revs drop too slowly

[colinstubbs 0]

When I take my foot off the accelerator the revs seem to hang on and drop quite slowly. I've changed the throttle cable and the actual throttle body returns quickly enough but the revs don't!! :x

 

Could it be an injector problem? I'm assuming that it has to be something after the TB, although I do also have a 'not completely closing' issue with that, but the idle revs only stick at around 1200-1500 max.

 

My problem is that it sounds like I can't bloody drive and leave my foot on the peddle at gear-changes, which I don't! Dammit! :censored:

[CorradoVR6-Turbo 0]

More info mate,engine type and year.... :wink:

[colinstubbs 0]

1990 1.8 16v with a webber redline single butterfly throttle body, panel filter and stainless exhaust, no other mods.

[dr_mat 0]

It won't take much leakage through the throttle body to make the revs drop slowly. I think you've answered your own question there ..

[colinstubbs 0]

In that case I just need flusted to tell me about the hole he had drilled in his butterfly 'to aid throttle on/off transitions' and hopefully that'll fix my idle being high sometimes as well. That will be a result, two birds with one stone and all that, with a bit of luck :roll:

[bcstudent 0]

I find my 1.8 16v holds on to revs between gear changes too. I figured it was just a side effect of a prehistoric fuel injection system!

[quicky1980 0]

possible isv fault??

[bcstudent 0]

Doubtful. It did occur to me that I've never actually checked the ignition timing though. When I changed the distributor I just set it by ear as I didn't have a timing light at hand and I've never checked it since. Job for sometime during the week there!

[jimmy83 0]

my 2.0 16v does this too......really annoying! although its going in for a sesh on the rr at stealth tmrw, so this might iron out/identify any probs.

[Henny 0]

give the ISV a clean... that's normally the cause of this on most valvers I've come across... (ISV = Idle stabilisation valve, nothing to do with the timing... ;) )

[Jim 2]

I find my 1.8 16v holds on to revs between gear changes too. I figured it was just a side effect of a prehistoric fuel injection system!

 

Thats more likely to be a sticky throttle cable if anything.. I used to get that on my G60 and a new throttle cable sorted it! :)

[colinstubbs 0]

I'll give the ISV a clean then, easy enough! It's just had a new cable which stopped it sticking at any random point between 2-4k! I shall prevail!!

[corradophil 3]

I agree with Henny and suspect the ISV is a bit sticky. When you come off the throttle the ISV is supposed to regulate the idle speed, but over time they get gunked up, which can cause the revs to drop slowly. I have experienced this exact problem on 2 of my cars, and solved it by giving the ISV a good clean up.

[bcstudent 0]

give the ISV a clean... that's normally the cause of this on most valvers I've come across... (ISV = Idle stabilisation valve, nothing to do with the timing... ;) )

Cheers for that, especially the patronising wink! I'm well aware that the ISV is unrelated to the ignition timing. The comment about the timing was nothing more than a thought that sprang to mind whilst considering other possible causes. Maybe I wasn't clear enough. The ISV advice is still valid though so, for that, I thank you.

 

Jim, my throttle cable is only a few months old. I'm pretty sure that the car's running properly to be honest and the 'holding on to revs' thing is only in comparison to other more modern cars. I haven't ever driven another 1.8 16v to compare. I don't really find it to be a problem so there's a good chance that colinstubbs's problem is more pronounced.

[dr_mat 0]

The ISV closes completely when you're on the throttle. It only opens during idle (obviously) and during zero-throttle overrun. It *may* be sticking open permanently, but I would have thought you'd notice other symptoms too (kinda like having the choke on too long!). Surely if it's sticky it'd be staying shut and the engine would stall every time you drop the revs?

I have to say, I'm sceptical about the ISV. Every time we get another "car not running right" thread, there's lots of suggestions to clean the ISV out. Now this isn't a bad thing, of course, cos it's free and easy, but I've rarely heard of cases where it actually fixes anything..

[corradophil 3]

Every time we get another "car not running right" thread, there's lots of suggestions to clean the ISV out.

 

I know what you mean, I've thought similar things with every fault being put down to the Blue temporature sensor or Lambda probe.

 

In this case, I have experienced this problem on two different cars, My Corrado, and my old Mk2 Golf GTI 8v running Digifant, on both cars it was the ISV at fault.

 

On the Golf I managed to strip and rebuild the ISV (I know its supposed to be a sealed unit but with a lot of messing around you can dissmantle it), just cleaning it with carb cleaner didn't work, but I got it there in the end.

 

On the Corrado a good soak with carb cleaner did the trick.

 

My observations are:

 

1. The ISV sticks open, making revs drop slowly and causing a fast idle.

 

2. The ISV sticks shut causing the engine to be unable to idle or to have a very low idle speed.

 

3. The ISV does not stick in one position but reacts slowly causing the engine to hunt badly and revs to drop slowly.

 

I am not saying it must be the ISV and cannot be anything else, but I beleive there is a good chance it will be the ISV.

[jezzaG60 0]

I've seen a lot of valver throttle bods where the mechanism has become a bit sticky, if you disconnect the cable and open it right up and let it go they can be slow to return. Usuallly fixed by a good session with some WD40.

 

Not that its likely to be the problem with the Redline single butterfly!

[colinstubbs 0]

Good news, I went to check out the ISV, looked at it and thought ,"Isn't there a leckie connection?" removed unit to find the plug had come off!! Obviously a complete tw@t had touched it last! :oops: :D

 

~I cleaned it anyway, and surprisingly enough seems to have cured my idle and slowly dropping revs problem! It's so nice when it's that simple :lol:

[dr_mat 0]

Simple case of non-functionality. Nice.

[gfunk1963 0]

Mine started doing that last night after I played with the throttle cable adjustment, I am certain little adjustment of the throttle cable will sort it out on mine.