral and the RPM will surge briefly and then quickly go down to idle at 600 RPM and remain steady.

If I press the brakes down gently the truck will slow down but you can feel the truck keeps pulling forward. From here there are two outcomes

1 - If I continue to hold the brake and slow the truck down enough then the RPMs will go back down to normal and the truck will not accelerate again once I remove the brakes. Thus overcoming the CA mode.

2 - Once I let go of the brakes the truck will continue to accelerate again. It's as if the truck remains in the CA mode if I only brake for a few seconds.

 

The truck had a slight idle issue, nothing major but I decided to clean the throttle body Saturday morning with SeaFoam Deep Creep. I only sprayed the throttle body and cleaned it with the blue shop towels. I did not spray into the air maniford nor did the induction cleaning method, just a simple throttle body cleaning to clean the butterfly valve front, back and around. The good news is the idle is great now but now this CA has occured after the cleaning and I don't know if it related or not.

 

Is it possible I damaged the throttle body electronics during the cleaning?

I only spraying inside the throttle body and non on the plastic case covering the electronics.

Any feedback would be greatly appriciated.

 

Extra info.

The truck runs great and accelerates without hessitation. It idles well and the coolant temperature gauge reading is normal. The RPMs seem to want to end up around 1800 - 2000 when going into this CA mode. The truck doesn't stall and there is no check engine light set and the truck has 108k miles. I have changed the spark plugs with the AC Delco Iridiums and have only used syntheic oil since the 5k break in period. I am the only driver and bought the truck new. I do not have a scan tool.

 

For tomorrow.

1 - I just remembered I had the cruise control switch to on, not set but only on. I will turn off the cruise control switch and see if the CA mode goes away. I always have the switch set to on.

2 - Clean the MAF with CRC MAF cleaner.

[abgarza195]

The good news is I resolved my unintended continued acceleration by cleaning out the MAF sensor with the CRC MAF sensor cleaner.

The resistors on the MAF looked ok but the connecting wires on them had small particles that you had to really look close to seem them.

One of the resistor wires had a large black particle about 0.2 mm - 0.3 mm on it that I could see while holding the MAF about a foot away from my eyes.

Kind of easy to see since the black spot was covering the resistor wire and it almost looked like the wire was broken.

The spray helped to clean the MAF but I still had to use the blue shop towels and roll the corners to use as a scrapper tool and knock the small particles off the resistor wires.

 

I failed to mention the only air filter the truck has ever used is a K&N air filter since the day I bought the truck. I've cleaned the filter twice and I take the extra time to oil the filter with the minimum amount of oil to make it change color. I know there is alot of forums indicating the oiled filters can lead to contaminates on the MAF. But for these contaminates to cause unintended acceleration was something new to me. Perhaps the big black particle I mentioned was K&N oil with some dirt? Who knows but if it was then it took 5.5 years and >108k miles of using this filter to have it contaminate the MAF sensor and cause this issue.

 

The bad news is my haste I did not record this unintended acceleration to prove the truck would continue to accelerate on its own. I was worried that the MAF cleaning would not help but it did. I figured it would cause the check engine light to come on if the TPS was in idle range and the MAF sensor was not in the idle frequency output range. I guess maybe the software is setup differently or my MAF output was still withing the acceptable range so the ECM did not set a DTC error.

 

I am glad this unintended acceleration has been resolved over the weekend because I was going to go straight to the dealer on Monday morning otherwise. I was worried that maybe the truck would go haywire on me and go into WOT acceleration but this was not the case.

 

Thx for your time.

[jro909]

i was going to say, if i'm coasting off a highway my truck will continue to maintaine speed and shift but i figured it was normal...

[abgarza195]

Yesturday when going 55 mph (about 1500 RPM in OD) I would release the gas and the truck would coast and slowly reduce speed like normal. Then when the RPMs dropped to about 1200 RPM you could feel the truck accelerate back up and pick up speed and the tack and speedo increased also. Afterwards (8+ second later) you could feel the truck stop accelerating and start to coast again and drop speed. The truck would continue to repeat the surge and drop of acceleration.

I took my wife along to confirm she felt the acceleration and she was freaked out.

Told me to get rid of the truck.

She was ready to get off the truck once she saw the truck shift from 1 - 2 and continue to accelerate on its own with out me pressing the gas.

Once you get it over the 1300 RPM range on 1st gear and let go of the gas the truck would continue to gain speed over 30 mph on its own. Sounds strange but I'm glad it's fixed now.