need help with strange throttle, sticking?

[zskinner]

hi guys, this is my first post so i hope i do this right.

im after some help on a problem on my vp 3.8 auto, a few weeks ago this problem randomly started- ok so when i start the car up its all good, idles fine (anywhere between 600-900 revs) but as soon as i put the foot on the throttle the car wont slow down again when i take my foot off. so its like the car still thinks i have the accelarator pedal down a bit. also i have found that if i quickly jab the accelarator pedal and bring my foot off straight away the revs go back down to normal. example- if im cruising at 80 kms/h and the revs are at about 1600 revs, if i let my foot off the pedal it will just stay at 1600 revs and cruise at 80 kms/h like if i had cruise control, but if i quickly jab the pedal the revs will drop back down to about 1300 revs and the car will slow down like normal. i originally thought it was the acceleator cable geting stuck or something, so as a test i started the car up and just let it idle as normal, then i removed the accelarator cable from the throttle body and manually opened up the throttle body but still the throttle body wouldnt return all the way and stayed open a bit, so i think ive ruled out the accelarator cable sticking. i then did a ecu error check and got error codes 22 and 34.

code 22 is- Throttle position sensor below .2 volt for 2 seconds while engine running, and
code 34 is- MAP sensor voltage too low (< 0.25 v) with ignition on or engine running >1200 rpm and throttle open >20%

so i replaced both my TPS sensor and the MAP sensor with some spares i had laying around but still the problem hasnt gone away. the next day i did another error check but it reported everything was all good (code 12).

i really want to try and fix this asap so if anyone has any ideas that would be much appreciated. cheers

[D3V14NT]

Sounds like the throttle body is sticking. I'll never forget the first time that happened to me was in my first car - a 91 VN V6 - and only had my P's about a week. Put the foot to the floor and the pedal stayed there! I shat many bricks haha.

Take the throttle body out and give it a good clean out with some carby cleaner, have a bit of a look to see if anything obvious is causing it to stick while your there but I found the clean out was enough to loosen it back up again. Might even make it a bit more responsive. Careful with the IAC valve though as I've heard it has some parts that aren't too fond of carby cleaner.

[greenfoam]

I can't imagine a stock throttle sticking like that, you sure it's a stock one?. It would need to be very full of carbon to stick, it would be obvious

[D3V14NT]

I know when I took it off it had lost a few mm in diameter to the amount of carbon built up inside of it. Made a considerable difference when it was clean.

[zskinner]

thanks guys for the advice, i just cleaned out my throttle body completely making sure the butterfly was able to close all the way, but the problem is still there. so im going to replace the accelarator cable. i went down to repco and got one for 40 bucks but now im stuck. i cant find where the accelrator cable connects to the accelarator pedal. ive done a few searches on this site but cant really find anything through the search function. so can anyone tell me where it connects with these following pictures? cheers

[stocky]

remove that black plastic panel and you should be able to work it out

[zskinner]

ah true i had a feeling lol. thanks heaps mate, ill go give it a shot

[zskinner]

thanks heaps stocky i found it. i just replaced the accelarator cable but the problem is still there. anyone have anymore ideas? my head keeps telling me the TPS sensor that sits below the throttle body maybe just isnt letting the buterfly close or something, but its weird cos when the car is turned off the butterfly closes fine, its only when the car is on that the butterfly wont close. i was just down at holden and they quoted me $99 for a new TPS sensor, which i really dont want to spend unless im sure it will fix my problem. has anyone got any thoughts why you think its probably not the TPS sensor?

[zskinner]

would anyone maybe think it could be like a vacuum leak or the IAC or something perhaps ?????

[Tim Smtih]

I had the same thing. Someone recommended i use carby cleaner so i gave that a go, but no luck. And just to save you some heartache you're better off using kero or metho and some elbow grease to clean the TB. As you are no doubt aware if that stuff works its way into any of the sensors you're up for new sensors. I took the easy way out and pulled a TB off a '93 VR commy at the local wreckers, that and i cleaned up the tube leading from the TB to the MAP sensor. Either end had deteriorated with age so i trimmed 5 - 7mm off each end and good as new. You said you chucked in a new TPS, are you sure that unit is in good working order? I would have sworn that would have sorted this issue out. I think you are clutching at straws replacing the throttle cable but it's your money.

[greenfoam]

Well I think about now would be a good time to throw that throttle body in the bin (give it to someone to bore out to 70mm), maybe the blade is bent. Since you can often find another one for 10 bucks may as well just swap it

[D3V14NT]

Well I think about now would be a good time to throw that throttle body in the bin (give it to someone to bore out to 70mm), maybe the blade is bent. Since you can often find another one for 10 bucks may as well just swap it

My thoughts exactly, if a clean doesn't fix it and there's nothing obviously wrong, get a replacement. A little bit of money spent on a replacement can save a lot of wasted time stuffing around trying to fix it.

[zskinner]

yeah ok i might do that then. i didnt really want to get rid of it as it is a 65mm v8 one that cost me 80 bucks, but in all honesty i didnt notice any power difference at all compared to the stocko TB, maybe a bit better throttle repsonsiveness but thats it. ill grab another from the wreckers in the next few days or so and hopefully that'll do it. thanks again for your help

[greenfoam]

Didn't keep the original by any chance?, the stock V6 one is more than enough airflow so that's no problem

[zskinner]

nah im kickin myself that i didnt, i had 2 spare ones that i sold on ebay about a month ago but im only gonna get a 60mm this time, not gonna get another 65 or 70. have had both and neither made a difference. have heard theyre only good when you have a fair bit of engine work done and a good tune

[D3V14NT]

Some people can feel an increase in the responsiveness of the throttle with a 65/70mm but the standard 60mm provides plenty of airflow for a stock/lightly modified v6. I think the popularity of the 65/70mm throttle bodies stems from the relatively low cost of them rather than from any real power gains.

[zskinner]

anyone have any other ideas to what this could be before i go buy another throttle body tomorrow?

[Tim Smtih]

A service manual would have a troubleshooting guide in it, you could just sneak into your local repco and have a quick read through. There aren't many copies at the council library i've checked.

[wortus]

Have you checked the idle air control valve? Does the throttle move freely when it is disconnected from the cable? It's either got carbon deposits in it or the spindle is bent. My VY was sticking and hard to get off idle and that was just carbon deposits fixed by a clean.
Faulty TPS will just cause a flat spot when you try to accelerate, akin that to an accelerator pump on an old carby car, disconnect it and you will see.
If the throttle is closing off fully and the idle is still high it's either the IAC which bleeds air past the throttle to control idle speed or you might have an air leak somewhere so check all your hoses.
Otherwise perhaps a wiring problem back to the ECU or the ECU?

[yon]

is it the return spring?

[zskinner]

thanks heaps everyone for all your responses. i swapped over the throttle body for another one from the wreckers and it did the job, car runs great now. so anyone having the same problem as me, go get a cheap throttle body from the wreckers and swap it over. thanks again guys

[wortus]

did the 2nd hand throttle body come with an IAC valve and throttle position sensor and if it did, did you use them as well?

[zskinner]

nah it didnt come with another iac or tps sensor, so i just used the iac and tps from my original throttle body