Electronic Throttle Control

CapitalTruck · August 3, 2009

There are times after I have been driving for a while that my truck truly accelerates on its own (I let off the pedal, it slows down some, but it definitely is still applying some gas) It can do like 35 mph. When I took off the air intake (engine off), the throttle plate isn't completely in the vertical position. Is that plate supposed to be completely 90 degrees when the engine is off? Basically, is there enough room in the throttle body for the plate to be completely vertical? Has anybody else had this problem? I was thinking of having my PCM reflashed. It happens especially frequently if I have been using cruise control for a long time.

brims · August 3, 2009

With the engine idling you need the butteryfly valve open slightly to get some air, so they probably just set that as the neutral position for the butterfly valve so they don't have to keep it open electronically to idle.

It seems the programming for these engines are to keep the throttle cracked to help with gas mileage instead of getting engine braking.

mr_bots · August 4, 2009

Default is not completely closed. Did a little test...unplugged the electrical connection on the throttle body and it started. Had a MIL light and said "reduced engine power." Just did it out of curiosity. Might just be a bad ECU or TPS. Might want to re-seat the connectors on the throttle body, gas pedal, ECU, and unhook the battery for ten minutes to reset everything.

CapitalTruck · August 4, 2009

Man, thanks for that good advice. I appreciate you having done that. I'll try a reset. You know, I don't think that Electronically Controlled Throttles would have throttle position sensors. It already knows where it is right since it's controlled electronically?

Spurshot · August 4, 2009

My 99 has a direct throttle cable to pedal connection. It completely closes the butterfly on the throttle body. The completely closed position is not 90 degrees. It's about a 80 degree position but you cannot see light around the edges of the butterfly. I just worked on this the other day.

You may have a bad/dirty "gulp" valve. This valve lets air in the inlet when you let off the pedal (close the throttle) thru a bypass, thus preventing a rich condition when you let off the throttle. It's an anti-pollution device. How well these things work depends on the design and control of them. Since the early seventies these things have been used off and on in some form or another. They give a feel that you really didn't let off the throttle all the way, and the engine takes a few seconds (sometime longer) to come down from some intermediate power. The valve on the 99 throtte body is at the base of it and is controlled by an electrical connection. Two screw hold it on. The throttle body should be removed and cleaned along with this valve. It'll have a bunch of carbon like soft buildup in the valve passage as well. Cleaning it may help.

CapitalTruck · August 4, 2009

I think in 2004 they instituted a drive by wire system, this elimintated that gulp valve (the funny thing is I can still see a stamping in the metal of my throttle body where you describe that component as being previously located). I'm glad to hear the 80 degrees thing, that's about where mine is. I'm definitely going to clean the throttle body out. When I took my intake hose off there was some oil that had kind of "pooled" up right where the hose connects to the throttle body. What would have caused that. I took off the PCV hose and confirmed that it was clear.

Spurshot · August 4, 2009

My 99 had a hose in and a hose out. both were coolant, one from the block, the other to the radiator. There is a third hose as well. It looked like the breather/pcv valve.

With a computer controlled electronic injected motor with fly by wire, the gulp valve function could just as well be done with the throttle position staying open a bit and the fuel injectors shutting down. Or they could move the valve to the manifold like some of the old engines.