I finally got my car back on the road after having it stolen and crashed into a house!
The car is driving like it was before, however I have a strange issue I cannot resolve. The car is idling high. The TPS is at 18.8%, even after I reset it with a PDU. I reset the idle adaptations as well. I replaced the TPS with a brand new one about a year ago, finally solving my trim issues. I did try to force the throttle butterfly back by hand (from the top of the spindle), but I didn’t get any movement on the TPS reading.
Here are two unusual clues:
While sitting in traffic, I shifted into neutral, the RPMs went up to about 3,200 and steadied. I then shifted back into drive and the RPMs went back to 900 but the TPS went down to about 14% then casually floated back up to 18-20%.
When I start the car cold, after about a minute, the car seems to want to lower it’s idle RPM, but then goes up. Every 10-15 seconds or so, it tries to drop the idle, but then races back up to about 1,500. Admittedly, I wasn’t watching the TPS through my OBD2 reader. Once I drive and the car gets hot, and it is what I reported above with no obvious attempts to lower idle.
Unplugging IACV had no effect. Unplugging MAF killed the engine.
We’ll never know, I am afraid. According to VK, the AJ16 ECU does not clear adaptations and retains the trim memory even with the battery disconnected, hard to imagine that unplugging the connector did something to reset the values…
I have not tried to set adaptations on a 4.0 XJS in a long time but I know the XJ6 (X300) can be set with both WDS and IDS. XJS was kinda strange with WDS/IDS communications.
There were issues and some ‘work-arounds’ that we used at the dealer but that was 20 years ago. I forget more than I remember about these old cars.
I own both PDU and WDS. When I attempt to reset adaptations using the WDS, it asks me for NOx emissions amounts… PDU does it without asking for any more info.
I’ve reset the TPS numerous times with a PDU. (I’ve also reset throttle adaptations, oxygen sensors reorientation and the throttle kickdown test) It starts off good, but then as I drive it, it seems to want to return to the 18.8-20% range!
I noticed that the ram intake assembly came apart. I owe it one large hose clamp to keep the plastic parts from pulling apart again. I don’t think that’s what’s causing it though.
While the car is running, I cannot seem to affect the idle by pushing on the throttle assembly, or the TPS. I can get the engine to rev using the throttle, but I can’t get it to slow down from its high idle, obviously caused by the higher TPS.
Is there anything that affects the TPS? Anything that can tell it to open up? No, right? It would have to be a bad TPS? Would unmetered air cause something like this? What about anything on the exhaust side? LTFT is 0. I would think that anything going on with unmetered air, etc, would cause fueling issues without causing the TPS to report anything different?
I’ll pull the throttle body off this weekend and take a look. I thought the TPS was simply reporting back what position the throttle plate is at based on my foot. There should be no way for the TPS to affect the position it’s reporting to the ECU, right?
If the TPS is reporting it’s at 18.8%, then it’s either busted, or the butterfly is getting stuck? There’s nothing else that can affect what the TPS is reporting back to the ECU, via OBD2, right?
To idle at 3000+ rpm, the engine must be getting sufficient air somewhere. Seems to me the TPS is possibly telling the truth, ie, butterfly not closing?
I think it must be…I didn’t have time to start the engine, but I did take off the intake elbow and I’ve attached what it looked like inside…pretty clean. I did spray some carb cleaner in there, so that’s the before picture. I didn’t take an after picture.
I may have to take the darned thing off this weekend and have a look around if the quick clean i gave it didn’t fix it.
There a wee bit of slack in the throttle cable, so I don’t think that’s the issue, but I will disconnect it and see where the car sees the TB butterfly at that point. That’s a good test for that.
It will occasionally show me that it’s down to 13.1%, it then creeps up to 18-20%. There isn’t anything the engine or the intake can do to force that butterfly to open, right? That would be crazy.
So cleaning helped. I’m back to 13.8% at idle. If you zoom into the butterfly open picture, you’ll notice a slight ridge that seems to form half way up and continues on the upper side of the throttle intake. Goes to show you, always clean that throttle body when you have issues with idle.
The engine speed has not followed suit, unfortunately. The car idles at 1,500rpm. When I shift into neutral while coasting on the highway, the tachometer races up to 3,000rpm when shifting into neutral. Once the car slows to a stop, it does drop down to 1,500.
I did a manual reset test of the IACV and I was able to get the car to idle normally. I may have to do another TPS reset. If that doesn’t work, I should look into the IACV. No matter what, it seems the throttle body is coming off!
I installed an oil catch can that, as you can see, has done a marvelous job at keeping the throttle body clean…to the naked eye. This issue that arose, I fear defeats the purpose of the oil catch can. I thought I may have found a way to keep the throttle body maintenance free…alas, there is no way around a good old fashioned throttle body cleaning.
Luckily it’s easy to get to, remove and replace. No gaskets, not much of anything. Once the throttle body is off, the costly TPS can be easily removed so that there is no fear of damaging it with carb cleaner. At that point, you can go to town with a bottle of cleaner and a rag or two.
Problem has been resolved. It was a almost imperceptible ridge of dried oil, likely from the intake elbow. Sitting for a few months allowed a slight ridge to form preventing the butterfly from staying closed. A quick clean eliminated this ridge, and a TPS reset was then able to get me back to normal.
