Symptopms is this isv, maf or summit else?

[jonnaz]

the car idels slightly high. when i touch the throttle ie. pull away revs the revs go up and down between about 1200 and 1500 rpm revs will not increase unless you take your foot off the throttle and the press again further to get it past 1500 rpm. also when driving along as i take my foot off the throttle and press it again the it will nbot respond for a few seconds the suddenly the revs pick up jerking the car. any one got any ideas what might be causing it? doing my head in car is pretty much undriveabal

Thanks

[jameswkr]

Is ths an S2 or something else ?

[A80Avant]

check to see if the throttle body plug is in place.

whereabouts are you in newcastle? i may be able to help you with a diagnostic kit

[jonnaz]

yes this is an s2 3b, the throttle body plug is in i have checked, i have a dignostics machine and it brings up the codes for isv and the throttle sensor on the TB, it states on the dignostics throttle position sensor short, i have had the plug off sprayed with wd40 dryed but no diffrence, the problems posted above were occoring before the code for the throttle sensor showed up, how ever the isv code has always been there since i have beeing trying to fix this problem for weeks now oh well the joys of an s2

[twoqu]

I understand that you have pressure tested the car and found a leak around the throttle spindle. If it leaks under pressure it probably sucks unmetered air in under vacuum! So unless you have sorted that out then you might be chasing false faults!
Check the For Sale posts, add has a TB/TPS for £30 I think. Subject to verying its condition, that might be a quick win.

[jonnaz]

i have fixed the leak from the spindal on the tb and pressure tested again, dont have any boost leaks now.... that i know of, the car hold boost no cuts. i think i might replace the isv. i did test that it was sliding across properly but can it still be faulty if it does slide properly?

[twoqu]

Right! Have you disturbed the TPS ?
A quick test for the idle function of the TPS would be to bridge terminals 1 & 6 of the wiring connector with it connected and engine running. Just pull back the rubber boot. This simulates the closed contact (idle) position. If the idle improves then either the TPS is not adjusted correcly or its kaput!

[jonnaz]

i didnt remove the tps or loosen the screws that hold it on the TB. i will give that test a go and see what happens thanks for the help. i will post if it works or not. cheers.

[twoqu]

Whoops!
Make that 4 & 6! I think 1 is at the top and 6 bottom.
If you have a multimeter it shoud be continuity at idle and switching to open circuit when throttle is moved.

[jonnaz]

i dont think it is the tps sensor just did the test and when bridging terminals 4 and 6 rpm dropped to normal, the car was still cold so was on cold start mode. when at normal idel with the terminal bridged, i pushed the throttle to pull away speed and the revs still go up and down oscalliting between 1000 and 1200 rpm, me thinks this is the isv. anyone else got a diffrent opinion?

[jameswkr]

I dont think so. Try disconnecting the ISV. You will find the car a bit jerky to drive, but usable. Idle revs will be higher than normal c1000rpm but stable. Have you tried
unplugging the MAF and cleaning the terminals ? Is the exhaust dark when the car is mis behaving ? How old is the Lambda probe ?

[twoqu]

Well if the car idles acceptably when bridging those terminals then it would seem that the ISV is functioning correctly as its job is to regulate idle speed. By bridging those terminal we are simulating a closed throttle. As soon as the throttle is opened those terminals would be open circuit and the idle circuit would be broken. The test was only to prove the idle circuit including control of the ISV functioned.
I would think this points to the TPS. It is evidently not going closed contact at idle and may have worn tracks which provide intermitant contact for the rest of the rev range.
So you can try loosing the screws and adjusting the TPS by holding the throttle shut and rotating the TPS anticlockwise to a stop to see whether that achieves anything. Alternatively if you have a multimeter you can try and measure the resistance between terminals 1 & 2 (1500-1800 ohms) and terminals 2 & 3 (750 - 1300 ohms) increasing to a maximum of 3600 ohms at full throttle.
A fautly TPS is not uncommon!

[jonnaz]

ok i will have a little play with the tps when i get a chance. i have unplugged the maf and cleand the terminals its not the connection might be the maf tho i have cleaned it. the lambda probe i dont know how old it is not been changed since the car was baught and had stood two years previous to that. the car was running fine until engine siezed due to a spun bearing and i rebuilt the engine now having a few teething problems
drove the car today the revs did not dropp below 1400 rpm when at idel. then when i got bak in to go home the revs were normal at idel but doing the oscillating when the throttle was slightly touched.
thanks twoqu for your help i will do a bit fiddeling i let you know the outcome.

[220bhp]

I agree with Twoq, I had this same problem and it was the tps.

[newsh]

I have this oscillating when the throttle is lightly touched but I think not always, I also have the thing when I go along with a very light throttle at around 3k and then try to to speed up the engine falters before responding. Not as bad a yours I think but similar, I need to check my TPS too