Faulty TPS? (no CEL or codes)

[shadow460]

I just wanna confirm before I spend $20 on a part. My 98 Expedition's 4.6 liter engine will attempt to surge at idle and will race sometimes when it's put in Park. My scan tool, the Actron CP 9180, shows the "Absolute TPS" reading at 18.4 % when the engine is idling normally, and shows anywhere from 20.4% to 24.1% when it's trying to race or lunge. It will usually stop acting up if I blip the throttle a time or two while going down the road.
I just pulled into the driveway with it idling normally and pushed the throttle until the scan tool said 20.4%. The engine speed went to around 1,700 RPM. I pushed it to 24% for a few seconds and the engine speed was almost 4,000 RPM.
Something else I noticed is that if I barely hit the throttle, it'll read 40% open.
I had considered a possibility of a vacuum leak, but the fuel trim levels are around 33%.
I think the TPS is either loose or sticking. I don't feel any roughness in the throttle pedal itself otherwise I'd suspect a sticking cable, plus it'll increase RPM on its own sometimes instead of just slowing to a given RPM.

 

[Thermo]

Shadow, it sounds like you need to clean your throttlebody. If the butterfly valve sticks even a little bit, it can cause what you are seeing. Then you can replace the TPS unit. I had to replace the one on my truck (got some metal shavings inside of the sensor, guess I should have pulled that off before porting/polishing the intake, ooopps). Each change to make.

 

[shadow460]

How hard is it to clean the throttle body? Do I need to remove it from the engine, or just clean around where the butterfly valve "seals" shut?
I did have the air intake off the truck before I noticed this problem. I took the intake off to access the alternator when that went bad. Something might have gotten in there while it was off.

 

[Thermo]

Shadow, go to the auto parts store and get yourself some throttle body cleaner (NOT!!!!! carb cleaner). Remove the intake and using your finger, manually open the butterfly valve. If you see brown, squirt it with the throttle body cleaner. Pay special attention to the edge of the butterfly valve. Also make sure to get around the shaft that runs between the throttle linkage, butterfly valve, and the TPS. Let it dry and then give the shaft a little squirt of a light machine oil (less is more in this case). Start the truck up. You may have a little bit of a hard time starting it up as you have essentially flooded the truck. But, it will start. Once you get it started up, see what you have.

As for getting something inside the intake and holding the butterfly valve open, removing the intake will show you that. Essentially, if anything made it into the intake, the first time you gave the gas a significant push, you should have blown that item into the manifold itself. So, unless you have the inside of your intake coming apart, that is not very likely or you put something inside the intake to try and make it flow better.

 

[shadow460]

I took a clean shop rag to it before I read your last reply. Even just doing that has eliminated the racing and lunging problem. The throttle position snaps back to 18% almost all the time now when I release the gas pedal. A couple of times it went to 18.4%, so I think I need to clean it out a little more. I also need to clean out the air filter. It's got a K&N warning sticker on the housing, so I assume there's a K&N filter in there that hasn't been cleaned since the Cretaceous Age.