Hello all!!! I’m facing an issue I can’t solve on my own. My throttle won’t shut at idle. The shutter stays slightly open between 2.7 and 3.2 %. Car shakes, graphics show it’s not stable at all. It bounces all the time. Does someone know how to fix this? It’s very annoying. It appeared after I solved a P1071/1074 vacuum leak. I’m thinking maybe the car learned wrong from that period? I tried to reset the TB by unplugging the IAC engine running after a hard reset but it’s all the same. TPS works fine I think. Response is good. Cable is not too tight nor too loose.... I’m lost. Thanks in advance for your help !!!!

 

Oh, I forgot to mention the car in question is a 2001 3.2 308

 

Or is that percentage of opening actually correct? That would mean something else is causing my rough idle. Note there’s a hissing sound coming from the TB. I’ll drive tonight to see if codes arises. So far I’ve only got the P1071/P1074

 

Have you tried to clean the throttle bore and plate? Is there just a bit of slack in the accelerator cable? Does the throttle plate close if you push on it with your finger?

Sounds like a vacuum leak in the air hose from the filter.

 

TB is so clean you could use it as a dish. It was thoroughly cleaned when the engine was rebuilt a few month ago. Throttle plate closes perfectly when I push it with my finger. So it’s not off place! Air hose is CHECKED. Perfect. No leak at all. The slack from the accelerator pedal is as minimal as can be.

 

I presume you mean you got codes P0171 & P0174. If they show again, look at other things (other than vacuum leak) that can cause them:

 

Car ran fine yesterday. Idle is a bit odd at startup (it seems too low) but when driven it’s alright. When I’m at a stop light however the idle sometimes drop like someone taking his breath. Instant drop and return to normal 6/700 ish. After one hour drive both codes came back. I inverted 1 and 0 typing earlier but you corrected me :-) I did have three leaks I cured so I assumed that was it. Obviously there’s something else. Injectors ans coils are new so (I hope) we can scratch that. Fuel filter is new too and full fuel line was air blown so it’s clean. Now: fuel pump and fuel pressure regulator are original from the car. I’ll look into it. O2 sensors are new. Wrong signal from TPS? I’m leaning towards that and I’m sainting to get a 5* T20 to take it out and clean it see if it helps.

 

But about the throttle plate position: we agree it should be closed right? Is there any procedure to rectify that manually?

 

The throttle cable should be adjusted to "neither tension nor slack" (workshop manual). I understand that you have adjusted it to this requirement.

The throttle plate is fully closed only when the ignition is "off". With the ignition "on", the throttle plate opens a bit as controlled by the TB motor (you hear humming from the TB). This initial throttle plate opening is electronically controlled so I don't think it is possible to adjust it (and I wouldn't mess with it).

 

Well, so I have a problem since my plate is slightly open ignition off... There should be a way to put it back in place somehow...

 

The throttle is controlled by the ECM. It is suppose to be open slightly 'engine-off' so the engine will start next start cycle.
The idle is controlled by the throttle plate and IACV in the throttle body.

The throttle motor is pretty strong so DON'T put your fingers anywhere in the bore with KEY-ON!!!

 

Just had a look at my new (spare) TB but it is for AJ26 engines and you have AJ27 which, I believe, has somewhat different TB. Anyhow, the throttle plate on my new TB sits practically fully closed but I can see a very small gap towards the bore, something like 0.5 mm. The identical TB currently running on my engine will open to something like 5-6 mm with the ignition "on".

I can also see on the new TB that there is an adjuster/stop screw for the "cold" (the 0.5 mm) position of the throttle plate. The screw is just below the bell crank (to which the cable attaches) and it is covered with white paint to preserve the factory setting. If you have more than the mentioned 0.5 mm gap between the throttle plate and the bore, the factory setting of the stop screw has either been altered or your throttle plate does not, for some reason, go all the way back to the screw-stop.

Does your TB look like this or is it different?

 

Hello! Thanks for chiming in :-) my TB doesn’t have that black kettle on top. I think yours is the earlier model... So there is a small gap? That’s interesting. Have anyone measured it using the OBD? Based on what I read so far it should be less than 2%. Mine is way more....

 

Our TBs are Japanese right? I’m wondering if I could find relevant infos on jap car brands for an electronic reset... Like this procedure on Late 90s Nissans for example:

ECU Accelerator Pedal Reset Procedure
Note Timing is critical for this to work!
1. Turn the ignition switch to on. Dash gauges lit. Don t start the engine!
2. Wait 3 seconds.
3. Fully depress and release the accelerator pedal 5 times within 5 second.
4. Wait 7 to 10 seconds.
5. Fully depress the accelerator pedal for approximately 10 seconds. At this point the check engine light starts blinking quickly indicating Diagnostic Test Mode II (Self-diagnostic results) has started.
6. Release accelerator pedal and wait 5 to 10 seconds.
7. Fully depress the accelerator pedal for 10 seconds. At this point the check engine light should change to blinking slowly indicating “Erasing ECU Memory”.
8. Release the accelerator pedal and turn the ignition switch to off.
9. Restart the engine. The check engine light should be out.
Note: If the check engine light doesn't blink as described in steps 5 & 7, then the ECU isn't reset.
* If above didn't work, disconnect the battery negative and pump the brake to discharge the ECU capacitors. This method is almost foolproof as long as all ECU control parameters are within their normal ranges.
Resetting The Throttle Body Calibration (this step is conditional)
A Rough Idle or a SES can sometimes be caused by a change in the throttle body position sensor calibration. To correct any accidental changes in throttle body calibration, use these procedures to recalibrate.
Note: These procedures are a little tricky to do. You must get the timing just right Use a stop watch to help the precision of your timing.
Accelerator Pedal Release Position Learning Procedure.
Make sure that the accelerator pedal is fully released. Turn ignition switch “ON” and wait at least 2 seconds. Turn ignition switch “OFF” wait at least 10 seconds. Turn ignition switch “ON” and wait at least 2 seconds. Turn ignition switch “OFF” wait at least 10 seconds.
Throttle Valve Closed Position Learning.
1. Make sure that accelerator pedal is fully released:
2. Turn ignition switch is “ON”.
3. Turn ignition switch is “OFF’ wait at least 10 seconds.
Make sure that the throttle valve moves during above 10 seconds by confirming the operating sound.
Idle Air Volume Learning (Throttle Position Learning)
It's best to time with a watch/clock.
1. Perform “Accelerator Pedal Released Position Learning”.
2. Perform “Throttle Valve Closed Position Learning”.
3. Start engine and warm it up to normal operating temperature.
4. Turn ignition switch “OFF” and wait at least 10 seconds.
5. Conform that accelerator pedal is fully released, turn ignition switch “ON” and wait 3 seconds.
6. Repeat the following (steps 7a, 7b) procedures quickly five times within 5 seconds.
7a. Fully depress the accelerator pedal (HARD)
7b. Fully release the accelerator pedal.
8. Wait 7 seconds, fully depress the accelerator pedal and keep it for approx. 20 seconds until the Check Engine Light (CEL) stops blinking and turned ON. .
9. Fully release the accelerator pedal within 3 seconds after the CEL is ON.
10. Start engine and let it idle.
11. Wait 20 seconds.
12. Rev up the engine two or three times and make sure the idle speed and ignition timing are within the speciations.

 

There should be some similar step by step procedure for our cats no? What do you think?

 

"Adjusting" it might be a good way to make things worse such as if you have an air leak, a dirty MAF, a weak fuel pump or any of a bunch of other issues.

 

Ok... I’ll check that fuel pressure first and clean the position sensor. I’ll see from there

 

MAF is new and no air leaks

 

Agree with JagV8.
From lots of reading in the FSM, I don't think the Jags have many procedures like that in the vein of some other manufacturers, of "secret menus" or procedures from pressing things in a certain order, like described above.

I haven't found an adjustment procedure for the TB, but I did find a detailed breakdown of the AJ27 TB, the one you most likely have. Page 56 here http://jagrepair.com/images/Training...ual-9-5-01.pdf tons of other useful info on that site as well.

I forget where I read about it but the AJ26 throttle bodies will typically sit "partially open" when the car's off, and momentarily actuate to fully closed, then back to partly open, when the car is turned on. Don't know if that applies to AJ27 cars since they're using electronic pedals, no throttle cable on those.

If you're trying to reset the learned engine trims, you can disconnect battery ground and touch it to battery pos to perform a "hard reset". Never thought to unplug the IAC while the engine is running, that seems like it would cause more problems...

EDIT: I just reread the thread, if you have a cable actuated throttle body (AJ26 engine) then all the things you're describing about TB performance (open at engine off, 2-3% TPS reading) are perfectly normal. Thought all cars after 2000MY were AJ27 engines. Scroll up a bit in that link for AJ26 TB info

 

Oh great! So my TB plate position is not the issue and I have to continue to investigate. Thank you so much for your imput and the infos shared.