High idle after WOT
04-03-2020, 07:15 PM
#1
High idle after WOT So after a 411 to p59 swap I have a high idle after a WOT pull . But if I drive it normal it runs perfict in every way . The TPS voltage at idle is .35V but after a WOT pull it will hang and the tps voltage is .51v. Could this be a bad TPS switch . **** driving me nuts .
04-03-2020, 08:41 PM
#2
TECH Resident
Sounds like the throttle plate is sticking after opening all the way. It could also be a sticky cable if you're running dbc. You might find it's just a tps not being able to cover the entire range. I'd lean towards the cable or throttle plate sticking.
04-04-2020, 09:02 AM
#3
But with the car off and hooked up to HP tuners , I can sit in the car can hit the gas and watch the voltage on the tps . I works just fine . It dosent stick. U would think if it was the cable or the tps or any thing else u would see it then . But when u drive it it will stick after a wot pull . But never sticks when u drive like a normal person . I am not normal .lol
04-04-2020, 04:16 PM
#4
TECH Resident
When driving the engine is hot and vibrating. If you have the throttle body coolant line still hooked up that could be causing just enough expansion to cause a problem. The vibration could be just enough to make the cable end stick a little.
You can check the plate just by warming up the car, taking off the intake duct so you can see the throttle plate, then turning the throttle lever by hand and seeing if the plate moves smoothly and returns to closed when you let go. It may not be fully returning once everything is warm. In the old carb days that was a symptom of a worn out throttle return spring.
For the cable you can just watch to see if it moves from the bracket or if it binds up when doing the throttle plate test. You're looking for a kink in the steel wire or the plastic end piece lifting from the bracket on the throttle body.
It could also be an injector that sticks open or the fuel pressure not dropping enough after wot and forcing the injectors open a little. Not likely, but it's a possibility.
If the tps voltage is right through the entire range when the engine is hot then you can rule that out. Just remember that testing while cold won't tell the whole story since electronics tend to act up when exposed to heat.
You can check the plate just by warming up the car, taking off the intake duct so you can see the throttle plate, then turning the throttle lever by hand and seeing if the plate moves smoothly and returns to closed when you let go. It may not be fully returning once everything is warm. In the old carb days that was a symptom of a worn out throttle return spring.
For the cable you can just watch to see if it moves from the bracket or if it binds up when doing the throttle plate test. You're looking for a kink in the steel wire or the plastic end piece lifting from the bracket on the throttle body.
It could also be an injector that sticks open or the fuel pressure not dropping enough after wot and forcing the injectors open a little. Not likely, but it's a possibility.
If the tps voltage is right through the entire range when the engine is hot then you can rule that out. Just remember that testing while cold won't tell the whole story since electronics tend to act up when exposed to heat.
04-06-2020, 02:20 PM
#5
TECH Fanatic
I’m guessing you have to “goose it” to get it to settle down? If it’s behaving like blade is still open, it might still be open a bit. Could be gummed up as stated already, which is the first thing I’d check. Check the cable too, and make sure the tensioner on the cable is tight and it isn’t slipping. There’s a disconnect in the middle the needs to be tight. If it’s not, this can easily happen.
If you have the 3 cable setup (cruise control and traction control/ABS box) check it too for issues. I had a bad cable once upon a time that would not allow WOT because it was loose at the disconnect in the center. I ran it with a chunk of rubber around it and a few small hose clamps for a while to hold it in place. Worked fine lol. I replaced it since. It’s just a plastic connector/adjuster that snaps together on the cable. If I was near my car I’d snap a pic and post it. Can’t miss it though. Just make sure you’re getting full range. I’ve had to build my own brackets and relocate these things multiple times, it is not a difficult setup.
If you have the 3 cable setup (cruise control and traction control/ABS box) check it too for issues. I had a bad cable once upon a time that would not allow WOT because it was loose at the disconnect in the center. I ran it with a chunk of rubber around it and a few small hose clamps for a while to hold it in place. Worked fine lol. I replaced it since. It’s just a plastic connector/adjuster that snaps together on the cable. If I was near my car I’d snap a pic and post it. Can’t miss it though. Just make sure you’re getting full range. I’ve had to build my own brackets and relocate these things multiple times, it is not a difficult setup.