Truck tries to drive through the brakes

[Erik the Awful]

Every time I've had an engine pull without input, there were throttle plates opening.

'76 Cadillac - Accelerator pump linkage broke and got hung up, holding throttle open.
'69 Cadillac - Secondary return linkage was missing, vacuum pulled the secondaries open.
'06 Mustang - Carbon buildup in the throttle body stuck the throttle body slightly open.
'89 C1500 - Holley sniper throttle plates were misaligned from the factory, sticking slightly open.

Recheck your throttle plates. Play with them and play with them some more.

 

[Caman96]

Every time I've had an engine pull without input, there were throttle plates opening.

'76 Cadillac - Accelerator pump linkage broke and got hung up, holding throttle open.
'69 Cadillac - Secondary return linkage was missing, vacuum pulled the secondaries open.
'06 Mustang - Carbon buildup in the throttle body stuck the throttle body slightly open.
'89 C1500 - Holley sniper throttle plates were misaligned from the factory, sticking slightly open.

Recheck your throttle plates. Play with them and play with them some more.

^^^Thats what I’m sayin’. Never hurts to clean your throttle body either.

 

[PJones96]

^^^Thats what I’m sayin’. Never hurts to clean your throttle body either.

I will clean the throttle body. The idle issue is just little blips every 3 seconds. The truck doesn't rev on it's own until I put it in drive. Seems like if it was the throttle blades it would be constant, right?

 

[Pinger]

The truck doesn't rev on it's own until I put it in drive.

Throttle cable being disturbed by transmission selector/cable?

 

[Caman96]

I will clean the throttle body. The idle issue is just little blips every 3 seconds. The truck doesn't rev on it's own until I put it in drive. Seems like if it was the throttle blades it would be constant, right?

What does scanner say throttle position is?

 

[tayto]

i have seen throttle shaft that are worn and wont let the throttle blades close completely

 

[PJones96]

What does scanner say throttle position is?

Scanner says TP is .4 to .8 while idling in park. I put it in drive, the TP% remained the same but rpm increased. I did not notice how high the rpm got but after holding it for a few seconds the idle did come down to 607.

With the engine off the MAP is 29.8. When idling the MAP read 8.6-9.2. When I put in in drive the MAP increased to 10.9.

Intake air temp was a balmy 111.

Spark Advance ranged from -18 to -22 while idling.

 

[Caman96]

My TP is 0° at idle and while driving with foot off pedal it also returns to 0°.
Watch it while driving and what do you see.

“

1. Failing throttle body​

A car accelerating on its own without the driver’s input is commonly caused by a malfunctioning throttle body. If the throttle plate of your car sticks, it cannot return to the correct position, so the car will accelerate as a result.

 

[PJones96]

My TP is 0° at idle and while driving with foot off pedal it also returns to 0°.
Watch it while driving and what do you see.

“

1. Failing throttle body​

A car accelerating on its own without the driver’s input is commonly caused by a malfunctioning throttle body. If the throttle plate of your car sticks, it cannot return to the correct position, so the car will accelerate as a result.

Understood. I need to clean the TB and make sure the throttle blades close completely. TPS should read 0

 

[TuckerDog]

Try checking vacuum level, air fuel mixture, throttle linkage, timing, make sure the ignition is functioning ok. And then after all that, go ahead and check the brakes.