Engine RPM won't decrease normally when off the throttle

[Bullet4x4]

This weekend I had my oil changed to Valvoline MaxLife 10W40 to help with my minor oil consumption that I had during startups. It has managed to do this quite well, however I noticed that my throttle response has suffered right after the change on my way home.​

When I press the throttle and let off, it takes approximately 10 seconds for the rpm's to slowly drop back down to idle/cruise while driving. It is worse in neutral when there isn't a load on the engine. I thought I would ask if anyone else has experienced this as this seems like to much for something to be caused by a slightly thicker oil. What else could have changed to cause this?​

Any help is greatly appreciated. It is annoying to drive like this as it has become much more of a chore to maintain proper speeds. I often have to resort to using the brake since the engine keeps going after I let off.​

 

[Thunder]

Sounds like you may have a vacuum leak. Maybe a vac line got knocked off or broken when the oil was changed.

 

[andyblack]

Is your engine fuel injected? I had that problem once and it was caused by a bad throttle position sensor (TPS), located on the trasmission. It was really annoying.

 

[BoondocK5]

Like Thunder said, I got a donut on it being a vacuum leak

 

[andyblack]

Yes, vacuum leaks will make it run like crap! You can find out if it's a vacuum leak by taking off the air filter housing and covering up the top of the carb or throttle body with your hand, and if it doesn't stall out but tries to keep running, you have a bad vacuum leak. Most of the vacuum lines on my engine are so old and brittle that it's a wonder they don't all leak like crazy. You may have to go through and see if they're all connected right, and if they are, disconnect each one until you find which one's making it run bad.

 

[Stomis]

Is your engine fuel injected? I had that problem once and it was caused by a bad throttle position sensor (TPS), located on the trasmission. It was really annoying.

Who told you that? I'm pretty sure the throttle position sensor is on the throttle body not the transmission.

 

[andyblack]

This was on a '91 Dodge truck with a throttle body injected H.O. 360 and an NP435 trans. There could be another one somewhere, I don't know. It was just this little meatal can with two wires sticking out of it that was on the driver's side of the trans. Replacing it fixed my problem. I can only speak from my own experience. Hopefully it will help someone. The throttle on that truck would get stuck for more than 10 seconds sometimes. It was pretty frustrating because you had to stomp the gas pedal a few times to make it stop and even then you sometimes had to just live with it. Since it had a manual trans, you could disengage the clutch or put it in neutral if it started acting up too bad. I'm glad I got rid of that truck.

 

[Blue85]

You didn't say what year the truck is. Something easy to check is that the throttle linkage isn't caught on something - make sure it's snapping back to the throttle stop each time it's moved. The cruise control linkages on the carb trucks had a way of binding up sometimes.

But look at all the lines and linkages near the oil fill.

 

[andyblack]

Okay, update. I was thinking last night about this. The sensor that I replaced on the side of the transmission was the VSS (vehicle speed sensor). I replaced it because the speedo wasn't working. I got mixed up because I replaced the TPS at the same time. (All those letters are confusing). I can't remember exactly where it was at. That was over ten years ago. Sorry for the misleading info.

Stomis, thanks for calling me on that one. That's what got me to thinking about it. Whenever someone posts something that's questionable, you don't hesitate to wave the BS flag. I also had a nightmare about you and the guys in your band. Yikes!

 

[Stomis]

Okay, update. I was thinking last night about this. The sensor that I replaced on the side of the transmission was the VSS (vehicle speed sensor). I replaced it because the speedo wasn't working. I got mixed up because I replaced the TPS at the same time. (All those letters are confusing). I can't remember exactly where it was at. That was over ten years ago. Sorry for the misleading info.

Stomis, thanks for calling me on that one. That's what got me to thinking about it. Whenever someone posts something that's questionable, you don't hesitate to wave the BS flag. I also had a nightmare about you and the guys in your band. Yikes!

Lol dude. That makes much more sense now!

Yeah I'm a straight forward guy. As you said if something dont sound right I'm not afraid to go against the grain and question it. Plenty of people have gotten kinda pissed at me on here now and again for it cause I come off as a dick sometimes but if it save someone from looking for the TPS on the trans than my job is done