2002 Q45 Throttle body/throttle position sensor problem

Have a 2002 Q45 with 208,000 miles. Problem started with ignition coils going bad. Would get random misfires and some pointed misfires with codes. Would also cause very poor acceleration when engine was warm and after sitting in parking lot for 10-20 mins. Replaced all ignition coils then got a tps code. If the car is cool from sitting longer than 45 mins or overnight, the acceleration was fine, but then once warm the acceleration was poor. Finally threw the SLIP and TCS OFF. So replaced the throttle body with a used one. Corrected the SLIP and TCS OFF, but still having a starting and acceleration problem when engine warm and I’ve left the car sitting 10-20 mins. What is peculiar is I can pour water over the throttle body to cool it and it starts right up and runs normally until my next stop. Is it possible that my used throttle body is bad too. The only other code I have is P0720 and P1720 which is a transmission output speed sensor. I don’t think that should have anything to do with how the vehicle starts, idles or whether it will run or not.
Has anyone had experience with this same symptom? Your input would be greatly appreciated!

Thanks
Michael

to NICO! I haven't heard of them failing that way, but hopefully we'll get more input.

It might be possible that another sensor near the tps is causing the problem and is being cooled when I pour water over the throttle body. Still I’m wondering if the throttle body coolant flange or the coolant tubes going to or from it might be clogged, so I will check that next. I just keep seeing in forums how unrelated sensors are causing codes which have nothing to do with that particular sensor and don’t even throw a code for the failed sensor. For instance, what does SLIP and TCS OFF have to do with a bad TPS?

[email protected] wrote: ↑

Thu Dec 26, 2019 3:17 pm

For instance, what does SLIP and TCS OFF have to do with a bad TPS?

TCS modulates the throttle body to cut power to the wheels during an event, so if the throttle body isn't functioning properly, it goes offline. If you don't have a copy of the factory service manual, it's available at www.infinitiservicemanual.com. On my G35 there was a relearn procedure. I assume the Q had that too?

The one bit of advice I've heard and followed on these drive-by-wire throttle bodies is to not manually open the throttle plate to clean them.

Thank you Q451990 for your reply. Yes I already performed the relearn multiple times. I have discovered since my post that I have a TPS connector issue. Sometimes when the car heats up, the connector loses contact. I discovered this by disconnecting and reconnecting the the plug connector which resolved my problem for a while but it will come back frequently. I am now seeking a connector conductive grease or spray that I can put on the terminals to improve conductivity. Any suggestions?

Thanks again!

Btw- I already cleaned the terminals with electrical parts cleaner, but still have conductivity issues.

For electrical contact enhancement I like Stabilant 22. Here's a link to the product for convenience, I have no association or endorsement of this seller....
https://www.ebay.com/i/381762729543
Needs to be mixed with reagent grade alcohol (not the drugstore 91%IPA).
But, you might first check that you have good mechanical contact (pin/socket not recessed, crimp at socket terminal good. The intermittent could be in the backshell of the connector......

Yep. I'd check the connector's mechanical connections first. Sometimes you can tighten them by bending the male spades a bit, or putting a pick or small screwdriver beside the female connectors to close them slightly. I've used Stabilant before, but these connections should be ok if they're physically making contact and there's no corrosion.

Purchased remanufactured throttle body. Still getting VCS OFF and SLIP lights. On prior used throttle body, I would get these lights but if I unplugged and plugged back in, it would work for short duration, the the lights would come back any the unit would fail. Thought I had a bad unit, so bought a reman unit. Now thinking I may have a failure in the harness or terminals/connector. Looking at the pin test for confirmation. Anyone with experience doing the pin tests?

New throttle body and did relearn procedure. Ok now car runs fine until warms up, then will not start or idle. Cools down runs fine until warms up, then same issue. No codes other than 0720. Bought the speed sensor, but haven’t installed yet. Has nothing to do with start or idle. Is there another sensor that is temperature sensitive that could be failing but not giving a code? Cam position sensors or crank position sensor? Completely lost now...no codes related to stall, misfire, maf, and has all new plugs and ign could

Researching same problem on others’ Nissan and Infiniti vehicles and consensus seams to be bad camshaft position sensor(s). How could you have a bad sensor but no code for that sensor? Must have had theottlebody and sensor(s) fail at same time. Throttlebody corrected the SLIP and VDC OFF lights but still stalling, failing to start once warmed up. Cools down - everything works again. Heats up - fails again. I’ve read that cam sensors can fail with heat due to weak or broken spring contact. Does this sound accurate based on the design and function of a cam sensor?

I think someone with more experience with your engine will be by later today with some thoughts on this.

Thank you- that will be greatly appreciated! This problem has me worn out, and with no codes makes it even more frustrating.

Howdy. I'll take a stab at it.

1. Relearns
You mentioned that you have already done the relearn. I'd like to verify that that includes all 3 relearns - Accelerator Pedal Released Position, Throttle Valve Closed Position, & lastly Idle Air Volume Learning.

2. Fluid levels
How is your brake fluid level? While looking around, I'd check the ABS connector area.
How is your coolant level? Check the condition of the tubes supplying coolant to the throttle body spacer. Make sure that the tubes have coolant and it flows (so yeah, spillage possible)

3. The Achilles heel of sensors.
Honestly, diagnosis of most mysterious VK45DE engines starts with the camshaft sensors. It doesn't always throw a code, but will usually cause starting and driveability issues.
I don't see the classic symptoms in your description, but what I usually recommend is this - if your vehicle has more than 130k miles and/or you do not know if that sensor has been replaced, then just replace it. It's not a matter of "if", but rather "when" it will fail.
My recommendation is to buy an OEM sensor and replace the camshaft sensor. (Don't throw the old one away yet).
If nothing improves in the vehicle behavior, then we can assume the camshaft sensor was not the issue. At that point, you can keep either the new one or old one at the camshaft sensor location, and swap the free sensor with the one at the bottom of the engine - crankshaft sensor.

If nothing improves, no harm, no foul. We have eliminates the troublesome sensors as the cause of the behavior. Just hold onto that spare sensor, because remember, it will certainly fail.

4. Intake
Have you checked you intake tubes for cracks and such? What is the condition of your air filter & mass airflow (MAF) sensor?
Do you still have the OEM air intake setup?

5. Connector
Did the suspected connector issue get resolved by replacing the throttle body?

Yes did all 3 relearned and to be honest I don’t understand the purpose of #2 in the relearn procedures since it is virtually identical to #1 except you only do it once.

All fluid levels are good. Throttle body connector issue is resolved.

The most unusual thing is when it fails I can literally trickle water (about a gallon) on the driver side bank to cool it off and wahlah it will start and run fine again. I read that the coolant temp sensor could be suspect and considering that it is on the back of engine on the driver side bank, I thought I might be cooling it and helping it operate again. What doesn’t make sense regarding that is the temp gauge on the dash doesn’t fail and the heater fan when auto is selected will come on when the engine temp reaches desired temp to operate the fan. Does coolant temp sensor control that function or is that controlled in the heater unit or core itself? I also thought the cam sensor might be cooling down from water as well. Checked the MAF plug and get 0V, 1V, 4.7V, 12+V, and 5V on each pin IF I remembered the order correctly.
Just changed the cam sensor on the driver side and have not yet experienced the problem but temp is cold and I will know more with longer drive tomorrow. I repaired the intake tube awhile ago with silicone tape because of stalling on take-off. That worked beautifully for $10 rather than $300+ for new one. Anyway almost positive no issues there because it runs very well when cold. Thank you for sharing your knowledge and experience with me. Sometimes sucks when you can’t find exact symptoms and vehicle online, but every piece of knowledge helps form a better diagnosis.

One other thing. Someone mention knock sensors but I don’t have knocking unless car has sat for days without being driven and very cold. I thought this might be due to oil settling too much / does this engine have push rods or hydraulic valve actuators? Never a problem otherwise...

Your engine has overhead cams with bucket lifters that are shimmed if I remember correctly. The cold startup noise you hear is probably timing chain tensioners building pressure. Knock sensors are just microphones to listen for spark knock (the rattle you might hear going up a hill on a hot day). The ECU uses this information to change timing maps to try to eliminate it. You would see codes for them if there was a failure.

How are you scanning for ECU codes? If you don't have a Bluetooth scan tool that works with a smartphone or tablet, that could be the best $5 you ever spend on eBay. It would show you the temperature reading from the temperature sensor in real time on your phone or tablet.

Ok what else can cause VDC OFF and SLIP and CEL? I replaced Throttle body with reman unit. Getting lights again. Already verified connector and wires good. Is there any other sensor that can trigger these lights?

What's the code for the CEL? Slip/VDC off can come on for almost any reason the car isn't happy, including camshaft/crankshaft sensors.

Current codes
P0720 have new sensor but haven’t installed yet
P0120 installed new throttle body
P1121
P0300
P0171

Mass AirFlow sensor. It is also the air temperature sensor.
Do you by chance hit any RPM limit during these episodes?

I don't think I got the full picture regarding the rest of yoir intake. Was the silicone repair made before or after the MAF sensor housing? How is it holding up at present?
Is everything upstream of the throttle body otherwise stock?

Try testing the MAF by disconnecting it while the car is running (after getting to temperature, as you described above). The engine should cut off.

The intake hose is fully closed in with silicone tape. The throttle body was replaced with Card One reman unit. Don’t get rpm limits during episodes but when the VDC OFF and SLIP lights are on it will not start. When the lights first started it was the throttle body. Replaced and would not get the lights. Now the lights are back. Have not replaced MAF sensor. Have replaced the camshaft position sensors, but not crankshaft sensor.

When car is cold everything works fine, except shifting of course due to speed sensor p0720. But engine is fine when cold, but gives trouble when warm...nothing makes sense. Wasn’t getting any codes other than P0720 speed sensor until today. The new throttle body has been on for 2weeks now and still have issues when engine is warm.

MAF is stock Air duct is stick with silicone tape to seal cracks - no leaks on unit. Don’t believe MAF has ever been replaced, but has been cleaned. Last start could not exceed about 2000rpm. Now that engine is warm again, will not start.

If I were in your position, I'd wait for the car to warm up then do the simple MAF test described above.

I can't vouch for the integrity of a full silicone repair. Maybe pictures will help.

I suppose I should say, keep car running until warm. Then disconnect MAF

Done that before and car died. But haven’t done it in a while. I will purchase one online. Not willing to pay $300-400 from autozone or Nissan. Did see one at autozone for $149 - Duralast not Hitachi

Have seen them as inexpensive as $30+ on ebay

Rock Auto can be a good source for Hitachi parts. It'll usually tell you if it's the OEM parts for your car as well.

Ok so I’m almost 100% certain that I got a bad reman unit (throttle body) from cardone. Worked for about one week then same codes and issues as the last used throttlebody. With this reman unit, if I trickle water over the throttlebody and TPS on back of throttle body to cool it down, it works fine then drive it a few mins back to operating temp and throws the SLIP and VDC OFF lights on again. Stop pour water on TPS, starts again no lights and runs fine until it heats up again. Problem and solution can be duplicated over and over again. Planning to send unit back for replacement as defective unit. Before I do I have a question - Does the coolant control valve control flow of coolant to the coolant ring between throttlebody and intake housing? If so, shouldn’t I see a code for that malfunction when I scan using pocket scanner?